Dynamics of positive charge carriers on Si chains of polysilanes

The transient absorption of radical cations of a variety of substituted polysilanes is discussed quantitatively in terms of the molar extinction coefficient and oscillator strength by nanosecond pulse radiolysis. Oxygen -saturated polysilane solutions in benzene exhibit a strong transient absorption band ascribed to the polysilane radical cation. The transient species react with N,N,N,N-tetramethyl-p-phenylenediamine (TMPD) to produce TMPD radical cations. On the basis of the molar extinction coefficient of the TMPD radical cation, the molar extinction coefficients for the radical cations of polysilanes are found to increase in the range 3.3 x 10(4) to 2.0 x 10(5) M(-1) cm(-1) with increasing polymer segment length. The stepwise increase in the total oscillator strength with an increase in the number of phenyl rings directly bonded to the Si skeleton suggests the delocalization of the positive polaron state and/or the SOMO state over the phenyl rings, indicating the importance of phenyl rings in intermolecular hole transfer processes.