Vibrational Effects in Molecular Exciton Motion Along a Polymer

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Abstract
Two aspects of the effects of molecular vibrations on exciton motion are considered: First is the reversible evolution of an electronically excited state of a system of molecules, in each of which many vibrational excitations are possible upon electronic excitation. Vibrational structure of the ground state is ignored. The reversible, or coherent, propagation is found to depend on the parameter 2πν2δ—1, where ν2 is the intermolecular coupling energy of individual vibronic levels, and δ is the spacing of vibrational levels. Second is the irreversible effect of vibrational relaxation in individual molecules through interaction with the solvent. The result of a heuristic treatment is that simple diffusive motion occurs if the relaxation time is much smaller than 2πhδ—1, and the diffusion coefficient is calculated. Throughout, we deal with an infinite, linear array of molecules.