Quantum Confinement Induced Collapse of a Large to a Small Radius Self-Trapped Exciton in a Permethylated Polysilane Chain

摘要

Low-temperature absorption and fluorescence spectra of a series of permethylated oligosilanes Si_nMe_(2n+2) in their all-anti form permits the identification of Si_7Me_(16) as the shortest chain capable of supporting a large-radius exciton in its relaxed lowest singlet excited state, while Si_6Me_(14) and shorter chains only carry small-radius self-trapped excitons. The following approximate one-dimensional semiconductor characteristics are derived from the data: exciton band half-width, approx 3.0 eV; lattice relaxation energy, approx 1.8 eV; and exciton-phonon coupling constant in the infinite chain, approx 0.6.