Timothy Manning Swager (PhD '88), Research Leader in Supramolecular and Materials Chemistry

The story of Tim Swager's graduate admission to Caltech offers a poignant lesson in the importance of giving people a second look, in recognizing that intelligence comes in many forms, and in demonstrating that standardized tests can offer only an incomplete assessment on a student's future success. Now one of the world's premier researchers in the fields of synthetic, supramolecular and materials chemistry, Caltech celebrates Swager's achievements as one of the recipients of the Distinguished Alumni Award for 2024.

Born in rural Montana, Swager never let his difficulties with reading deflate his love of learning. At Montana State University, Swager excelled in chemistry, and he soon exhausted even the graduate offerings in chemistry. But before his low verbal score on the GRE nearly killed his application to Caltech, Professor Ed Abbot tracked down all of his chemistry professors to write letters on his behalf. It worked. Tim was accepted to Caltech, and just as important, he was accepted into the laboratory of Professor Bob Grubbs.

Swager recalls his graduate years as some of the most joyous in his life. Grubbs was in the process of embracing polymer chemistry, and his research group was abuzz with dynamic ideas and novel techniques. Swager flourished under Grubbs's guidance, and he benefited especially by heeding Grubbs's advice not to continue in synthetic chemistry for his postdoc. Grubbs felt that Swager had mastered the most important elements of this field, and the postdoc - at least those for whom an impactful professorial career awaits - is a time to branch out to new disciplines. Accordingly, Swager worked on electrochemistry, which laid much of the groundwork for his career, first at the University of Pennsylvania, and then at MIT. Today, the Swager group is pursuing a diverse range of projects that run the gamut of fundamental research, to applied chemistry projects that have been adopted in several commercial ventures.

In the discussion below, Swager explains why Bob Grubbs was such an important influence on his life, and he relates one very special day in 2005 when the Nobel Prize committee announced the winners in chemistry. Swager was serving as Department Chair at MIT, and he could barely contain his excitement when he learned that Grubbs and his MIT colleague Richard Schrock became Nobelists. It was a great day for Caltech and MIT, and a great day for Swager specifically.

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Wednesday, June 19th, 2024. It's my great pleasure to be here with Professor Timothy Swager. Tim, it's great to be with you. Thank you so much for joining.

TIMOTHY SWAGER: Great to be here.

ZIERLER: Tim, to start, please tell me your title and institutional affiliation.

SWAGER: I am the John D. MacArthur Professor of Chemistry at the Massachusetts Institute of Technology, and I'm a member of the Department of Chemistry.

ZIERLER: Let's start first with the name, John D. MacArthur, of course. In endowing this chair, is that connected at all with the MacArthur Foundation or the MacArthur Fellowship?

SWAGER: The chair was established at MIT for a long time. I'm not really sure how exactly it was funded. I haven't looked into it in detail.

ZIERLER: Tim, we'll get right to the occasion that brings us together, of course, congratulations on being named one of the distinguished alumni for Caltech in 2024. First, tell me what was it like when you got the news, and what does it mean to you?

SWAGER: It's not one of these things you apply for, so in that way it came out of the blue to me. I've always felt honored to be part of the Caltech family. When I was a graduate student, I was just surrounded by people that I thought were smarter and more brilliant than myself. From that standpoint, it's humbling and it was very special. I immediately told my wife, and she was very pleased as well.

ZIERLER: I wonder if it was an opportunity also, if you could tell me, to reflect on the value of the Caltech education and what you've been able to do with it?

SWAGER: I probably didn't need the award to reflect on that. Not a day goes by that I don't think about my time at Caltech. It was a very formative time in my life, where I felt like I had made it to the big league, at the cutting edge of science, and it was extremely exciting. Maybe I reflected a little bit more after this award, but I do reflect every day. [laugh]

ZIERLER: Tim, let's now go to some overall questions about your research. First at the broadest possible level, when you talk to non-specialists about what you do, what do you say? What kind of chemist are you?

SWAGER: I usually say just a chemist that works at the interface of materials science and, sometimes I add to that, the applications of materials.

Old Materials and New Properties

ZIERLER: Let's now go into the research itself. What aspects of your lab are devoted to fundamental research, and where are your starting points, applications, thinking about applying these research topics to societal benefit?

SWAGER: I think the delineation between fundamental research and applied research is not always simple, because sometimes a very fundamental discovery will have applications. However, in terms of research that is pushing the envelope on creating new materials properties at a fundamental level, maybe half of the lab is pursuing that direction. We're often trying to make materials with new or enhanced properties. But it is always the case that in doing so we are trying to make material's that have applications. So most everything we do involves developing a new composition and there was some innovation along the way. If you asked most of my students that are working toward an application, they would say that their research was fundamental. There's a gray scale there, and sometimes it's in the eye of the beholder where the fundamental begins and ends. But I've always resisted characterizing research that way.

ZIERLER: Is there an overall research emphasis in your lab that ties together all the disparate parts, one prevailing theme?

SWAGER: The enduring projects in the group all revolve around sensing of something, and this includes radiation, physical phenomena, biological molecules, or chemicals. We design materials that provide signal gain in response to what we want to sense. In essence, we try to put the intelligence in the materials so you can use cheap electronics, to create the interface with the user.

ZIERLER: I'll ask some more specific questions. Supramolecular chemistry, what does that mean here?

SWAGER: Supramolecular chemistry is a term that was defined by Jean-Marie Lehn. Most generally it is the chemistry of the non-covalent bond. For example, a classical polymer that we link everything together through strong carbon-carbon bonds or carbon-oxygen bonds. These bonds don't break at room temperature. But you could also make supramolecular polymers assembled by more weakly interacting species, like hydrogen bonds that are complementary. If you put enough of them in a collective assembly, you can generate material properties that are very similar to those created with covalent bonds. However, the weaker bonds can equilibrate and when cleaved can self-heal. Beyond the broadest definition laid out by Lehn laid supramolecular chemistry has other connotations. It is often used to describe assemblies of molecules that were designed to self-organize. So if you mix a bunch of molecules together, and form an amorphous goop, you would not call that supramolecular chemistry. But if you add them together, and they spontaneously assemble in some structure that is held together by non-covalent interactions, you would say that's supramolecular chemistry.

Chemistry as Locksmithing

ZIERLER: Tim, the term "molecular recognition," what is being recognized, and what is doing the recognition?

SWAGER: Molecular recognition is best understood through a lock and key analogy. You think about a lock, it has a place where the key fits in it, and the interaction is complementary. In molecular terms the lock is the receptor, and the key would be the guest. The receptor is also often called a host. In the broadest definition of molecular recognition if it not necessary for the host to envelope the guest. Two molecules could interact in a side-by-side fashion. For example, DNA recognizes its complement in this way and is a classic case of molecular recognition. In DNA, you have two strands that bind to each other with complementary hydrogen bonds.

ZIERLER: You mentioned chemical sensing, specifically chemosensors. I wonder if you could describe some of the signals that they're able to find.

SWAGER: We've worked with a number of different types of sensors. You name it, we've worked with it. One class that we've spent a lot time on used fluorescence as the signal. Fluorescence is a nice signal to work with because it's easily detected with photodiodes or photomultiplier tubes. We developed ways to enhance fluorescence responses through transport phenomenon. The concept is similar to how you get signal gain out of the transistors in your computer, that make use of the movement of electrons. In our methods we use the movement of the excited states—called excitons—and their movement creates signal gain. Other methods we've focused on make use of chemiresistors, wherein the signal is a change the resistance of a material. Here again get your signal gain because in nanomaterials there can be a limited number of pathways for the electrical transport. If you can block pathways, you can get very high gain when you have a limited number of paths. The analogy I use is that if you have a traffic grid, and you block a couple of intersections, you easily create a traffic jam. You make everything come to a halt. So if you design a finite number choke points that respond to your analyte, you can curtail the electron transport through materials and produce a large signal.

ZIERLER: Tim, your work, your lab's work in electronic polymers, I wonder if you can explain, is the electricity intrinsic in the polymers? Are you adding it after the fact? What does that look like?

