Poly(diaryl)stannanes: Influence of substituents on the sigma-sigma* transition energy

Poly(diaryl)stannanes were prepared by the dehydropolymerization of seconda ry hydrostannanes Ar2SnH2 with dimethylzirconocene catalyst. At room temper ature, H(Ar2Sn)(n)H polystannanes (Ar = p-Bu-t-C6H4, p-(HeX)-He-n-C6H4, o-E t-C6H4, o-Et-p-(BuO)-Bu-n-C6H3, p-(BuO)-Bu-n-C6H4, p-(Me3Si)(2)N-C6H4) exhi bit lambda(max) values attributed to sigma --> sigma* transitions in the ra nge 430-506 nm. These values vary according to the polymer molecular weight s and are independent of temperature between -20 and 90 degrees C. A sample of poly[bis(o-ethyl-p-nbutoxylphenyl)]stannane exhibits a strong UV-vis ab sorption at 506 nm (tailing to ca. 550 nm), which corresponds to the smalle st band gap yet observed for a group 14, sigma-conjugated polymer. The H(Ar 2Sn)(n)H polystannanes undergo photodecomposition in solution to give a mix ture of the cyclohexamer and the cyclo-pentamer. Thermal gravimetric analys es for the polymers suggest that H(Ar-2-Sn)(n)H polystannanes are thermally stable and have onset temperatures for thermal decomposition in the range 180-320 degrees C, under both nitrogen and air. The H(Ar2Sn)(n)H polystanna nes undergo clean thermal decompositions to elemental tin (under nitrogen) or tin oxide (under oxygen or air), as shown by bulk pyrolysis.