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1. Novel Means of Determining Exciton Coherence from the Photoluminescence SpectrumFrank C. Spano, Temple University, DMR 0906464 Intermolecular interactions drive charge and energy transport in thin films of conjugated organic molecules. Such films comprise the active ingredients in organic-based solar cells. Key to understanding transportis exciton coherence.Based on a theory originating from the Holstein Hamiltonian, we have discovered a novel way of determining the exciton coherence number, Ncoh, directly from the photoluminescence (PL) spectrum in a class of molecular assemblies known as J-aggregates1 (Fig.1a). Understanding and ultimately optimizing Ncoh is a major goal indesigning efficient solar cells since coherent transport is orders of magnitude faster than incoherent transport. We have recently applied our methods to successfully account for the photophysics of polydiacetylene chains or quantum wires2 (Fig.1b). [1]F.C. Spano and H. Yamagata, J. Phys. Chem. B 2011, 115, 5133. [2] H. Yamagata and F.C. Spano, J. Chem. Phys. 2011, 135, 054906. (a) (b) (Lecuiller, et. al., Phys Rev. B 2002 , 66, 125205.) Figure:1 a) PL spectra for linear J-aggregates with several values of Ncoh. The coherence number is directly related to the ratio of 0-0 to 0-1 line strengths. b) Calculated and measured PL line strength ratio vs the inverse square root of temperature in (red-phase) single-chain, in-situ polymerized polydiacetylene.

2. Novel Means of Determining the Exciton Coherence Number from the Photoluminescence SpectrumFrank C. Spano, Temple University, DMR 0906464 • The work supported in this Grant has fostered international collaborations with the following groups: • Richard Friend, Cavendish Laboratory, Cambridge England • David Beljonne, Universitat de Mons, Belgium • Peter Bobbert, Technische Universiteit Eindhoven • Carlos Silva, University of Montreal • Jasper Knoester, Rijksuniversiteit Groningen • Robert Silbey, MIT • Jean-Luc Bredas, Georgia Tech