Substituent-Dependent Photoinduced Intramolecular Charge Transfer in <i>N</i>-Aryl-Substituted <i>trans</i>-4-Aminostilbenes

The photochemical behavior of trans-4-(N-arylamino)stilbene (1, aryl = 4-substituted phenyl) in solvents more polar than THF is strongly dependent on the substituent in the N-aryl group. This is attributed to the formation of a twisted intramolecular charge transfer (TICT) state for those with a methoxy (1OM), methoxycarbonyl (1CO), or cyano (1CN) substituent but not for those with a methyl (1Me), hydrogen (1H), chloro (1Cl), or trifluoromethyl (1CF) substituent. On the basis of the ring-bridged model compounds 3−6, the TICT states for 1CN and 1CO result from the twisting of the anilino-benzonitrilo C−N bond, but for 1OM it is from the twisting of the stilbenyl-anilino C−N bond, both of which are distinct from the TICT states previously proposed for N,N-dimethylaminostilbenes.