Theoretical investigation of the intramolecular hydrogen bond formation, non-linear optic properties, and electronic absorption spectra of the 8-hydroxiquinoline

The conformational stability of the 8-hydroxyquinoline was investigated by density-functional B3LYP calculations using the 6-311++G(d,p) basis set. From the potential energy scans of the internal rotations of the hydroxyl group the calculations predicted a mixture of two conformations, one with the hydroxyl hydrogen pointing to the nitrogen (α-8-hydroxyquinoline) and the other with the hydrogen pointing in the opposite direction (β-8-hydroxyquinoline). The α conformation being about 7.63 kcal/mol more stable than the β. Time-dependent density-functional theory (TD-DFT) was applied to analyze the vertical electronic absorption spectra of α-8-hydroxyquinoline. The 25 lowest excited states were calculated together with the transition dipole moments using the B3LYP/6-311++G(d,p) level of theory. The influence of the conformation on the (hyper)polarizability properties was also investigated.