SWAGER: Electronic polymers include both materials that can become highly conductive, almost like metals, and others that are semiconductors wherein it an activated process for charge to move within them. Those that can become highly conductive are often referred to as conducting polymers. To activate the conductivity the polymer is oxidized or reduced, that is, you have to subtract or add electrons away from the polymer. The polymer itself can be a neutral species, with no charge on it. But when you add an electron, then you have a negative charge that can move along the polymer. Equivalently if you take an electron out, then you have what you formally think of as a positive charge that can move. We call the charge carriers electrons or holes. That process of adding or subtracting electrons is called doping. The important feature is that with doping the conductivity change can exceed 10 billion.

ZIERLER: I know there's so much excitement nowadays in the field of carbon nanotubes and graphene. I wonder if you could describe your work in that area.

SWAGER: We've worked in both, and we like the carbon nanotubes for sensors because they naturally create the choke points that I mentioned before. They long objects that are very shape-persistent. It is like random networks of uncooked spaghetti between two electrodes. You're going to have junctions and the straight sections, and you can design interactions at these locations to affect the transport. The key is that with the high aspect ratio it doesn't take a lot of pieces of spaghetti to interconnect two electrodes. It'd be very different if we placed little balls between the electrodes; it'd take many more pieces to create a continuous pathway. The high aspect ratio is ideal for the chemiresistor signal gain concept that we came up with years ago.

Graphene is not as good, because if I take my traffic jam analogy, it is not the streets of LA getting jammed up, but is more similar to cars driving on a salt flat, where there are no roads. If there's an obstacle, they just go around it. Graphene doesn't have some of the intrinsic advantages of carbon nanotubes for sensors, but it's a pretty interesting material. We've worked to understand the dynamic chemistry on the surface of graphene, and the interesting reactions that can occur on this unusual surface of carbon atoms. These efforts would squarely fall into your fundamental category, where we don't really have an near-term application, but we felt it was important to understand the system.

The Renaissance in Liquid Crystals

ZIERLER: Tim, you've spoken about the scientific renaissance that liquid crystals are undergoing currently. I wonder if you could provide something of a history of the field, and what's so formative nowadays.

SWAGER: Liquid crystals were fascinating to me and I jumped into this area as a complete outsider as an assistant professor. It's very rich in soft matter physics with intellectual models about how matter organizes, depending on their shape and their intermolecular interactions. Cool questions to ask with molecules in this organized liquid state are: Do they want to splay? Do they want to bend? What are the consequences of intermolecular potentials? The concepts are very different from my chemistry training was really intriguing to me. In 1990 when I started my liquid crystal research the big success had been around making high performanc laptop displays, wherein the materials realign with the application of electric fields. Chemists were making new shapes that it seemed that with some effort we could transform any molecule into a liquid crystal if you cleverly decorate it with fluidizing sidechains. Liquid crystals were being discovered that had no resemblance to the classic rod shape of those that are in your laptop computer display.

We started making unusual liquid crystals based on transition metal complexes. These coordination compounds offered many different shapes and sizes and often have dynamic structures. A liquid crystal is technically a liquid, so it's not static, and we used these dynamics to produce intermolecular correlations between multiple metals. We produced dynamic coordination liquid crystalline polymers, that today we would call supramolecular polymers. These materials produced macroscopic dipolar domains that we could switch with electric fields to produce an effect called ferroelectricity. We also used the dynamics of coordination compounds to demonstrate cooperative chirality—handedness—and showed by assembling molecules that have a propeller shape in a one-dimensional column that the propellers spontaneously assembled such that they all turns in the same direction. Most recently, we took this effect further and showed that we could bias the direction of the propellor helix by with the application of an electric field. Most chemists might not think you could bias the chirality of molecule with electric fields. We were interested in this effect because chirality will give rise to a rotation of plain polarized light by retarding the propagation one of the circular components of polarized light. This is another example of a very fundamental effect that might find application in liquid crystal displays or light valves. There are other useful concepts from liquid crystals that can be used to make optical materials. You might remember that in the early days of liquid crystal displays, if you looked at them from the side, the colors were highly distorted. An innovation from Fuji Corporation revealed that liquid crystals with a discotic nematic that could coat a surface uniformly without defects and solve this problem. Here the molecules have a disc shape and when deposited on a surface they organize just as you would expect for coins on a table. If you put coins on a table, you would be really surprised to find one coin sitting up on its edge. They're all going to be lying flat and molecules can be made to do the same. This is a type of material that we're working on to make optical systems capable of imaging magnetic fields.

ZIERLER: Tim, I know that the NMR community has been a real beneficiary of some of your research. I wonder if you can explain how you've made advances in NMR and if that transfers over to some of the clinical aspects of MRI.

SWAGER: One advantage of being at places like Caltech and MIT's is you have colleagues who are visionaries. I was introduced to by my colleague Professor Robert Griffin to an NMR enhancement effect called dynamic nuclear polarization. NMR uses the alignment of nuclei in applied magnetic fields, and how they interact with each other and radio waves. It is a fascinating field that chemists use most often for structure determination. In healthcare you can use the lifetime of polarized protons in water for imaging. You typically use a contrast reagent, which relaxes proximate nuclei so they have a shorter lifetime, and also water has different dynamis in different tissues that also allows for lifetime imaging. If the tissue is restricting the water's rotation, it has a shorter lifetime. In dynamic nuclear polarization, you use electrons to polarize the nuclei. The magnetic field-gyromagnetic ratio-of an electron is much higher than a proton. The protons of water only interact weakly with the applied magnetic field, and there are only per million differences in the populations of two spin states. However with electrons, you get more than a couple orders of magnitude greater energy between the two states.

You get bigger signals if you excite coupled electron-nuclei transitions and by the diffusion of this spin alignment to its surrounding, you get what is called hyperpolarization. There are a number of applications and for imaging you can create hyperpolarized molecules or particles, and then you can inject them into people. In a well-known case, you take a naturally occurring molecule that is in all of us called pyruvate, you hyperpolarize it and inject it into a patient. The advantage of that is you're now observing an emission from only the hyper-polarized molecules. You can achieve high sensitivity by not having background. It's equivalent to looking at the stars at night in the desert. You can see the stars clearly because there's no background. You don't' see stars in the daytime because the strong interference from the sun. A group at the UC San Francisco has shown how to use dynamic nuclear polarization in clinical trials making use also of enzymatic activity. Bob Griffin and I started a a company, DyNuPol, that sold the polarization reagents, and we did work with clinical groups. The big clinical breakthrough has always just been always a few years away. [laugh] It's one of these things. The company was stable but not growing, and . I called it our nonprofit. We decided to let other people sell these reagents, and shut DyNuPol down.

ZIERLER: Tim, you mentioned, of course, your collaboration with Robert Griffin. I wonder if you can comment more broadly on the state of interdisciplinarity from your perspective at MIT. Is it easy enough to collaborate with biologists, engineers, even physicists? What does that look like for your lab?

SWAGER: I don't know if you've ever been to MIT—it's a very unusual place in that all the buildings are interconnected. In the Boston winter, that comes in handy.

ZIERLER: [laugh]

SWAGER: It is special that most departments don't necessarily have their own buildings. You will often be in a building that might have two or three departments. In fact, for many faculty their next-door neighbor might be from another department. It creates a natural melting pot of people and ideas and is different than other universities, wherein departments are siloed into different building. However, the building where I'm sitting right now is all chemistry because it's full of fume hoods. It's more of a machine than a building. But the MIT culture has been very helpful in my career. There are few scientists these days that would say they're not interdisciplinary. I do think that the MIT physical structure has enhanced my understanding in impact across disciplines. I think Caltech probably benefits a lot from its small size and—

ZIERLER: No Boston weather in the winter. [laugh]

SWAGER: No Boston weather. But you've got congregation spots. People go to lunch at the Athenaeum, right?

ZIERLER: Yeah.

SWAGER: If you're going to go to lunch at MIT, there are about 20 places within a few blocks. Caltech probably benefits from a different kind of mechanism, because of its small size wherein everyone eats together and knows each other.

Boston and Startup Science Culture

ZIERLER: Tim, you mentioned some of the start-ups. Beyond MIT, just being in the Greater Boston area, all of the start-up companies, all of the biotech, is that an asset for you?

