Electron transfer between molecules randomly distributed in a glass

Publisher Website
Google Scholar
Abstract
A theoretical and experimental study of electron transfer from an optically excited donor to randomly distributed acceptors in a glassy medium is presented. The influence on time dependent observables of an electron transfer rate which is dependent on the orientation of donor and acceptors in a system with random distance and angular distributions is examined. It is formally proven that an angular dependent electron transfer rate will affect the ensemble averaged functional form of the time dependence of donor emission. Calculations based on models of P orbital–P orbital and P orbital–S orbital angular overlap factors demonstrate that only at short time (less than a few hundred picoseconds) and high concentrations of acceptors does the time dependence deviate from that predicted by the angle independent Inokuti–Hirayama theory. At longer times (>1 ns) angle averaged electron transfer parameters can be extracted from time dependent data. Experimentally, the system pentacene (donor) and duroquinone (acceptor) in sucrose octa-acetate glass is examined. Excitation of pentacene to its first singlet state initiates the electron transfer which is monitored by observing the time dependence of fluorescence emission. The transfer parameters, R0 and a, are extracted from the time dependent curves and are used to reproduce the results of fluorescence quenching measurements on the same system. Values of R0=14.3 Å and a=0.35 Å are obtained.