Photocreated metastable states in polysilanes

Hydrodynamic and molecular characteristics of organosilane copolymers of low molecular weight

Molecular hydrodynamics and light scattering measurements have been carried out in dilute solutions of polysilanes copolymers containing segments with different degrees of rotational freedom. For this purpose, three low-molecular-weight linear polydiphenylsilane copolymeric structures containing various amounts of methylhydrosilylene or methylphenylsilylene flexible units have been synthesized and studied. The molecular and hydrodynamic properties of the diphenylsilane copolymers proved to be dependent on their composition and on the chemical structure of the second co-monomer.

Ultraviolet photoinduced weak bonds in aryl-substituted polysilanes

The susceptibility of aryl-substituted polysilylenes to photodegradation by ultraviolet (UV) radiation is examined on the prototypical materials poly[methyl(phenyl)silylene] (PMPSi) and poly[(biphenyl-4-yl)methylsilylene] (PBMSi). We extend the scope of our last paper (Schauer et al 2004 Polym. Degrad. Stabil. 84 383) with the elucidation of the degradation mechanisms for two different degradation wavelengths: 266 and 355 nm. The main purpose of this paper was to study photoluminescence (PL) after major degradation, predominantly in long-wavelength range 400-600 nm, studying the disorder, dangling bonds (DBs) and weak bonds (WBs) created by the degradation process. We claim that the PL of the 500-600 nm band is related to the existence of WBs on the Si chain and originates in the σ(*)-σ exciton migration at room temperature by diffusion, free electron-hole formation, trapping in WBs and subsequent radiative recombination by tunnelling. Increase of the normalized PL 520-540 nm band after UV degradation can be then evaluated as the increase of the density of states (DOS) of WBs. The efficiency of the WB creation in PMPSi is greater for 266 nm irradiation, supporting the notion of the suppressed exciton transport compared to the less energetical photon of 355 nm, where the WB creation is lowered due to the exciton migration to longer segments and/or already existing defects. For PBMSi the WB creation kinetics for 355 nm degradation is similar to that of PMPSi. The 266 nm degradation results then support the model calculations of DB and WB reconstruction in the more rigid Si skeleton.

Vacuum-ultraviolet spectroscopy of poly(methylphenylsilylene)

The first vacuum-ultraviolet spectrum of a polysilylene (chain-type polysilane) with aromatic substituents is presented. Assignments of the absorption bands of the model compound poly(methylphenylsilylene) are based on previous experimental data and theoretical electronic band structure calculations for poly(alkylsilylenes) and on ultraviolet spectra of phenyl-containing monomers and polymers. Although aryl orbitals mix with the sigma-conjugated orbitals located along the catenated silicon backbone, some transitions are largely localized on the phenyl groups. These assignments elucidate the nature of the bonding in polysilylenes and should be useful in understanding photodegradation mechanisms and in the design of related new optical materials.