Thiophene-silole polymers

Recent application of the nickel-catalyzed reaction with diyne 91 provides new effective access to functionalized silole derivatives 92, which are further utilized for the synthesis of silole-thiophene co-polymers (Eq.47) [84]. 

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. 

The replacement of some thiophene rings by other heteroaromatic rings, such as silole [49,50] or phosp-hole [51-53], represents an alternative solution to modulate the bandgap of PT. Thus, polymer 11 shows a relatively low value of 1.60 eV due to the low aromatic character of phosphole. Additionally, optical and electrochemical properties depend on the substitution at the phosphorus atom [51-53]. Similarly, insertion of the nonaromatic thiophene-S,S-dioxide in conjugated systems, such as 12, has been shown to produce an extension of the ir-electron delocali2ation associated with the reduction of bandgap [54—57]. 

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