A TDDFT study on the singlet and triplet excited-state hydrogen bonding and proton transfer of 10-hydroxybenzo[h]quinoline (HBQ) and 7,9-diiodo-10-hydroxybenzo[h]quinoline (DIHBQ)

The singlet and triplet excited state as well as the influence of an iodine on the steady-spectra of 10-hydroxybenzo[h]quinoline (HBQ) and 7,9-diiodo-10-hydroxybenzo[h]quinoline (DIHBQ) were investigated using theoretical approach. For the HBQ and DIHBQ, only enol conformation exists in the singlet excited state, whereas there are two hydrogen bonded conformations in the triplet excited state: enol- and keto-tautomer conformation. The enol phosphorescence peak of HBQ which has not been detected in experiments is at 669 nm. The phosphorescence spectrum of DIHBQ (λmax = 692 nm) may be the enol phosphorescence, which was assigned as keto-tautomer phosphorescence in the previous study.