Dual fluorescence and fast intramolecular charge transfer with 4-(diisopropylamino)benzonitrile in alkane solvents

Dual fluorescence and fast intramolecular charge transfer (ICT) is observed with 4-(diisopropylamino)benzonitrile (DIABN) in alkane solvents. The rate constant ka for the reaction from the locally excited (LE) to the ICT state has a value of 3.4×1011 s−1 in n-hexane at 25°C, with an activation energy Ea of 6 kJ mol−1. Efficient intersystem crossing with a yield of 0.94 takes place from the ICT state. With 4-(dimethylamino)benzonitrile, in contrast, dual fluorescence is not observed in alkanes. The charge transfer reaction of DIABN is mainly favoured by its small energy gap ΔE(S1,S2), in accordance with the PICT model for ICT in aminobenzonitriles.