SWAGER: Oh yes, definitely an asset. Boston benefits from amazing human resources. This is not just from MIT; we have Harvard, Tufts, Boston College, Boston University, Brandeis, U. Mass, and the list goes on. All of these universities literally are within a four-mile radius of each other. That's a really incredible concentration of academic activity. There are even more universities not too far away. Also, Boston has a fair amount of wealth and tends to attract venture capitalists. Collectively money and people make it work very well for startups. Students just don't want to leave the area. A funny thing that multiple students have said to me when they're looking for a job. When I ask, "What do you want to do?" They say, "I'm very flexible, but I would like to stay within three or four miles of right here."

ZIERLER: [laugh]

SWAGER: [laugh] They're so flexible, they don't want to leave their apartment. [laugh] We benefit from that, that talented people come to the Boston area and they don't leave.

ZIERLER: Now, you mentioned handing off some of this technology to others. Have you tried your hand at serving as a CEO?

SWAGER: Technically, we're not allowed to be company officers. This is a conflict of commitment issue for MIT, and I suspect other universities have the same rules. But I think most founders do get into executive decision-making in the early stages of their start-ups. Sometimes you might not have the title, you are not paid as a CEO, but you can have influence similar to a CEO. I've never put on the formal CEO hat, but I know what the job's like, and I do contribute in to CEO type activities. I do find myself sometimes being out of alignment, because the academic mindset is my core. I'm a teacher and want to share an understanding of the underlying technology and science. Investors are not typically interested in anything other than how will this company make money. It's just a different set of skills.

ZIERLER: Now, for the graduate students and postdocs in your lab, what's the rough ratio of who goes on to academic positions, who goes on to industry, who's interested in policy?

SWAGER: In terms of postdocs, most of them that work with me are considering a career in academics. They are strong scientists, and if they sure that they wanted an industrial job, they would have taken a job and not done a postdoc. Some decide it's not for them at the end and on average, probably 70% plus of my postdocs go into academia. There are fewer graduate students, probably about 30%, that go on to academia. They follow a number of different career paths. Some have gone on to do science and technology policy, which usually requires an fellowship in the Washington, D.C. area. A surprising number of my students over the last decade have gone into management consulting. I have never quite understood the job, but it appears that the goal is puzzling out how to save money or make more in a complex business. A very large number of my students want to go into start-ups. They like the start-up culture, which is really a lot like graduate school. They might take a slightly lower salary, but they get to work on something they think is exciting, and be part of a focused team. Beyond startups a number of them go into patent law.

ZIERLER: Interesting. I wonder if you could take me on a verbal tour of your lab, the most important instruments for your research.

SWAGER: Right now, my baby is a home built a spectrometer to do magnetic birefringence measurements. I mentioned earlier that we are developing materials to make optical magnetometers. In order characterize the materials we had to use electromagnet with a hole drilled through its poles so that a polarized light can be transmitted though materials in the sweet spot of the magnetic field. We measure that change in polarization over a broad wavelength to seek an understanding of how to create the optimal materials. So this spectrometer is the most special piece, because it's home-built. Everything else, we've bought. We have fluorometers, which are run-of-the-mill, but are workhorses that are constantly. We design materials that have intrinsic porosity from polymers that can't pack densely. They are like foam, but with molecular level voids and characterize these materials with a machine that measures gas adsorption isotherms. There are a number of other things, that are common to most chemistry labs and I just mentioned a couple that might be different from most.

ZIERLER: Tim, what about computation and modeling? Is this important for your lab?

SWAGER: Yes, it is and I got my first taste at Caltech. I took Bill Goddard's two course series called the Nature of the Chemical Bond. They exciting courses, and Bill was a very interesting teacher. He refused to let us take notes, and he would ask us questions throughout every lecture. He demanded your undivided attention and insisted that the TAs would take the notes. We were to be focused and taking everything in. If you didn't know the answer to the question you were supposed to say "duh". Silly but very effective. Bill wanted everyone do a computational project with him. So I did some computation through that course and afterwards computing some organometallic structures that were relevant to Grubbs group chemistry. Toroughout this experience, I realized how easy it was for the computer to give you the wrong answer, and how you had to a deep understanding to keep the computation from going off the rails. For the longest time, I resisted letting my students do computation out of caution from these earlier experiences. When they approached me about wanting to do quantum chemical calculations I would say, "Tell me a little bit about the different aspects of the Hamiltonian operator, and what it means electronically, and how do you think about bondin?" They'd all look at me like, "What? I just want to use the program."

ZIERLER: [laugh]

SWAGER: I told them that they needed to know more to be effective. The analogy I used was based on growing up in rural Montana. Sounds crazy, but it was the case that if you hadn't shot your first deer by the time you were 12, there was something wrong with you. If you were under 18, to get a hunting license you had pass a hunter safety course. This taught you about the safe handling a firearm. So I'd tell them about hunter safety, and then say, "Letting you go out and use this quantum chemical program without an basic understanding of what it does like giving a 12 year old a hunting permit without passing hunter's safety. Go learn more about this method, and then come back and we can talk about it." They usually never did follow up. However, today's quantum chemical programs have gotten so good now that I do trust students to do computation. In cases that are more complex, I connect them to other experts. Many of them are now experts. Currently, I have a student that pushed me to go beyond just electronic structure, to start thinking about how polymers with intrinsic porosity pack. It has been very exciting and now this student is probably spending two-thirds of her time on computation and she is co-advised materials science professor who's a computational expert.

Montana Roots

ZIERLER: Tim, let's go back now, to establish some personal history. Rural Montana, you have the state right behind you. I wonder if you could point to where you're from.

SWAGER: [laugh] I'm from Sheridan, Montana, which is a little place right there.

ZIERLER: Right in the mountains.

SWAGER: This is Bozeman, where I went to college. These are the Tobacco Root Mountains. This is what we call the Upper Ruby. This is the Ruby River. All of this is not so far from Yellowstone and the grizzly bears tend to wander over here a little bit more than we would like these days. My hometown was nestled right up against the Tobacco Roots at the mouth of three large creeks. There's a little delta there with 360 degrees views of mountains around you.

ZIERLER: Does your family go back many generations in Montana?

SWAGER: No. My parents were transplants. My dad grew up in Pennsylvania and was an East Coaster. My mom's from Kansas City. My dad got a deferment from the war in Korea, so he was in the prison service. After he did his deferment in the prison service, they wanted to move to the Northwest. My dad was a medical doctor, a general practitioner and wanted to practice in a small town. When he arrived my home town of Sheridan, there no hospital. He had his doctor's bag, an office and made lots of house calls. I was born in a house however currently when people have babies, they go to a bigger city, where they have all the equipment in case they have to do a cesarean or whatever is needed. In Sheridan they called my dad, Doc, just like in the old westerns.

ZIERLER: Now, growing up, were you always scientifically oriented? Did you have chemistry sets? Would you tinker?

SWAGER: Actually, no. This is where my background maybe differs from the average person. I always had trouble reading and, in fact, up until the fourth grade, they used to put me in special ed because I couldn't do the expected reading. They'd send me away from the class when they were doing group readings because I couldn't participate. It's a bit of a self-diagnosis, but I've always had trouble with spelling and reading. I get things backwards a lot. When I get nervous, I can't read anything, even if I have written it. When I get up and want to give a lecture, I'm very comfortable explaining concepts. But even when I put up a slide full of words and try and read it in front of a bunch of people, I simply can't make out any of the words in front of an audience. [laugh] It is likely dyslexia. So I was not a very good student, in my younger years. I don't think anybody would've expected me to be an MIT Professor. I worked on a ranch. In fact, I worked on my wife's grandfather's ranch under her uncle and first cousin I wanted to be a rancher and thought that I would start by raising pigs. My dad, being an educated MD, was not happy about this, and he was pushing me. So I went to college and started as an ag major. I started at University of Idaho. I don't have any transcripts from that year [laugh]. It wasn't a good year and wasn't a high point in my life.

After that academic year I worked on the ranch again and decided that I should give college another whirl. I decided not to go forward with ag and wanted to choose something that's interesting. I thought what about chemistry and making molecules? I'd had high school chemistry and knew about the concept of a mole and balancing equations. I just thought it's kind of like skiing, because when you grow up in Montana, you must learn to ski. Initially, if you can't ski very well, it's not really that much fun. You fall down all the time. But once you get really good at it, it's a lot of fun, and you can challenging run and not wreck, and you're not afraid. I thought, I bet you if I get good at chemistry, it'll be a lot of fun.

