Comment on "Pseudo-Jahn-Teller and TICT-models: a photophysical comparisonof meta-and para-DMABN derivatives" [Chem. Phys. Lett. 305(1999)8] - The PICT model for dual fluorescence of aminobenzonitriles

Due to the larger admixture of charge transfer (CT) in the intramolecular c harge transfer (ICT) state than in the locally excited (LE) state of dual f luorescent molecules such as 4-(dimethylamino)benzonitrile, the radiative r ate constant k'(f)(ICT) is smaller than k(f)(LE), irrespective of the ICT m olecular structure. The validity of the TICT or PICT model can therefore no t be tested with these data. The absence of dual fluorescence for 4-(methyl amino)benzonitrile, 3-(dimethylamino)benzonitrile and two dicyano-N,N-dimet hylanilines, which cannot be explained by the TICT hypothesis, is caused by their large energy gap Delta E(S-1,S-2), which prevents the ICT state from becoming lower in energy than LE. (C) 2000 Elsevier Science B.V. All right s reserved.