Thiophene-silole copolymers

Silole-thiophene copolymers, with varying silole thiophene ratios from 1 2 to 1 4, have been obtained by a palladium cross-coupling reaction173, as outlined in Scheme 28. 

FIGURE 14. Plot of the bandgaps (Iif) determined from absorption edge versus silole/thiophene ratios for a series of silole-thiophene copolymers. Reproduced by permission of Wiley-VCH from Reference 45... 

Poly(2,5-silole) 7 shows a Aab of 482 nm at room temperature.24 A band gap of the polymer, if calculated with the absorption edge (650 nm), is 1.9 eV. A silole-thiophene alternating copolymer 8 can show a further decreased band gap.25 The copolymer displays a broad absorption spectrum with Aab at 648 nm in chloroform. The calculated band gap from the absorption edge is only 1.55 eV, a very small value so far reported for the synthesized SCPs. 

Tamao K, Yamaguchi S, Ito Y, Matsuzaki Y, Yamabe T, Fukushima M, Mori S (1995) SUole-containing n-conjugated systems. 3. Series of silole-thiophene cooligomers and copolymers synthesis, properties, and electronic structures. Macromolecules 28 8668-8675... 

Siloles 39 and 40 have been prepared in this way by Tamao and coworkers54 in 64 and 40% yield, respectively, the 2,5-dithienylsilole 40 being a useful monomer unit for the synthesis of thiophene-silole copolymers (see Section IV.B). 

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