ZIERLER: Oh wow.

SWAGER: That was literally my thought process, and so I just decided I'll go do chemistry. I went to Montana State, and the faculty were spectacularly nice to me. I started doing research in the lab, and they let me have keys to the building. I really felt a part of that department, and didn't look back.

Caltech and a Second Look

ZIERLER: Who were some of the professors from your undergraduate years or the labs that were really formative in your development?

SWAGER: I worked for a few different people. From John Cardellina, I learned a lot about chemical characterization. I worked for him probably the most. But I worked with another professor named Pat Callis, who's still on the faculty. He's a physical chemist, and he convinced me that I should be a physical chemist. When I went to Caltech, I decided I was going to be a physical chemist. However, I didn't come out as a physical chemist. Bob Grubbs saved me from that fate, and I'm eternally grateful, because I think I would've been an average physical chemist. It just wasn't in my DNA. Back to faculty at MSU, one person that stands was the department head at the time. His name was Ed Abbott, and he played a major role when I applied to grad school. Because I have messed up a year—I decided to do my degree at MSU in three years. I took all the grad courses they offered in Physical Chem, inorganic, and organic. Everybody told me, "Oh, you'll get into any graduate school you want," because I was getting a high grade in every class.

So I only applied to Stanford, Berkeley, and Caltech. Back in the day, you would send out applications and wait for a letter to come back. I got rejection letters from both Berkeley and Stanford, and I was distraught. So I went to the department head, Ed Abbott, because I knew he had placed a classmate in with a distinguished professor who was not at as high of level of university. I asked him if he can get me into that lab. He was incensed that that Montana State's prizes student was reject. He called Stanford and Berkeley Chemistry, and they indicated the problem was the verbal test of the GRE. I recall there were paragraphs you have to read, and then answer questions. I couldn't read the paragraphs in the allotted time and had single-digit percentiles on the verbal portion of the test. Ed Abbott asked me, " have you heard from Caltech?" I said, "No." He said, "I sent somebody there. They know me. I'm going to call them." He called and it turned out I was slated for rejection. [laugh] But he talked to the graduate coordinator Pat Bullard, who was the den mother of all the graduate students, who confirmed this this story to me also afterwards. He told Pat, "Don't do anything. Don't send this rejection letter until you hear from me again." So she held onto the letter to reject me. Ed Abbott then contacted all of the Chemistry Professors at Montana State from which I'd taken a course for—I think about 15 professors—and had every one of them write a letter on my behalf, and he had it delivered by courier to Caltech.

ZIERLER: Wow.

SWAGER: I get a little choked up about this because it was—

ZIERLER: That's amazing. A beautiful story.

SWAGER: It was, it was. [Emotional pause] Anyway, sorry.

ZIERLER: That's OK. Tim what's the takeaway, that you can exhibit such strength in chemistry, and experience such difficulty on the verbals of the standardized tests?

SWAGER: It was only the verbal portion of the GRE. I've always been good at composing and writing. [laugh] Spellchecker has been wonderful, and I've compensated for my reading problems over the years. My colleagues know my reading comprehension is atrocious, but it's much better than it was. There are just different types of intelligence. When I look at the United States, in particular, I think somebody like me can make it here. In a lot of other countries, they tend to weed people like me out as a "person that is not academically bound." I was able to prove myself, and fortunately I got two shots on goal. I messed up the first time, I got a chance to start over again at Montana State. But I have tenacity, that comes from struggles in life. I often say "what doesn't kill you makes you stronger". My wife would say I'm very resilient [laugh], and I think that's really been the most important in my career. I always tell students, "think of your career like it is boxing, and you're going to get knocked down a few times before you figure out how to avoid those jabs. Every time you get knocked down, you've got to pick yourself back up off the canvas, and get back in there. " That's been my mantra.

ZIERLER: Tim, what year did you arrive at Caltech?

SWAGER: In 1983, the summer.

ZIERLER: When you started taking classes, how well prepared did you feel relative to your fellow classmates?

SWAGER: To tell you the truth, I was very nervous about this because I felt like I was from Hicksville. But the fact that I had taken many graduate courses. However, I had taken two and a half years of calculus and linear algebra at Montana State. I was going to be a physical chemist and was tole, "We think you need some more math." So I was placed in a graduate Mechanical Engineering mathematics course, which definitely showed me that my mathematical skills were subpar. [laugh] That was a course where I struggled, and was on a downward trajectory. When I finally decided I wasn't going to be a physical chemist and join the Grubbs group, the first thing I did was drop that course [laugh]. But I felt prepared overall. I teach organic chemistry at MIT, but I didn't take any organic chemistry at Caltech. It all comes from my undergraduate. Caltech was particularly good at is it's a good place for people that really want to grow and find themselves because they had no required courses. In fact, they encouraged you, to take courses outside of the area. A lot of the inorganic and a few of the organic chemists took Bill Goddard's physical chemistry course. I don't similar trends other places, and I think that special. People really were encouraged to not just be monolithic in their coursework, and so that was great.

Meeting Bob the Chemist

ZIERLER: What was the class or the interaction that made you a student of Bob Grubbs?

SWAGER: I had not initially talked to Bob when I started at Caltech. I knew who he was, but I was trying to decide between different physical chemistry projects. I remember this very well because I was walking not too far from the chemistry building and Bob Grubbs came jogging up to me. He had visited Montana State when I was an undergraduate, but I doubt he remembered me. Bob said, "I have a project, and Wyn Jennings (one of my professors from Montana State) told me you'd be perfect for it. Can you come talk to me?" It turned out that Bob wanted to get into electronic polymers, because his metathesis reaction was an ideal way to make these materials.

ZIERLER: Tim, if I could interrupt, if you can explain why, what was so ideal there?

SWAGER: Bob's reaction, olefin metathesis reconfigures double bonds, which can be used to allow electrons to delocalize.

ZIERLER: When you say Bob's, is this the Grubbs catalyst?

SWAGER: Olefin metathesis is not his invention, but is a reaction that Bob studied. I graduated seven years before the Grubbs catalyst was invented. [laugh] We were other people's catalysts before the invention of the famous Grubbs catalyst, which would've made my life infinitely easier—

ZIERLER: [laugh]

SWAGER: These other catalysts were so much harder to work with because of their high reactivity to water, air and other compounds. They weren't anything like Bob eventually came up with, and this discovery didn't come out of nowhere. Bob had already had the vision of this catalyst well before I joined his group. But back to why olefin metathesis and conducting polymers, Bob wanted to use the ability to transmutate carbon-carbon double bonds to allow electrons to be delocalized and materials to be electrically conductive. This was not long after the discovery of high electrical conductivity in organic polymers. Most of the publications were in the physics literature. People were trying to figure how these materials conducted and there was a great deal of spectroscopy and other measurement. It turned out Bob couldn't get his group interested in this project, and so he thought, "I'll go recruit a physical chemist." [laugh] I met with him, and he told me, "I don't know everything about these materials. I'd like you to teach me so we learn this together." Bob had some really cool ideas and it was just like a lightning bolt going through my head that told me "I like this is the guy and I'm going to work for him." [laugh]

ZIERLER: Now, from Bob's perspective, what's the skillset? What's the perspective that he was looking for in a physical chemist?

SWAGER: I might have even been giving him more credit on going after me as the physical chemist. One of the things he liked about me is he was told that I was a farm boy. [laugh] Helen, his wife, has told me that she thought that Bob saw a lot of himself in me. I don't know if you did his biography. But he comes from an extremely rural and not so dissimilar background from myself, where you had to be very self-reliant. He told me multiple times, "Farm kids are the best." [laugh]

ZIERLER: [laugh]

SWAGER: So maybe there was a little bit of looking for a physical chemist, but I think he might've been looking more for a farm kid. It was very nice to have somebody recruit you who was just so likable as Bob. I remember when I came into the group, a number of students basically asked me, "Who are you?" [laugh] I heard multiple times "This polymer thing probably won't work and you should think about another project because we are an organometallic group. We do catalysis, not polymers." However Bob was interested in polymers that he would come in the lab, and walk by everybody else to talk wo me a first-year graduate student—about my research. After we talked he would leave the lab, and the other students would be thinking is "Wait a minute. He didn't come see me." Pretty soon, other people started asking Bob for polymer projects. [laugh] His enthusiasm for the project made me fee like the special kid in this group. He was just so excited about getting into polymers.

