Theoretical study of the low-lying excited states of ABCO, DABCO and homologous cage amines Original Research Article

The electronic spectra of 1-azabicyclo[2.2.2]octane (ABCO), 1,4-diazabicyclo[2.2.2]octane (DABCO), and their [1.1.1] and [3.3.3] congeners have been studied at the ab initio level using the symmetry adapted cluster configuration interaction method. A comprehensive theoretical prediction of the discrete excitation spectra, up to the HOMO → 5s transition, is presented. All the low-lying singlet and triplet electronic states of these symmetric cage amines are found to have essentially Rydberg nature and originate from excitations out of the n-type molecular orbitals. The theoretical results correlate with the available spectroscopic data satisfactorily and provide quantitative support to a number of experimental assignments based on REMPI and MCD measurements.