Structures and Electronic States of Permethyloligosilane Radical Ions with All-Trans Form Sin(CH3)2n+2(±) (n = 2-6): A Density Functional Theory Study.

Abstract

Hybrid density functional theory (DFT) calculations have been carried out for the radical cation and anion of permethyloligosilane Sin(CH3)2n+2(±) (n = 2-6) to elucidate the electronic structures at ground and low-lying excited states, and the results were compared with the corresponding experimental values. In particular, the assignment of electronic transition appeared at near-IR and visible regions, which is strongly correlated to hole and electron conductivity, and was carried out on the basis of time-dependent DFT calculation. The structure of oligosilane was generated at 300 K by direct PM3 molecular dynamics calculations, and then the geometry was fully optimized at the DFT(B3LYP)/6-311+G(d,p) level. It was found that the hole in the radical cation and the electron in the radical anion of oligosilane are delocalized over the Si skeleton. The proton-hyperfine coupling constants calculated were in good agreement with those obtained by an electron spin resonance experiment. It was also found that the g-anisotropy of the radical anion was significantly larger than that of the radical cation. The IR bands of radical ions were assigned on the basis of theoretical calculations.