Electron energy loss and DFT/SCI study of the singlet and triplet excited states of aminobenzonitriles and benzoquinuclidines: Role of the amino group twist angle

Spectroscopic consequences of varying the twist angle of the amino group iri aminobenzonitrile systems in the electronic ground state are investigated by applying electron energy loss (EEL) spectroscopy and density functional theory to 4-N,N-dimethylaminobenzonitrile (DMABN), 4-N,N-dimethylamino-3,5-dimethylbenzonitrile (MMD), benzoquinuclidine (BQ), and 6-cyanobenzoquinuclidine (CBQ). A number of singlet and triplet excited states was observed and assigned with the help of DFT/SCI theory. The results characterize the gas-phase spectroscopy of the molecules and verify to within 0.3 eV the predictive power of DFT/SCI theory for vertical states over a wide range of twist and pyramidalization angles. The amino group configuration in the relaxed charge-transfer state of dual fluorescent aminobenzonitriles in solution cannot be directly deduced from the present data, however.