Do twisting and pyramidalization contribute to the reaction coordinate of charge-transfer formation in DMABN and derivatives?

The dual fluorescence spectra of Various model compounds of DMABN varying i n acceptor strength are reported. Dual fluorescence occurs irrespective of whether the more allowed L-1(a)-type state is situated above or below the L -1(b)-type state. Chemical bridging of the dimethylamino group makes the ch arge-transfer (CT) fluorescence band disappear in both cases. Pyramidalizat ion effects are investigated using quantum-chemical modelling. The ionizati on potential of the dimethyl-amino donor group strongly increases with pyra midalization although the observed CT fluorescence is little affected. It i s concluded that both twisting and 'anti-pyramidalization' (rehybridization to sp(2)) are important to explain the emission properties of the CT state . (C) 2000 Elsevier Science B.V. All rights reserved.