The effect of Si skeleton structures of poly(methyl-n-propylsilane) (PMPrS) on the electron delocalization has been studied in polar liquid matrices by the low-temperature pulse radiolysis technique over a wide range of temperatures. PMPrS was revealed to have a rigid rodlike Si main chain in the polar matrix at low temperature (<110 K) despite having a random coil structure at the higher temperature. The value of the Stokes shift decreased consecutively with decreasing temperature and reached 0 below 110 K, indicating the extremely lower relaxation energy of an exciton state on a a-conjugated Si-chain than that (0.08 eV) at 300 K. The relaxation dynamics of radical anions were also investigated by the pulse radiolysis technique. An increase in the molar extinction coefficients of PMPrS- from 1.1 x 10(5) to 1.9 x 10(5) M-1 cm(-1) was observed with decreasing temperature from 298 to 193 K, reflecting an increase in the degree of delocalization of excess electrons.