Gateway to Polymer Chemistry

ZIERLER: Now, from your perspective, just the intellectual trajectory, how did Bob get to polymers, and why was it so exciting to him?

SWAGER: Before he came to Caltech, he had been at Michigan State, and he'd done some work on supported catalysis. In particular he worked with polystyrene beads, and grafted phosphine ligands from the surfaces. He mentioned this to me as sparking his interest in polymer science, in polymer chemistry. However, most importantly Bob had a knack for seeing the future. He had intuition that polymer chemistry which at some level had been perceived as a gutter science was ripe for innovation. At that time no top chemistry departments had a polymer chemist on their faculty.

He saw how sophisticated organometallic chemistry, was going to have a big impact and that many applications would emerge. Bob basically single-handedly transformed polymer chemistry in US academics. I've heard David Tirrell say this same thing, and Dave has been in the polymer science area for a long time and has a great perspective. Bob populated the faculties of many academic departments with scores of his great students doing amazing reseach in polymers. I was fortunate that I was the first person in the group focused on making new polymers.

ZIERLER: What eventually became your dissertation, how responsive was that to what Bob articulated in terms of his overall curiosity, his overall research objective in getting into polymer chemistry?

SWAGER: There were a couple of ideas that I can maybe claim credit. But the big ideas came out of Bob's brain. He sketched out things, as is appropriate with few details and it was up to me to work out the rest. That's the job of the grad student. A good grad student will figure out how to make his/her project or some variant of the project work. Bob had some really creative ideas that transformed the polymer community and stand equally to how his catalysis work impacted the organic chemistry community.

ZIERLER: Now, are there through lines, can you connect what you were doing, his interest in polymer chemistry, into what he would develop seven years later with the Grubbs catalysis?

SWAGER: If you look at the periodic table, on the left-hand side, the metals are referred to as early transition metals. They really like oxygen. If you make a bond between these metals and carbon, they tend to be moisture- and air-sensitive. They're very touchy compounds and all processes need to be carried out under nitrogen in rigorously dry and air-free conditions. This was the state of the art when I was a graduate student. However, if you can use metals from the right-hand side of the periodic table, the metals do not don't like oxygen as much. The metal-carbon bonds have more covalency, are less polar, and less prone to hydrolysis. The right side metals harder to oxidize and the organometallic compounds can be air stable. Bob knew if he could make an isolated catalyst it would be important. He knew it was possible because at the time there were different kinds of witches' brew recipes using late transition metals that people could put together and catalyze olefin metathesis. Back then people would mix a bunch of things in a flask and, all at once, whammo, you would get a metathesis reaction.

When I was in the group, there was a project that everybody wanted to stay away from. It was called the Late Metal Carbene project. Bob wanted people to make a metathesis-active catalyst, something the right of tungsten in the periodic table. Eventually, Bob struck gold with ruthenium, and he got some tidbits of information that this was the direction to from the results another graduate student Bruce Novak who was also in the group at that time. Then, some years later, another student SonBinh Nguyen synthesized what might now be considered the Generation-0 Grubbs catalyst.. I tell the story of Grubbs going pursuing this elusive catalyst for more than a decade, to my students. I also get obsessed with ideas and they wonder "Why do you keep harping on this?" I tell them, "Do you think Grubbs catalyst just happened one day? Bob had this vision and pursued that catalyst for more then 15 years [laugh] before he nailed it." It's hard to imagine a better catalyst and Bob might have found the absolute optimal family of catalysts. But it didn't come easy, and I take a lot of inspiration from that effort. If you really want to accomplish something important, sometimes you've really got to stick with it for a long time. As a faculty member, these challenge projects can be challenging, nobody wants to work on it because the last person failed. So I wait until there's nobody in the group that knows about the project, and reintroduce it as a brand new project. [laugh]

ZIERLER: Now, over the course of your graduate tenure, from the story you shared about being a first-year graduate student, and all the attention that Bob lavished on you, what were the demographics of the research group over the years you were at Caltech? Were there more and more graduate students doing polymer chemistry?

SWAGER: I remember Bob telling me that he got so excited about polymers that he was having to work hard to get students to work in his organometallic catalysis program. He said to me, "We went so far to polymers, nobody wants to do organometallic chemistry anymore. people only want to do polymers. I really want to get back to my roots." This was important because Bob was one of the best organometallic chemists of all time. In the last 20 years of his program, he did a lot of innovative organometallic chemistry that had nothing to do with metathesis. We single out Bob's greatness in the context of olefin metathesis, the Grubbs catalyst, and polymers, but there was much more to his career.

Making Polymers Conduct

ZIERLER: Tim, what was the basic research problem that fueled your dissertation? What were you looking for?

SWAGER: I was in love with trying to make the most conductive polymer ever. I worked a lot on polyacetylene-like material, which were the most conductive at the time. These were all carbon systems that were very delocalized. In hindsight, they were too air-sensitive to be really practical. One of the things that excited me when Bob presented the conducing polymer project, been reading a book on superconductivity of one-dimensional systems. Back then people thought that one-dimensional conductors would have a higher tendency to be superconductors because they can have a high density of states at the Fermi surface. I was in love with the idea that I could invent new superconductors. Maybe someday we will have superconductors at ambient temperatures, however 1D systems are not still considered the top candidates. But this was an inspirational goal. If I had continued chasing superconductivity in organic polymers with tunnel vision, it probably wouldn't have ended well because they are not likely candidates. There are limitations to these 1D systems that I didn't understand at the time, and maybe other people didn't either. However, I did have some ideas on the chemical sensing at grad school, and I actually conceived of a design that has been core to my research program that came out of observations I made when doing in-situ conductivity measurements.

I mentioned how you that you can dope polymers by oxidization or reduction. I found that if I gave these polymers whiffs of solvent vapor when they were doped, their conductivity would change by orders of magnitude. A fairly benign, non-reactive solvent, like tetrahydrofuran, it would completely kill the conductivity. I thought, wow, these things are really sensitive. I wonder if they'd make good sensors. In rationalizing their sensitivity, it occurred to me that these low dimensional systems will have restricted conductive pathways and with choke points that can interrupt the conduction. All of this gave me an idea, that I call the molecular wire kind of approach to making chemical sensors. I was in love with the high conductivity but, I realized there's some real utility in this behavior. As an assistant professor, I did play around with a couple systems to pursue the high conductivity game. But I quickly came around, and decided the sensing ideas is where I should focus my efforts. That's very long-winded, I know.

ZIERLER: No. That was great. Was Bob, during those years, was he already thinking about companies, and what ultimately would become Materia? Was he talking about those things?

SWAGER: When I was in his group, he was interested in transitioning things to commercialization, but I think it was still early. The entrepreneurial model for starting companies didn't really exist back then. That was just a really foreign world to academics. This has really changed and has become more mainstream for academics. These days the Federal Government expects your funding to creates new jobs and economic growth. That was just not part of any most funding agencies policies even when I first started as an assistant professor. So it was after I left Bob's group all the entrepreneurism really started happening. It gaining steam in the of mid-90s. I'm not sure when Bob started Materia, but it was a long slog, much more than a decade, for him. I'm glad that Materia was sold before he passed, and I know validation of the technology was important to him.

ZIERLER: Tim, what was Bob's style as a graduate mentor? How often would you meet with him? How useful was he, or how comfortable did you feel in approaching him with problems when you felt like you were coming up on a wall?

