Customer Interview: Photophysics Researcher, Prof. Hanson – Florida State University

We were delighted to talk to Prof. Hanson from Florida State University to find out about his work in the field of photophysics research and how he has been using our FLS1000 Photoluminescence Spectrometer and LP980 Transient Absorption Spectrometer. His research is dedicated to understanding and controlling photoinduced electron, energy, and proton transfer events for applications including solar energy conversion, catalysis, and photochemical separations.

1. Since starting at FSU, your work has primarily focused on studying the photophysics of self-assembled molecules on metal oxide surfaces. Could you please summarise why you started there and what your group has been up to?

I was first introduced to dye-metal oxide interfaces during my postdoc at UNC Chapel Hill where our goal was to use these interfaces for photocatalytic water oxidation and proton reduction. That experience sparked my interest in the power of self-assembly to control structure at these interfaces. Since starting at FSU our research group has focused on using metal ion-linked multilayer assembly at these interfaces to control the rate, yield, and direction of energy and electron transfer. For example, we have demonstrated that the nature of the metal ion and the first molecular layer is an effective means of controlling the mechanism of electron transfer between a dye and the surface. Or by tuning the energetics of two layers of dyes we can increase broad-band absorption and improve solar energy conversion efficiencies. More recently we have demonstrated that molecular assembly at the interface is an effective means of facilitating singlet fission and low energy sensitization. Arguably our most successful implementation of this strategy is to harness molecular photon upconversion in a solar cell.

2. Triplet-Triplet annihilation for application in solar energy conversion has been a consistent theme in your work; how can this be used to increase solar cell efficiency and achieve a more carbon neutral future?

One of the primary loss mechanisms limiting solar cell efficiencies is the transmission, or lack of absorption, of sub-band gap photons. One intriguing strategy to circumvent this limitation is by using photon upconversion, combining two low energy photons to generate a higher energy excited state, to harness those sub-band gap photons. While the idea of using photon upconversion in a solar cell is not new, its implementation has been challenging. Most of the effort has focused on using upconversion filters as an external component to current solar cells. Our groups primary contribution to the field has been to integrate upconversion directly into a solar cell. We use multilayer assembly of acceptor and sensitizer molecules on metal oxide surface to obtain the highest photocurrent yet generated from photon upconversion under standard sunlight intensities. Coupling our upconversion multilayers to record breaking solar cells may offer a means of pushing solar cell efficiencies beyond their current limitations resulting in cheaper solar cells and new alternative energy opportunities.

3. Do you have any other research projects going on that you are excited about?

We have two other independent projects being pursued in our lab. The first is to harness the dramatically increased acidity of certain dyes to facilitate chemical transformations via excited state proton transfer (ESPT).  We demonstrated ESPT dyes can both catalytically and eneantioselectively protonate organic substrates. More recently we showed that after the addition of a chiral directing group, ESPT induced isomerization is an effective means of enantioenriching racemic mixtures of BINOL. The second project, in collaboration with the FSU, DOE-EFRC: Center for Actinide Science and Technology, is focused on using wavelength selective excitation to separate a mixture of metal ions. We look forward to expanding our efforts in both of these domains in the near future.

4. You use many types of spectroscopy and material analysis in your work; how have Edinburgh Instruments’ Spectrometers facilitated your research?

At the heart of all the research endeavors mentioned above, is understanding how the structure of molecules and/or interfaces dictates the rate and efficiency of photoinduced events. Given that many, if not most, of these projects contain multicomponents and have multistep processes, fully characterizing these materials is often a non-trivial task. That is why we regularly use a combination of steady-state and time-resolved emission and absorption measurements and comparisons between samples and controls to decipher the excited state dynamics and mechanism. Aside from our UV-Vis spectrometer, there is no question that the Edinburgh FLS980 and LP920 are our highest traffic instruments. Beyond the base builds, these instruments offer enough flexibility for us to feed additional lasers into the spectrometer, measure quantum yields with an integrating sphere, and perform magnetic field dependent spectroscopy, to name a few.

Prof. Hanson received B.S. in Chemistry from Saint Cloud State University in 2005. In 2010 he earned a Ph.D. under the mentorship of Mark E. Thompson at the University of Southern California where he designed new near-IR dyes for application in organic light emitting diodes and photodetectors. Then, as a postdoctoral scholar under Thomas J. Meyer at the University of North Carolina at Chapel Hill (2010-2013), he studied organic-inorganic interfaces for application in photocatalytic water oxidation/reduction. His independent research career began in 2013 at Florida State University (FSU) as a member of the Department of Chemistry & Biochemistry and the Materials Science & Engineering program. During his last 5 years at FSU he has published over 45 papers, received the National Science Foundation-CAREER award, Army Research Office-YIP award, and most recently the Inter-American Photochemical Society’s Young Investigator Award.

Notable References

• Hill, S.P.; Hanson, K. Harnessing Molecular Photon Upconversion in a Solar Cell at Sub-Solar Irradiance: Role of the Redox Mediator. J. Am. Chem. Soc. 2017, 139, 10988-10991.https://pubs.acs.org/doi/abs/10.1021/jacs.7b05462
• Wang, J.C.; Violette, K.; Ogunsolu, O.O.; Hanson, K. Metal Ion Mediated Electron Transfer at Dye-Semiconductor Interfaces. Phys. Chem. Chem. Phys. 2017, 19, 2679-2682.https://pubs.rsc.org/en/Content/ArticleLanding/2017/CP/C6CP07939C#!divAbstract
• Salpage, S.R.; Lanzetta, R.C.; Zhou, Y.; Wang, J.C.; Hanson, K. Wavelength Selective Separation of Metal Ions Using Electroactive Ligands. Chem. Commun. 2018, 54, 7507-7510.https://pubs.rsc.org/en/content/articlelanding/2018/cc/c8cc03371d#!divAbstract
• Ayad, S.; Posey, V.; Das, A.; Montgomery, J.M.; Hanson, K.Enantioenrichment of racemic BINOL by way of excited state proton transfer. Chem. Commun. 2019, Advance Article.https://pubs.rsc.org/en/content/articlelanding/2019/cc/c8cc07949h#!divAbstract
• Dilbeck, T.; Hanson, K. Molecular Photon Upconversion Solar Cells Using Multilayer Assemblies: Progress and Prospects. J. Phys. Chem. Lett. 2018, 9, 5810–5821.  https://pubs.acs.org/doi/10.1021/acs.jpclett.8b02635

For more on Prof. Hanson’s group and their work, join them on Twitter @HansonFSU.

Fluorescence Spectrometers for Photophysics Research

Edinburgh Instruments fluorescence spectrometers and LP980 transient absorption spectrometer were used to enable Prof. Hanson’s photophysics research. To find out how our fluorescence spectrometers can help you with your photophysics research, simply contact a member of our sales team.

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