Poly(diaryl)stannanes:  Influence of Substituents on the <i>σ</i>−<i>σ</i>* Transition Energy

Abstract

Poly(diaryl)stannanes were prepared by the dehydropolymerization of secondary hydrostannanes Ar 2 SnH 2 with dimethylzirconocene catalyst. At room temperature, H(Ar 2 Sn) n H polystannanes (Ar = p - t Bu-C 6 H 4, p - n Hex-C 6 H 4, o -Et-C 6 H 4, o -Et- p - n BuO-C 6 H 3, p - n BuO-C 6 H 4, p -(Me 3 Si) 2 N-C 6 H 4 ) exhibit λ max values attributed to σ → σ * transitions in the range 430−506 nm. These values vary according to the polymer molecular weights and are independent of temperature between −20 and 90 °C. A sample of poly[bis( o -ethyl- p - n butoxylphenyl)]stannane exhibits a strong UV−vis absorption at 506 nm (tailing to ca. 550 nm), which corresponds to the smallest band gap yet observed for a group 14, σ-conjugated polymer. The H(Ar 2 Sn) n H polystannanes undergo photodecomposition in solution to give a mixture of the cyclo -hexamer and the cyclo -pentamer. Thermal gravimetric analyses 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 °C, under both nitrogen and air. The H(Ar 2 Sn) n H polystannanes undergo clean thermal decompositions to elemental tin (under nitrogen) or tin oxide (under oxygen or air), as shown by bulk pyrolysis.