SWAGER: Let me start by mentioning that Bob was really good parent. Fundamental to being a good parent is like unconditional love. I felt that, as a graduate student, no matter what stupid mistake I would make, he wouldn't get angry or make me feel bad. People were really comfortable with him, because that's the way he was. I remember vividly Bob's classic daily cruse through the lab. He'd say, "What's up? How's it going?" That was your cue to run to the chalkboard, grab a spectrum, or do something to show him a new result. You only had an instant, when he'd come through, so I'd be ready to rip something out on a chalkboard. Bob didn't really help me with writing papers or anything. For my first paper, he suggested I ask a postdoc for help. By all accounts Bob was more of a hands-on advisor later in his career. I was there when his kids were young, and Bob was a most devoted father. In this context he has been a role model for me and he was there for his kids at all their sporting events and other activities. He referred to me later in my career that was "method to his madness." Saying "I let you figure things out for yourself," or "you learned to do this best on your own." I'm sure there were other people that maybe he gave more guidance. But with me, he was pretty hands-off on the publications and day to day research planning. I did send one of my first students to him, and I told him about how Bob interacted. My student reported back to me, "I think things have changed a little bit. He's a little more intense and much more on top of things." I think in the younger years of his kids, where things were different. But it was great. I honestly never had a bad interaction with the Tall Guy, as we called him, not even a single moment.

ZIERLER: When did the lab work feel complete? When did you feel like you had enough to defend?

SWAGER: Oh, I would've stayed there forever. [laugh] I enjoyed graduate school. Bob just told me, "I think it's time for you to write it up." The funny thing was, that Bob told me, "It should only take you about two or three weeks to write your thesis. Why don't you start writing then?" That sounded fine to me and I said, "OK." However, I must admit, it's hard to write a complete thesis in a couple weeks. It was before standard word processors, and I didn't sleep much. I really enjoyed working in the lab. I didn't relish the idea of leaving, to tell you the truth. I thought, "Oh, I have to leave, my time's up. [laugh] I need to create a open slot to let somebody else have fun."

ZIERLER: When you had to put it all together, you were sitting there intensively writing, what did you see as the principal conclusions of the research, even the contributions?

SWAGER: If I distill my thesis down, the main idea was, how can you make a conducting polymer that is something that you can process or manipulate? Most of the conducting polymers at the time had extremely poor material properties. They resembled brick dust. Bob had these ideas about how you could synthesize a polymer with rubber-like properties, and then do some clever rearrangement create a conducting polymer. The simple idea was to wave your magic chemistry wand over a polymer fiber and turn it into an electrically conductive wire.

We demonstrated skeletal rearrangements by unzipping of stringed rings. We did other in-situ reactions including elimination reactions and tautomerizations on polymers. My thesis was Precursor Approaches to Conducting Polymers. The precursors referred to the elastomeric polymers that were transformed into conducting polymers. In this way you could make an article from them, and perhaps even stretch orient the polymers, and then you could do a reaction and whammo change it into a conducting polymer. This approach was pretty new and prior to our work, Bob had tole me about the most interesting example that was developed a friend of his, Jim Feast. That provided the conceptual blueprint for the concepts we developed together.

ZIERLER: Now, the idea that, in the early days, polymer chemistry was perceived as in the gutter, was Bob able to swing around other fellow faculty members? Were other people recognizing the significance of what he was doing?

SWAGER: The fact that polymer was a "gutter science" was a thing, but he never called it that. [laugh] That characterization resonates in my head because when I was a postdoc, I went to a Polymer Gordon Conference. Back then, the conferences were nearly exclusively faculty and established industrial scientists. There very few grad students or postdocs attending Gordon Conferences. You apply to attend, and I thanked the organizer, Joe Kennedy for admitting me. Joe was a famous polymer chemist, but had spent his career in polymer science, not a chemistry departments. He said to me "I'm so glad you're here. You come from good stock. Grubbs has taken our field, which everyone thought was a gutter science, and he's elevated us. I'm really happy to have a Grubbs guy here." This is early days of Bob and polymers. The fact that this highly distinguished organometallic chemist doing polymer chemistry at Caltech, was something that really empowered people in the field. They could not consider themselves part of the academic elite. Joe Kennedy was a very distinguished polymer chemist and I was struck with how candid he was in his compliments to Bob.

ZIERLER: What postdocs, ultimately, in light of where you went, what kinds of postdocs were you looking for, and what kind of advice did Bob provide?

SWAGER: That's an interesting question, because I went to Bob multiple times with ideas, and he kept saying no. [laugh] My first time, I said, "I want to go do complex molecule synthesis." He said, "You're one of my best synthetic chemists. You don't need to go do a synthetic postdoc." I came back with the idea of doing physical organic chemistry studying, reactive intermediates at low temperature. He didn't like that idea or my ideas to do spectroscopy. Then I came to him with the idea of a postdoc at MIT studying molecular electronics, and related electrical devices. Bob said, "Great." So on my fourth time to his office with a postdoc idea, he gave me the go ahead. He had a little to no explanations for why didn't think the first three were not optimal. But Bob Grubbs had the proper intuition to steer me on the best career path.

Pivot to Electrochemistry

ZIERLER: What did he see in you? What was his vision for your trajectory?

SWAGER: I think I'm a grad student that exceeded expectations. Bob expressed to me multiple times that he would have never expected that I would be his first graduate student to be elected to the National Academy of Sciences. It's a pretty big thing in one's career. I have debated many times with my wife what it meant when he repeatedly told me this. I don't think he thought I was not as smart and I think he saw me as an innovator. However, it was clear that he didn't expect me to be the first among his students. There are now multiple Grubbs PhD students and postdocs in the academy. However, I feel lucky to be his first graduate student to achieve this. Bob was pleased and my colleague Steve Buchwald, a Grubbs Postdoc, was elected the same year. Bob made the effort to travel to Washington DC for the induction celebration and we have a photo of the three of us.

ZIERLER: What did you focus on for your postdoc?

SWAGER: I went to learn electrochemistry and work on microelectrochemical transistors in the laboratory of Mark Wrighton, also a Caltech PhD. I did some things on the side, and found that new soluble electronic polymers that I synthesized luminesced brightly. I started wondering if I could study the rate of the energy movement along the polymer's backbone to the end group. I dusted off a fluorometer that hadn't been used in almost a decade [laugh] and started doing measurements. These studies and understanding ended up being a predecessor to some of our sensing concepts.

ZIERLER: When were you ready to go on the job market, and what kind of jobs were you looking at?

SWAGER: Right now, postdocs seem to take longer in their positions. But I arrived July 1st of 1988 for my postdoc and 14 months later I went on the job market. It was pretty fast, and I had to work hard to have the portfolio results to give a lecture on my MIT results. I gave a lecture only on my postdoc work because my postdoc advisor stipulated I was to only talk about work from his laboratory.

ZIERLER: Did you ever have any idea leaving MIT that you would return as a faculty member? Were there any discussions along those lines?

SWAGER: No, not in my wildest dreams. [laugh]

ZIERLER: [laugh]

SWAGER: I thought of MIT faculty as gods; Caltech faculty as gods. I didn't see myself as a peer. In my third year as an Assistant Professor at University of Pennsylvania, I was unhappy with the situation, and I told Bob I was going to start looking around. He said, "No, no, no, no. People are watching you. [laugh] Wait, wait, wait. Good things are going to happen, be patient." I would have probably taken a lateral move at that time and Bob's sage advice again helped me in my career. I always tell people, I feel like I stumble along intuitively in my career, but I seem to fall uphill most of the time.

ZIERLER: Tell me about putting your lab together as a new faculty member at Penn.

SWAGER: I loved lab work. I set up everything in the lab quickly, and I started doing chemistry with my own two hands. This helped to get my program going fast and for most of the first projects a few of the reactions myself, and then then hand it off to a grad student. I was quite actively in the lab and when my wife would go California to visit her parents, and I would work about 18 hours a day for that time.

ZIERLER: [laugh]

SWAGER: Being a strong technical presence in my lab really helped my start and I've always told young faculty that you show students first hand so the believe that you can do the experiments that you expect them to accomplish. Since leaving the lab, I have had a few students that don't think I have a clue about the technical challenges they face. I had some really great students at University of Pennsylvania. I had a small group that at its peak was seven coworkers. But in terms of the manuscripts and results per student, it's probably higher than I've ever had at MIT. Those students worked really hard and I probably was suffocating them with constant 24/7 oversight. I admit that it was an intense time to be my coworker.

ZIERLER: Was one of the issues at Penn was that there weren't many people to collaborate with?

SWAGER: I don't want to get into the details. Some of the dynamics and leadership in the department wasn't great. But it's in the rear-view mirror and it is a different department today.

ZIERLER: Of course.

