Excited charge transfer states in 4-aminopyrimidines, 4-(dimethylanilino)pyrimidine and 4-(dimethylamino)pyridne Original Research Article

This paper presents a comparative study of the photoinduced electron transfer in a series of donor-acceptor compounds and their hydrogen-bonded complexes in solution. 4-(Dimethylamino) pyridine III, similarly to 4-(dimethylamino) pyrimidine I and 4-(dimethylamino)-5-methylpyrimidine II and contrary to 4-(N,N-dimethylanilino)pyrimidine IV, shows dual luminescence in a sufficiently polar and mobile environment. The results of steady-state and kinetic investigations as well as quantum chemical calculations of I–III fit well into the twisted intramolecular charge transfer (TICT) state model. On the other hand, the results suggest an enhanced planarity of the ICT fluorescent state of IV. INDO/S calculations confirm the large probability of the allowed radiative transitions in the latter compound. Photophysics of all the compounds under study is modified by hydrogen bonding: fluorescence quantum yields are strongly reduced in the presence of alcohols.