Electron−Phonon Coupling in Phenyleneethynylene Oligomers: A Nonlinear One-Dimensional Configuration-Coordinate Model

Abstract

In many conjugated polymers, coupling of the torsional motions to the electronic excitation plays a major role in the spectroscopy and photophysics. In a recent paper [J. Phys. Chem. B 2006, 110, 18844], we developed a multidimensional exciton model of electron−torsion coupling that accounts for a number of unusual features in the spectroscopy of poly(phenyleneethynylene). This paper reduces that multidimensional exciton model to a one-dimensional configuration-coordinate (CC) model to facilitate interpretation of the spectroscopy and to allow extension to more complex systems. Because the CC model is derived from a more exact multidimensional model, the approximations inherent in the CC model can be examined quantitatively. The CC model accurately accounts for the line shapes in absorption and emission and the evolution of those shapes with oligomer length. Both fully anharmonic torsional potentials and nonlinear coupling are needed to predict these properties. In addition, the entropic contributions in ...