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Exciton Migration and Dissociation in Conjugated Molecular Materials

Speaker: Peter Rossky, University of Texas at Austin
Series: CBE Departmental Seminars
Location: Elgin Room (E-Quad A224)
Date/Time: Wednesday, October 2, 2013, 4:00 p.m. - 5:00 p.m.

In order to develop a working chemical intuition about electronically active organic materials, and particularly with the goal of developing design principles for organic photovoltaic materials, it is imperative to understand the relationship between molecular-level structure and the electronic excited state phenomena of exciton migration and charge separation dynamics both within conjugated polymers and at organic donor/acceptor interfaces. In this presentation, recent progress in simulating these processes, using a mixed quantum/classical molecular dynamics approach that employs an all-atom description of the intermolecular interactions coupled with semi-empirical electronic structure will be described. The results of exploring several systems at ambient temperature will be discussed, including phenylene-vinylene and thiophene oligomers, as well as cyanine and fullerene components.  The roles of molecular structural fluctuations and intermolecular electronic couplings, as well as the roles of donor and acceptor excited state energy alignments will be discussed in the context of exciton transport and dissociation.  The development of a molecular-level interpretation of experimental ultrafast time-resolved spectroscopic probes of these processes in a layered phtalocyanine-C60 system will illustrate the mechanistic insight accessible via such simulations.

The results reported here are based on work supported as part of the Understanding Charge Separation and Transfer at Interfaces in Energy Materials (EFRC:CST), an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001091.