PHOTOCREATED METASTABLE STATES IN POLYSILANES

Photocreated metastable states in organopolysilane (PSi) solids are ob served using the electron-spin-resonance (ESR) technique. Two types of light-induced ESR (LESR) spectra are found depending on the excitatio n photon energy. These two types of LESR centers are annihilated by th ermal annealing. Based on a first-principle electronic calculation, th e origins of these LESR centers have been discussed. The lowest photoe xcitation (approximately 3.5 eV) in PSi induces the Si skeleton stretc hing forces, which creates a weak bond (WB) in several places of the S i skeleton. Electronically, this WB acts as a self-trapping center for the photoexcited sigma electron. The other higher photoexcitation (ov er 4.8 eV) causes side-pendant dissociation, which creates a dangling bond (DB) and causes the localized midgap state. The four lines found in the higher-energy excitation are considered to arise from hyperfine interaction between this DB electron and a sodium impurity nucleus.