SWAGER: Basically, I ceased to see a career there and decided I was going to leave. Actually this was empowering, because when it's clear to everybody you're going to leave and they know you're not playing games, then other departments get very interested because they realize you're not trying to get just a salary bump. So my integrity in this process resulted in a number of departments courting me just before I received tenure. MIT was late to get involved and it was actually another Grubbs connection, Steve Buchwald who I mentioned earlier, that made this happen.

MIT had given me a tiny look a year earlier, having me up for a seminar. However, late in my time at Penn I called Steve and I said, "I'm going to probably move to Columbia. But if MIT were to make an offer…" and it so happened. I was very lucky and MIT had me an offer in just a little over a month. This was in part because they were at a record low number of organic chemists. Steve been a postdoc with Bob and I have thanked him repeatedly for the last nearly 30 years. I've known Steve since '83 when he was a senior postdoc in Bob's group. Bob, Steve, and I have had a lot of great times together over the years.

ZIERLER: Now, did you come up for tenure at Penn? How did you time that?

SWAGER: All of this happened right when I was up for tenure. The stars were in alignment I started getting outside offers, all at full professor. I can't imagine pulling something like this off again. I was pinching myself to make sure it was a dream for months, after being an Assistant Professor at Penn in June and being a Full Professor at MIT in July. [laugh] In all honesty the associate professor rank is not needed in academics. In fact, Caltech is a leader in this thinking and did away with the associate professor rank, a fact we continue to bring up at MIT, but with no progress.

Setting up Shop at MIT

ZIERLER: Now, coming back to MIT, first of all, did you basically pick up and reconstitute your lab from Penn, or was it an opportunity to begin anew?

SWAGER: I left some equipment behind at Penn. Basically stuff that I had bought with other faculty, or didn't want any more. All my students, save one who was about to graduate, wanted to move with me and MIT was very exciting to them. It is typical to move with your entire group. In fact, Grubbs did this, and when I joined the group was only a few years after the last of the Michigan State students had graduated. There were group members that had overlapped with the Michigan State team. Usually you bring your group with you. If students are almost ready to graduate they take a degree from their first institution. If they are earlier in the cycle, they switch and get a degree at the new institution.

ZIERLER: How did you step into the role so quickly as full professor? Was that jarring?

SWAGER: My wife remembers this as being a particularly intense time. She said, "You came in just so freaked out, wanting to prove yourself, and you went absolutely nuts working so hard."

ZIERLER: [laugh]

SWAGER: So, yes I went for it needing to prove myself again. I didn't think, "Oh, I'm a full professor. It's time to lay back." but rather, I was afraid that I would measure up and they would find out I'm a fraud. This is classic imposter syndrome, and its not a bad thing. It drives us and is very much alive with me. One of these days, people are going to figure out that I somehow cheated the system, and I shouldn't be here.

ZIERLER: [laugh] You'll have to fool Caltech also. [laugh]

SWAGER: [laugh] I think the most driven people often have this in the back of their mind.

ZIERLER: Sure. It's a motivator.

SWAGER: Yes, it's a motivator. If you start thinking you're smarter than everybody else, that's a much bigger problem. [laugh]

ZIERLER: Now, from Bob's assurance, you know, sit tight, people are paying attention, to your immediate elevation to full professor at MIT, at least if you could narrate the perspective from others, with all of this positive reinforcement, what was the impact you were having? What was the significance of your work at this point?

SWAGER: I think that it was clear that I had identified ways to use electronic materials to make sensors by the integration of molecular recognition into materials to create pressure points that can switch their properties in dramatic ways. I had done as an assistant professor hadn't caught the attention of many people, but it was apparently obvious to the people that mattered. I mentioned this idea of how we could amplify fluorescence by excitonic transport. The paper we published on that is nearly at 700 citations. However, for the first few years, I was the main person that citing that paper. [laugh] The concept of the paper, which is now mainstream, was lost on most people.

One of the most apparent changes in my career with the move to MIT was the attendance of my lectures at meetings. As an assistant professor at Penn, I'd go to American Chemical Society meetings, and on occasion I would only have an audience of about four people. After my move to MIT and, all at once, the room would be full. [laugh] It isn't really fair and there are a lot of great academics around the world that are underappreciated just because they are not at a famous institution, and it's so hard for young people in particular, to be recognized. I was also fortunate because of the collective success of all the Grubbs protégés. Bob's group was teaming for decades with spectacular postdocs and graduate students. Being part of the Grubbs clan gave me a little cachet, and helped make good things happen for me.

Curiosity and Chemical Sensing

ZIERLER: Now, you were explaining to me right at the outset of our conversation the importance of blurring the lines between thinking about applications and fundamental science. With the chemical sensing work, I wonder if you could explain what were some of the curiosity-driven questions, and then where was it obvious that this would have a life beyond the lab for you?

SWAGER: The curiosity started with a desire that to prove that transport along a molecular wire could amplify a sensing response. I imagined this scheme wherein if I created a molecular wire and I put a receptors at every site along the wire that basically quench the wires ability to transport charge, then only one site needs to be activated to kill the conductivity. However, proving this conclusively is really hard because you would have to do measurements on single wires. I had indirect proof, but was getting criticism by even suggesting this outlandish concept.. So I decided that I needed to prove it on molecules in solution, with an optical experiment, where single molecules in a dilute solution can be proved collectively as an ensemble. The ensemble, wherein we are seeing the collective behavior of many individual molecules gives a strong signal. We showed that semiconductive polymer wires amplify by transporting excitons rather than charge, but it is conceptually equivalent.

I had this insight but at the same time, looking back it's amazing how long it took me to recognize the differences between charge and exciton transport. Basically, I was trying to figure out how to make the solutions of our semiconducting polymer wires give more amplification. We investigated different electronic structures, but they all worked about the same. However after a couple of months I finally realized my electrical scheme was different because if you apply a voltage to a wire, it is analogous to a one-way highway. Everything's going one direction. But if you excite it with light, there's no potential field driving the excitons in one direction. They are simply doing random walk. If you consider random walk statistics in one dimension, you realize that for an exciton to diffuse 134 linear steps – a number we deduced experimentally – requires 134 squared steps. Random walls in one dimension is like randomly putting your your car in forward and reverse to travel along a street. It is very inefficient. So with the electrical wire schemes, I was focused on restricting the pathways that charge carriers would use, however I then realized that for exciton transport we want to let it diffuse in all directions. So in just going from dilute solutions with amplification factors of around 134, if we go to a continuous film wherein most every hop of the exciton samples a new site, we get a gain of 134 • 134, or about 20,000. We spent a lot of time also over the years studying the mechanisms of how energy flows within and between polymers. Asking questions about what are the relative rates? What electronic or organizational features are controlling the rates? Some of the sensing schemes that we're working on right now to detect PFAS that are known as forever chemicals. The ultra-trace methods we developed 20 years ago are still some of the best to deliver high sensitivity.

ZIERLER: Now, with the chemical sensing, all the work in conducting polymers, when did you first get turned on to the idea that carbon nanotubes would be useful for this?

SWAGER: As soon as carbon nanotubes were established as a new conductive allotrope of carbon, I started putting them into my patent applications [laugh] and this was literally before anybody else had made a chemical sensor using these materials. Those patents are now all expired. However, my thought was, "These materials are going to be really important. I'm going to use them to make chemiresistors." My first foray into carbon nanotubes was a little too early. It was still in the 1990s, and the materials were highly variable. Their properties were all over the place, and they weren't clean with lots of residual metal and amorphous carbon contaminations. I had asked a star student start a carbon nanotube research effort before we set up to characterize them. He came to my office after a few months and said, "Look, these things are black. They're not soluble. I can't characterize them. I have no idea what I'm dealing with. If you make me continue to work on these, I'll quit." [laugh] So I waited about about five years. There were better commercial sources of carbon nanotubes, and in 2005 we published our first papers in this area. We've had a good run with carbon nanotubes. We've been working with them now for more than 20 years now, have made a many sensors, and developed methods to functionalize them. We published reviews summarizing their utility in sensing. Overall we've expanded the field, and have shown how you can couple these materials to organometallic catalytic cycles to create sensors. In fact, one of our sensors leveraged one of Grubbs' modifications to the Wacker reaction. Bob had found that nitrite salts greatly enhanced the reaction and this addition helped us to produce superior sensors for the small molecule, ethylene, a universal plant hormone.

