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 k(a) for the reaction from the locally excited (LE) to the ICT state has a value of 3.4 x 10(11) s(-1) in n-hexane at 25 degrees C, with an activation energy E-a of 6 kT 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 Delta E(S-1,S-2), in accordance with the PICT model for ICT in aminobenzonitriles. (C) 2000 Elsevier Science B.V. All rights reserved.