Intramolecular Charge Transfer with N,N-Dialkyl-4-(Trifluoromethyl)anilines and 4-(Dimethylamino)benzonitrile in Polar Solvents. Investigation of the Excitation Wavelength Dependence of the Reaction Pathway

suitable for an investigation of the excitation wavelength dependence of the intramolecular charge transfer reaction.For DPrCF3 in MeCN, the same Φ (ICT)/Φ(LE) is found for excitation in the S1 or in the S2 manifold.A similar result is obtained with DMABN in tetrahydrofuran.From these experiments it is concluded that for DPrCF3 and DMABN the intramolecular charge transfer reaction follows an adiabatic pathway.After excitation to a Franck-Condon Sn(FC) state, the electron donor/acceptor molecules first undergo ultrafast internal conversion to the relaxed LE(S 1 ) state, from which precursor the reaction proceeds to the ICT state.Experimental evidence for a nonadiabatic ICT reaction pathway, going directly from S 2 (FC) via an S 2 /S 1 conical intersection to the LE and ICT state, is not found.This pathway would lead to an enhancement of the ICT population, i.e., to an increase in Φ (ICT)/Φ(LE), as compared with the adiabatic LE → ICT reaction.