Synthesis and characterization of poly(triarylamine)s containing isothianaphthene moieties

We report the synthesis, characterization, and properties of a new class of hole-transport dyes, poly(dithienylisothianaphthene phenyldiamine)s (poly-DTITNPDs). These polymers are characterized by the presence of a low band gap isothianaphthene (ITN) and triarylamine units in the main chain. A modified Ullmann polycondensation reaction using a phase-transfer catalyst was utilized to prepare these polymers. The optical, thermal, and electrochemical properties were studied and compared to those of poly(triphenyldiamine ether) without having an ITN group and poly(dithienylisothianaphthene) without having triarylamine groups in the main chain. The new polymers, reported here, exhibit improved thermal stability and higher glass-transition temperatures. The incorporation of ITN group into the main chain of a polytriarylamine causes an appreciable lowering of the band gap energy up to 1.6 eV. This results in light-harvesting hole-transport dyes having less mismatch with the solar spectrum. Moreover, these polymers exhibit reversible redox behavior and possess HOMO values of about -4.7 eV and LUMO values of about -2.9 eV.