A Doubly Meaningful Nobel Prize Announcement

ZIERLER: You mentioned Grubbs, of course, 2005 when he won the Nobel Prize. I wonder if this was to some degree a group celebration of all the Grubbs alumni.

SWAGER: For me it was huge, I was the head of MIT Chemistry. Dick Schrock, who shared the prize with Bob, is my colleague. I was so convinced that they were going to win that year, that I told our president, Susan Hockfield "Be prepared. I think we're winning a Nobel Prize tomorrow." I had the room set up, [laugh] but didn't tell Dick. [laugh] The morning of the prize, I was dreaming that they had given it to biochemists I had never heard of, and I was upset. However when the radio alarm came on at 6 a.m. the radio came on, and immediately mentioned the prize. My wife remembers me jumping up and down on our bed, and she was afraid I was going to hurt her in my excitement.

ZIERLER: [laugh]

SWAGER: It was a spectacular day. I had a double whammy. Our department at MIT received a Nobel Prize as did Bob. I remember the day vividly.

ZIERLER: Why such a strong intuition that that was the year in 2005?

SWAGER: I was not alone, and the majority of synthetic chemists in the world had done at least one reaction using the Grubbs catalyst, so it seemed obvious. It was clearly a Nobel Prize worthy accomplishment. In fact it was overdue, in my view. If you asked synthetic chemists, "Who's most likely to win the Nobel Prize?" I bet that year 7 out of 10 chemists that year would've probably have listed Bob Grubbs.

ZIERLER: Now, beyond that very special day, did you enjoy your time as heading the chemistry department at MIT?

SWAGER: It's the type of position that has good days and bad days. It was an important professional growth experience. I think I grew up a lot during during that time and some of my rougher Montana hick edges got polished out [laugh], which was a good thing. I was comfortable on the big picture management and fund raising, but personnel issues can often be unpleasant. However, being a departmental cheerleader was fun. [laugh]

ZIERLER: From the perspective of the science, the academics, what were the most important things for you to focus on as chair?

SWAGER: I put a fair amount effort on fundraising, and started endowing summer fellowships for graduate students. These fellowships have grown and multiplied and now are a major resource in our department. My primary mission was to keep the department running really smoothly. Most often I was just taking care of things and shielding a my colleagues from unpleasant things. We have a Department Head structure, not a Chair. I did act as Head, and unilaterally made many executive decisions. If people didn't agree with what I was doing, they'd come, and argue their case. If I thought they had a good point, I'd make modifications, and they generally when back to their office happy. My goal, was to keep everybody properly resourced so that they can do their best work. I really thought about the job as a service role, but with authority to make swift executive decisions.

Focus on PFAS Regulators

ZIERLER: Tim, we'll bring the conversation right up to the present. What are you focused on? What are some of the big exciting areas of research in the lab?

SWAGER: I already mentioned our efforts on magneto-optical materials, and these days our porous polymer concepts underpin almost everything. We've been working on porous polymers for more than 25 years, and it's a very exciting field. Just last month, the EPA announced PFAS regulations. We had some very good sensors that make use of our porous polymers, and I was planning on eventually starting a company with that technology. But the EPA rules supercharged the field and required me to move the timing up. As of yesterday, we have a company called Fluorityxto commercialize our PFAS detection technology. We can detect these forever chemicals in under an hour, at levels below the EPA limits, which are in the low part per trillion range. This is all really exciting important. There big health risks as a result of PFAS in the environment and I feel good about the fact that we can help prevent exposure. At the same time, I've got a little bit of a pit in my stomach because I know there will be some hiccups. [laugh] Few start-ups make it without many make or break nail-biting moments. I'm strapping in for another roller coaster ride. What is different in my lift this time is that I have a 10-month-old grandson now, so at the same time it is a new phase in life. I am starting to think about an end game in my career.

ZIERLER: Sure. Tim, on that note, for the last part of our talk, I'd like to ask a few retrospective questions, and then we'll end looking to the future. Again, even though the boundary is still a little artificial, I wonder if you can reflect just on the different kinds of satisfactions in the world of discovery and the world of application. In discovery, what's been so meaningful to you about just what we understand about nature as a result of your work?

SWAGER: Wow. You know how to ask big questions.

ZIERLER: [laugh] That's why I save them for the end.

SWAGER: If I reflect, and I think about discovery, I think that it's important that we acknowledge that we usually don't understand science as much as we think we do. [laugh] Many times when I think I have a rock-solid understanding of an area, we stumble upon a result that doesn't fit. When you peel the onion back, there's always more to learn than you realized. These intricacies can hold the clues necessary to making things really work and make real progress. I take some inspiration from the semiconductor industry. Right now, semiconductor electronics, they make silicon with, 99.9999999% or nine 9s purity. This what it takes to make high performance devices. Then doing many semiconductor fabrication steps with greater than 99.9% yield is further impressive. Achieving the level of precision in semiconductor manufacturing took incredible attention to detail and many innovations. In chemistry we have to similarly focus on particular materials or reactions to create major future advances. This will generally require transference of concepts and methods from different fields. Chemistry and photoresistors are the foundation of modern electronics, although chemists don't generally get much credit. I emphasize to my students that Gordon Moore, a very important person for Caltech, began as a chemist.

ZIERLER: On the applied side, all the companies that you've been involved in, what are the most important satisfactions for the positive impacts they've had on society, how they've really helped people?

SWAGER: Our explosive detection system named Fido, has definitely indirectly saved many lives over the last 25 years. There's no question about it. As I mentioned, we are working to detect PFAS in our latest startup. We also have another company that's detecting pathogenic bacteria in food. There, again, people die from these types of exposures. I have been increasingly interested in environmental sensors. Trying to get new ideas into the mainstream, and broadly accepted requires a big push. I believe in the technology and am definitely a technology pusher. However, the market and investors in reality control the fate of any small company. I mentioned Materia, and Bob Grubbs had to be very patient. We call these types of companies hard tech. They take longer and fail more, but create jobs.

The Freedom in Scientific Truth

ZIERLER: Tim, you mentioned, you know, thinking about the DAA Award, not a day goes by that you don't think about Caltech. We've talked about Bob throughout our conversation. More generally, what has stayed with you from your Caltech days, just about what it means to be a scientist, what it means to do good science?

SWAGER: It is pretty fundamental to me. The Caltech motto is "the truth will make you free". This might be lost on some people, and sometimes in science people will distort or embellish their contributions. Caltech also had an honor system on exams and you didn't take an exam in a room. From day one at Caltech, I felt that the culture was to be a virtuous scientist. I tell my students, "You can't bury a piece of data because it doesn't fit." In fact usually that piece of data is telling you something profound [laugh], and if ignored you're going to get it all wrong. The truth will make you free. The Caltech philosophy trained me and prepared me to be the best scientist possible.

ZIERLER: Finally, Tim, last question. Looking to the future, being a grandfather now, thinking about this stage of your career, time is such a valuable resource. There's so much work to do. There's so many things to concentrate on. How are you going to prioritize for what's most important?

SWAGER: [laugh] The biggest problem for me is to quit starting new projects.

ZIERLER: [laugh]

SWAGER: [laugh] I will try to finish developing some of the concepts we have started. We've done quite a bit in the porous polymer area and I'd like to see if we can commercialize some of these materials. Another thing on my bucket list is to progress our magneto-optical materials to where they also can have real world utility. I need improvements by a factor of 30, to be golden there. To make an impact in healthcare, we invented lateral flow assay, that operate like your COVID tests, but are ultra-sensitive and intrinsically quantitative because they operate on resistivity changes rather than optical signals. I would love to produce low cost home diagnostic systems. Those three pretty big, tall orders to do in about a decade. I might only achieve one or two out of the three. But those are my aspirational goals for the end game. Bob Grubbs used to always joke that his goal was die funded. [laugh] He achieved that goal, but I'm hoping to retire before then. [laugh]

ZIERLER: Tim, this has been a wonderful conversation. I want to thank you so much for your time, and I look forward to meeting you when you come out to Caltech.

SWAGER: Me too. Thank you for the interview.