We have used investigations of low-temperature photoluminescence and thermally stimulated luminescence to study the effect of acetophenone and pyrene dopants on the photochemical stability of poly(methylphenylsilane) (PMPS) films. We have established that pure PMPS films and acetophenone-doped PMPS films degrade on exposure to UV radiation due to breaking of Si-Si bonds followed by formation of crosslinks between the macromolecules. At the same time, pyrene inhibits degradation of PMPS to a significant extent. This proves that photoinduced breaking of the Si-Si bond can occur upon excitation of the macromolecule to the first triplet T 1 (σσ * ) state, since acetophenone sensitizes while pyrene quenches the intrinsic phosphorescence of PMPS. So the photochemical stability of PMPS can be improved by introducing a dopant which quenches triplet excitations of the macromolecule.
Introduction.Polysilanes are linear organosilicon polymers in which the backbones of the macromolecules are formed by σ-bonded silicon atoms with two added organic groups. These compounds are characterized by strong absorption in the near UV region of the spectrum, high fluorescence and charge carrier photogeneration quantum yields, high mobility of holes, and the presence of nonlinear optical properties [1-3]. The chromophores in polysilanes are segments of the macromolecular backbone within which the Si-Si σ electrons are delocalized. The segments have different lengths and are separated by conformational defects formed at inflection points in the backbone. With an increase in the number of Si atoms in the segment and accordingly an increase in its length, the energies of the excited states and the ionization potential of the segment are lowered [1,4,5].PMPS is a typical representative of the considered class of polymers. This polymer dissolves well in nonpolar solvents, and when sprinkled from solutions forms high-quality films which are used as transport or active light-emitting layers of electroluminescent diodes [6-8]. PMPS and its copolymers have been used to develop electrophotographic layers for xerography [9], recording media for data storage by the photorefractive method [10], and binders for photovoltaic devices [11]. Moreover, irradiation of PMPS with light in the band for the S 1 ← S 0 transition (from the S 0 ground state to the first excited singlet S 1 state) causes degradation of the polymer, which is enhanced as the temperature rises. Degradation begins with breaking of the Si-Si bond. Then crosslinks are formed between macromolecules, cyclic structures are formed, and when irradiated by light in air compounds are formed containing Si-O-Si, Si-H, and Si-OH bonds [1,12,13]. Therefore PMPS and its copolymers are used as photoresists for microlithography [1,12] and also as precursors in making interface microlenses [14] and forming hybrid polysilane-silica films with controllable refractive index [15].In order to improve the photogeneration and electrically conductive properties, aromatic compounds are introduced into PMPS as d...