The Use of Cyclopenta[2,1-b;3,4-b ']dithiophene Analogues for the Development of Low-Bandgap Materials

This paper presents the synthesis and characterization of low-bandgap materials based on cyclopenta[1,2-b;3,4-b′]dithiophene (CPDT). An array of electron-poor monomers is synthesized and used to prepare homo- and alternating donor-acceptor copolymers. This yields polymers with low bandgaps (E g = 1.12-1.23 eV) and broad light absorption (400-1100 nm). The influence of the electron-withdrawing substituent and the donor material on the polymer properties is studied. It is demonstrated that the low bandgap is not a result of intramolecular charge transfer, but of a transition localized in the electron-poor CPDT monomer. The bandgap can be correlated with the substituent on the CPDT monomer and is relatively independent of other parameters, resulting in materials with an easily tunable bandgap. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.status: publishe