Computation and spectroelectrochemistry as complementary tools for the study of electrochemically induced charged defects in 4-[bis(4-methylphenyl)amino]phenyl oligothiophenes as model systems for hole-transporting materials

The in situ electronic absorption and Fourier transform Raman scattering spectra recorded during the electrochemical oxidation of two alpha,alpha'-end-capped 4-[bis(4-methylphenyl)amino]phenyl oligothiophenes with three and four thiophene rings are reported. We have characterized a radical cation and a dication species in the trimer and up to a radical trication in the tetramer. The electronic and the Raman spectra have been interpreted and assigned with the final goal of obtaining structural information about the contribution of the bis(4-methylphenyl)amino groups, the innermost phenyl rings, and the central thienyl chain length to the stabilization of the electrochemically induced charged defects. The experimental data have been supported by theoretical calculations in the framework of the density functional theory. The charged defects can be viewed as models of hole carriers or photoexcitons in real devices.