Low-lying excited states of 4-dimethylaminobenzonitrile: Equilibrium geometries, vibrational frequencies and charge transfer character

Equilibrium geometries and vibrational frequencies of the ground and low-lying excited states of 4-(dimethylamino)benzonitrile (DMABN) are reported (6-31G * ^- basis set, ab initio RHF and CI-singles methods). The results suggest that: (i) the ground state structure is planar (C₅ symmetry); (ii) the (relaxed) locally excited state has the dimethylamino group twisted somewhat about the N-Ar bond (C₁ symmetry); and (iii) the TICT state is actually a transition state between two mirror image locally excited state structures in the gas phase, where the Me-N bonds are perpendicular to the N-Ar bond.