Electronic spectroscopy and photophysics of 2-(N-methyl-N-isopropylamino)-5-cyanopyridine and related compounds

In polar solvents, dual fluorescence is observed for three electron donor acceptor molecules, consisting of the m-cyanopyridine electron acceptor and one of three slightly different N,N-dialkylamino donor groups: N-methyl-N-isopropyl, N,N-diethyl, and N,N-dimethyl. A low energy anomalous emission is assigned to a twisted intramolecular charge transfer (TICT) state. Kinetic and steric factors account for variations of the TICT vs. primary emission intensity ratio in the three compounds. Comparison with the TICT paradigm, N,N-dimethylaminobenzonitrile is also provided. In alcohol solutions, relative enhancement of the TICT fluorescence, as well as a fast radiationless process from the initially excited state are observed. Possible sources of these phenomena are discussed.