Bardeen Research Group

Department of Chemistry | University of California @ Riverside | 501 Big Springs Road | 127-131 CS-1

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Bardeen Research Group
University of California, Riverside * Department of Chemistry
501 Big Springs Rd * Riverside, CA 92521, USA
Phone: +1.951.827.2723 * Fax: +1.951.827.4713 * Email: christob@ucr.edu

 

Organic Materials

Putting Photons to Work Using Organic Materials

Photons are ideal energy transporters. The best and most obvious example is the transport of energy from the sun to the Earth over a distance of 93 million miles without loss. Once the photons arrive, their energy has to be transformed efficiently into a more useful form, like an electrochemical potential or electron-hole pair (the photovoltaic effect) or mechanical work (photoactuation).  We are interested in using organic materials, especially ordered materials like molecular crystals, to find better and more efficient ways to achieve this transformation. Some areas of our research include:
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1.  Exciton Fission in Crystals and Covalent Assemblies.

 One way to increase the overall efficiency of solar cells is to have one high energy photon produce two or more electron-hole pairs.  The idea is that when one photon is absorbed, the newly created excited state will spontaneously split into two or more lower energy excitons, in a process called Multiple Exciton Generation. 

We are interested in producing organic systems, like tetracene, that exhibit Exciton Fission, where a high energy singlet state splits into a pair of lower energy triplets.  This can occur in both covalent dimers and in crystals.

 

2.  Photophysics and Electronic Energy Transfer in Crystals and Dendrimers. 

Currently, one limitation of the efficiency of polymer-based organic solar cells is their low exciton diffusion lengths, which are typically on the order of 10 nm or less.  One way to improve transport is to use highly ordered, crystalline materials that can support delocalized electronic states and coherent transport.  We are studying both the basic photophysics of organic molecular crystals to understand the origin and size of delocalized states.  We are also studying how disorder affects the energy transfer dynamics in more disordered systems like dendrimers and amorphous polymers. 

3.  Photoactuated Motion in Organic Nanostructures.

 When a molecule absorbs light, it can undergo a photochemical reaction that requires molecular motion on the Angstrom scale, for example a cis-trans isomerization or a 4+4 cycloaddition.  When many such reactions are lined up and occur together, the total displacement is the sum of all the smaller displacements and can be quite large.  We are using molecular crystal nanorods to harness this effect in order to develop nanoscale photomechanical actuators, which could permit the remote control of very small objects in environments like the interior of a live cell.

 

Publications (for a complete Publication list, see Publications link)

  1. "How morphology affects singlet fission in crystalline tetracene,"G. P. Piland and C. J. Bardeen, J. Phys. Chem. Lett., 6(10), 1841-1846 (2015).

  2. Sulfur-bridge terthiophene dimers: how sulfur oxidation state controls inter-chromophore electronic coupling," C. D. Cruz, P. R. Christensen, E. L. Chronister, D. Casanova, M. O. Wolf, andC. J. Bardeen, JACS, Ahead of Print (9-2015)

  3. "Excited-state dynamics of diindenoperylene in liquid solution and in solid films," V. M. Nichols, K. Broch, F. Schreiber, and C. J. Bardeen, J. Phys. Chem. C, 119(23), 12856-12864 (2015).

  4. "Hybrid molecule-nanocrystal photon upconversion across the visible and near-infrared,"Z. Huang, X. Li, M. Mahboub, K. M. Hanson, V. M. Nichols, H. Le, M. L. Tang, and C. J. Bardeen, Nano Lett., 15(8), 5552-5557 (2015).

  5. "Synthesis and photophysical properties of a "face-to-face" stacked tetracene dimer," H. Liu, V. M. Nichols, L. Sehn, S. Jahansouz, Y. Chen, K. M. Hanson, C. J. Bardeen, and Xi. Li, Phys. Chem. Chem. Phys., 17, 6523-6531 (2015).

  6. "Ligand binding to distinct sites on nanocrystals affecting energy and charge transfer," X. Li, L. W. Slyker, V. M. Nichols, G. S. H. Pau, C. J. Bardeen and M. L. Tang, J. Phys. Chem. Lett., 6(9), 1709-1713 (2015).

Reviews

  1. "Triplet excitons: bringing dark states to light," C. J. Bardeen, Nature Materials, 13, 1001-1003 (2014).

  2. "The structure and dynamics of molecular excitons," C. J. Bardeen, Annual Rev. Phys. Chem., 65, 127-148 (2014

 

fission gif
Exciton Fission occurs when the excited state splits into two or more lower energy excitons following the absorption of one photon by molecules like bis(tetracene).
anthracene
Experimental and calculated emission spectra from polycrystalline anthracene films.  The enhancement in the 00 peak at low temperatures is a symptom of greater exciton delocalization, leading to superradiance.
Reversible bending of a single 50 mm long 200 nm diameter nanorod using 2-photon excitation.  The circles mark locations on the rod that were exposed to the laser (b, d, f).
The nanorod relaxes for 2 minutes between irradiation periods.