Seth Marder talks to Gavin Armstrong about organic electronics, two-photon chemistry and surface patterning.
Seth Marder is professor of chemistry at the Georgia Institute of Technology, US, and director of the Center for Organic Photonics and Electronics. His research focuses on how the chemical structure of molecules and materials relates to their electronic and optical properties. Seth is on the advisory editorial board for Chemical Communications and Journal of Materials Chemistry.
You have a fundamental interest in how materials interact with light and electric fields. What prompted this interest? While I was a postdoc at Oxford, I read an article on organic nonlinear optics. I realised I could make organometallic compounds that could expand upon what people were doing with organic compounds. I ended up trying to make a compound and isolating an unwanted side product. The side product had very interesting nonlinear optical properties that resulted in a paper in Nature. While I understood the basic design guidelines to make compounds that could work, I didn't really understand the underlying physics behind why they worked. Conversely, I realised that while physicists understood the physics of nonlinear optics, they didn't really understand how chemical structure intrinsically maps onto the nonlinear optical properties of materials. One thing led to another and 22 years later, I have a better understanding than I did when I submitted that first paper.
Some of your research involves two-photon chemistry. Can you explain what this is? Two-photon absorption is a nonlinear optical effect in which a molecule simultaneously absorbs two photons of light. It's significant because the probability of this happening scales quadratically with the intensity of the light. Consider a beam of light that is focused to a point on a material: if the material is a good two-photon absorber, you can have efficient absorption right at the focus. The rate of absorption of light will fall off quadratically with distance from the focus. This means you can localise where you excite the material. This has important ramifications if you want to do three dimensional fluorescence imaging or if you want to write three-dimensional structures.
My colleagues and I have spent many years trying to understand how to make two-photon absorption of light by molecules very efficient. We've also worked on coupling the efficient absorption of light with other properties, such as the ability to initiate chemical reactions. The structure-property relationships that our team have developed are now widely accepted as a standard paradigm.
You are also interested in organic electronics. What are you currently working on? We are trying to develop materials that are effective at transporting charges and absorbing light in the correct wavelength ranges for photovoltaics. We are looking for sets of materials that have the correct energy levels that allow them to be used most effectively together.
Bernard Kippelen and I have been working on a polymeric system in which the backbone is not electronically active itself, but has pendant groups that are. This allows the polymeric properties to be decoupled from the electronic properties. We hope to get some of the processing advantages of polymers whilst avoiding some of the issues that occur with conjugated polymers, where a defect in the polymer strand can affect the activity in the whole strand.
What other projects are you working on?
"If you cannot explain to people what you're doing and why, you've not done your job as a scientist"
Another area that I think is very important is interfacial chemistry. My collaborators and I have recently reported a new kind of nanolithography called thermochemical nanolithography. It is related to IBM work on the 'Millipede Project.' They took arrays of atomic force microscopy (AFM) tips that could be heated from room temperature to 1000 °C and back in the order of a microsecond. They used them to put divots in a polymer surface, individually controlling each tip. They later used the tips to read the surface, like reading Braille. We used a crosslinked, and therefore mechanically robust, polymer featuring esters with active leaving groups. We then took the atomic force microscopy AFM tip over the polymer and heated it, converting the esters to carboxylic acids and thus changing the chemical reactivity of the surface. This allows you to use that surface for a subsequent chemical reaction or a molecular recognition event. I think that this is an exciting area and it will be a very complementary technique to dip-pen lithography.
What is the secret to being a successful scientist? Much of our work is interdisciplinary and collaborative. For the collaborations to work, it is necessary to build strong human relationships along with the science. I have found that good relationships with good people, typically results in good science. If you have bad relationships even with a good scientist, I think one can find it very frustrating.
I always try to teach my students to look at their data as if they were somebody who had nothing to do with the work; the ability to look at things from a distance and suppress bias is absolutely essential. Also, the ability to realise when you've hit on something important that may not be what you were going after is important. You must have an awareness of what's going on elsewhere. I believe that having adequate breadth in what you are interested is also essential for creativity.
I also think an absolute desire to be a good teacher is essential. If you cannot explain to people what you're doing and why, I think you've not done your job as a scientist.
Which scientist do you admire? Jacob Bronowski was a mathematician, a biologist and a philosopher. He wrote a book called 'The Ascent of Man,' which the BBC made into a TV series in the early 1970s. In one of the chapters, called 'Knowledge or Certainty,' he talked about the danger of arrogance as a scientist, and thinking you have absolute knowledge when in reality you never can. The image of Bronowski standing in a pond at Auschwitz talking about how arrogance and dogma led to his family's ashes being in that pond was probably the single most influential event in my life as a scientist. It was a transformational point for me. It really emphasised the need for us to realise the humanity of what we do and our intrinsic fallibility.