Alternating Donor/Acceptor Repeat Units in Polythiophenes. Intramolecular Charge Transfer for Reducing Band Gaps in Fully Substituted Conjugated Polymers

This paper describes a method to limit the band gap widening that occurs in fully substituted conjugated polymers. This is done by constructing step growth [AB] polymers where the A-units are electron rich and the B-units are electron deficient. The thiophene-based polymers were prepared by modified Stille polymerizations using Pd(0)/CuI catalyst systems in which aryldibromides were coupled with aryldistannanes. The donor units were N,N‘-(bis-tert-butoxycarbonyl)-3,4-diaminothiophene, N,N‘-(bis-tert-butoxycarbonyl)-N,N‘-(dimethyl)-3,4-diaminothiophene, 3,4-diaminothiophene, or 3,4-dialkoxythiophenes while the acceptor units were 3,4-dinitrothiophene, 3,4-(N-n-butylimido)thiophene, or 3,4-diketone-containing thiophenes. The optical spectra showed λmax values ranging from 400 to 676 nm (solution) and 400−768 (film) for these fully substituted polythiophenes, consistent with significant decreases in the band gaps. Intramolecular charge transfer character between the consecutive units explained the lowering o...

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