Ab Initio Study of the Electronic Spectrum of 7-Hydroxyquinoline

The electronic spectrum of 7-hydroxyquinoline has been studied by using ab initio Multi-State Multi-Reference Møller-Plesset Second-Order Perturbation Theory (MSMRMP2). The energy range up to 6.5 eV is taken into consideration. The lowest π–π* transition is calculated to have an energy of 3.65 eV in good agreement with experimental data. Several other π–π* transitions are predicted to have excitation energies of 4.93, 5.20, 5.47, and 6.08 eV. Excitations out of the highest occupied σ orbital into the lowest unoccupied π* orbitals are computed to occur at 5.28 and 6.44 eV. The π–σ* transition is predicted at 5.87 eV. The σ* orbital involved is identified as the Rydberg 3s orbital having antibonding character along the OH bond.