Electronic excitation transport on isolated, flexible polymer chains in the amorphous solid state randomly tagged or end tagged with chromophores

Abstract

The transport of electronic excitations among chromophores which are randomly tagged or end tagged on finite flexible polymer chains in the amorphous solid state is described. First, the previously reported first order cumulant expansion treatment of excitation transport among chromophores randomly distributed in solution is extended to treat finite volume systems with nonrandom chromophore distributions. The method is demonstrated by considering chromophores randomly distributed in a finite sphere. The results are in good agreement with a previous treatment of this problem using a density expansion. The probability of finding the initially excited chromophore, still excited at time t, Gs(t), is calculated. Gs(t) is directly related to fluorescence depolarization and other observables. Gs(t) is then calculated for a finite flexible polymer chain in a polymer blend which is randomly tagged in low concentration with chromophores. The method permits any form of the polymer pair correlation function to be used. A specific model, a Gaussian segment distribution function, is employed, and an explicit time domain expression is obtained. This expression is compared to previous theoretical treatments which did not contain adequate descriptions of the pair correlation function. Greatly improved agreement with experiment is obtained. Excitation transfer on an end tagged coil is a limiting case of the random tagged problem. In addition, the energy transport aspect of the end tagged problem is treated exactly and the two approaches are compared.