Charge transfer in aminobenzonitriles: do they twist?

Ab initio electronic structure calculations have been performed to characterize the charge-transfer process in benzonitrile, 4-aminobenzonitrile and 4-dimethylaminobenzonitrile. The HF, CIS, CASSCF and CASPT2 methods have been employed. Geometry optimization of the charge-transfer state predicts a planar configuration with bent CN group. The results suggest that bending of the cyano group rather than twisting of the amino group is the intramolecular motion which is responsible for the stabilization of the charge-transfer state in aminobenzonitriles.