SITE-SELECTIVE FLUORESCENCE STUDIES ON POLYSILYLENES

Low temperature site-selective fluorescene spectroscopy was performed on poly (di-n-hexylsilyene) and poly (methyl- phenylsilylene), both present as solid film and matrix-isolated in a 2-MTHF glass. The experiments confirm that absorption and emission are exciton processes controlled by disorder arising from the length distribution of ordered chain segments that depends on the morphology of the sample. Upon exciting into the center portion of the density of states (DOS), excitations relax to a common occupational density of states mapped by the inhomogeneously broadened fluorescence spectrum. Upon tail state excitation, resonant emission shifting linearly with the excitation energy becomes progressively important. Coupling to both phonons and vibrations of the chain is very weak. The experiments are in quantitative accord with the results of Monte Carlo computer simulations for the random walk of excitations in an array of hoping sites featuring a Gaussian distribution of site energies. The existing analogy between exciton and charge transport suggests that site-selective fluorescence studies are a useful tool also for delineating the key features of charge carrier motion in polymeric systems.