Poly(di-n-hexyl-silane) in solid solutions: Experimental and theoretical studies of electronic excitations of a disordered linear chain

Abstract

The results of a study of the electronic structure and energy transfer dynamics of poly(di-n-hexyl-silane), representative of a large class of conjugated polymers, in glassy solution at low temperature are reported. Optical excitation at ca. 3500 Å yields a Frenkel exciton with possibly some small admixture of charge transfer states. The exciton is only weakly coupled to nuclear motions and small polaron effects are absent except for a slight expansion in the direction perpendicular to the chain axis on excitation. The excitation is localized by a continuous disorder distributed along the chain and apparently not by a lumped disorder in which segments of essentially perfectly ordered regions are separated by defects. The results are consistent with an exciton bandwidth of 4.4 eV. Energy transport between localized states can be understood in terms of a simple kinetic model which permits simulation of results from fluorescence and hole-burning experiments. A novel mechanism of hole burning occurring in one-dimensional disordered systems and a method to extract the range of energy transfer from fluorescence data is presented. A conformational change on the length scale of a few Si–Si bonds is predicted to occur during the phase transition.