Structural modelling of optical and electrochemical properties of 4-aminodiphenylamines – optoelectronic studies on a polyaniline repeating unit

Amino-diphenylanilines and their planarized and twisted model compounds have been investigated by steady state and time-resolved absorption and emission, as well as by spectroelectrochemistry. These polyaniline model compounds show that the observation of excited states with full charge separation is linked to molecular twisting where the diaminobenzene is the donor and the phenyl group the acceptor. The observable charge transfer fluorescence shows the characteristic features of twisted intramolecular charge transfer (TICT) excited states, i.e. forbidden emissive properties and strong solvatochromic red shift. The transient absorption spectrum of the TICT state matches the ground state absorption spectrum of the electrochemically produced radical cation of the molecule. This is the first example where excited-state properties of the neutral and ground state properties of the radical cation are directly linked.