Conformational relaxation of sigma-conjugated polymer radical anion on picosecond scale

We report the conformational relaxation of poly[bis(p-n-butylphenyl)silane] (PBPS) radical anion measured by near-ultraviolet-enhanced picosecond pulse radiolysis in tetrahydrofuran solutions. The peak shift and increase in optical density of the transient photoabsorption spectra were investigated by kinetic analysis including reactions of PBPS with solvated/presolvated electrons, peak extraction protocol, and diffusion theory, demonstrating the correspondence in the rate constant (5+/-1x10(2) ps) between the peak shift and increase in oscillator strength. The results were examined by density functional theory and molecular dynamics simulations, where the modeled oligosilane radical anion shows more planner conformation relative to its neutral state and a relaxation time of 8 ps. The difference of the time scale is discussed from the viewpoints of actual experimental factors. To the best of our knowledge, this is the first report on the direct observation of the conformational dynamics of rodlike sigma-conjugated polymer: PBPS radical anion.