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 influences of heavy-atom effect are investigated using theoretical approach. ► The enol phosphorescence peak of HBQ (669 nm) is not found in the previous study. ► The phosphorescence peak of the DIHBQ (735 nm) may be enol phosphorescence.