New molecular materials for hole injection: the synthesis and in situ ESR-UV/Vis/NIR spectroelectrochemistry of 2-diarylaminothiophene-based starburst compounds

Abstract

A series of 2-diarylaminothiophene-based starburst compounds 14–16 with a central triphenylamino-, benzene-, and 1,3,5-triphenylbenzene moiety, respectively, were prepared at moderate yields by a palladium-catalysed coupling reaction. Their electrochemical, optical and magnetic properties were studied with respect to their application as hole transport materials, using cyclic voltammetry and in situ ESR-UV/Vis/NIR spectroelectrochemistry. Although all prepared 2-diarylaminothiophene-based starburst compounds are structurally related, their electrochemical properties differ in their dependence on the central moiety. The number of reversible voltammetric peaks is diminished upon changing the central triphenylamino moiety of the starburst compounds to a central benzene or 1,3,5-triphenylbenzene moiety. The simultaneous multiple electron transfer as well as the location of the spins on the core moieties was detected in the oxidation of the 1,3,5-triphenylbenzene based starburst compound. The stability of the charged states increased substantially upon the incorporation of a thiophene moiety between the central moieties and the side groups.