Abstract
It is demonstrated that alpha,beta-unsubstituted meso-positioning thienyl BODIPY is an electron deficient unit that leads to the development of ultra low optical band gap (E-g(opt) < 1 eV) pi-conjugated D-A quarterthiophene polymers. Furthermore, it is revealed that the optoelectronic, electrochemical and charge transporting properties of the resulting alpha,beta-unsubstituted meso-positioning thienyl BODIPY quaterthiophene-based polymers are alkyl side chain positioning dependent. Tail-to-tail (TT) positioning of the alkyl side chains at the two central thiophenes of the quaterthiophene segment results in lower E-g(opt), higher energy levels and increased hole mobility as compared to head-to-head (HH) positioning. Finally, even though the synthesized polymers exhibit high electron affinity, higher even than that of the fullerene derivative [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM), they present only p-type behaviour in field effect transistors (FETs) independent of the alkyl side chain positioning.