α,β-Unsubstituted meso-positioning thienyl BODIPY: a promising electron deficient building block for the development of near infrared (NIR) p-type donor–acceptor (D–A) conjugated polymers

Abstract

It is demonstrated that α,β-unsubstituted meso-positioning thienyl BODIPY is an electron deficient unit that leads to the development of ultra low optical band gap (E^opt_g < 1 eV) π-conjugated D–A quarterthiophene polymers. Furthermore, it is revealed that the optoelectronic, electrochemical and charge transporting properties of the resulting α,β-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^opt_g, 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-C₇₁-butyric acid methyl ester (PC₇₁BM), they present only p-type behaviour in field effect transistors (FETs) independent of the alkyl side chain positioning.