Electronic structure of σ-conjugated system of polysilanes studied by electron beam pulse radiolysis

The Si skeleton structure of poly(methyl-n-propylsilane) (PMPrS) was studied in polar and non-polar liquid matrices as a function of the temperature. PMPrS was revealed to have a rigid rod-like Si main chain in the polar matrix at low temperature (<110 K) in spite of having a random coil structure in the same liquid at the higher temperature. The value of Stokes shift consecutively decreases with the drop of temperature and reaches 0 below 110 K, indicating the extremely low relaxation energy of an exciton state on a σ-conjugated Si-chain though that was observed at ca. 0.5-1 eV at 300 K. The relaxation processes of radical cations and anions were also studied by a low temperature pulse radiolysis technique. An increase in the molar extinction coefficients of transient absorption bands was observed for anions with decreasing temperature, reflecting an increase in the density of states which were attributed to a polaron state on a Si main chain