Synthesis and Properties of Hybrid Organic−Inorganic Materials Containing Covalently Bonded Luminescent Polygermanes

Covalent binding of arylmethylpolygermanes into hybrid silica materials leads to substantial increases in thermal stability without degrading Ge−Ge σ-conjugation, as determined by UV−vis absorption and fluorescent emission spectroscopy. Poly(methyltrimethoxysilylphenylgermane) was prepared by ruthenium-catalyzed demethanative coupling of dimethyl(trimethoxysilylphenyl)germane, and then hydrolyzed and cured in the presence of either tetraethoxysilane (TEOS) or β-acetoxyethylsilsesquioxane (BAESSQ) to yield hybrid materials containing the polygermane linked to the matrix at every repeat unit. Thermal stability of the bulk hybrid materials was examined by TGA, and films were examined by UV−vis spectroscopy following thermal treatment and photochemical irradiation. Conjugation of the Ge−Ge chains is maintained to 380 °C under nitrogen in the case of the BAESSQ-derived hybrids, but only 200 °C in air. The photolytic stability of the hybrid films is greater than the parent poly(methylphenylgermane), but the gains are less dramatic. A model is proposed in which anchoring each germanium in the polymer chain to the silica matrix reduces mobility of germyl radicals produced by both thermolysis and photolysis, leading to efficient recombination to restore the Ge−Ge chains under nitrogen. On the other hand, germylene intermediates generated only during photolysis are more reactive and can combine irreversibly with Si−O−Si bonds or residual SiOH groups in the silica matrix, leading to faster photolytic degradation of the conjugated Ge−Ge chains, even under nitrogen.