7,9-Diiodobenzo[h]quinolin-10-ol (1), a benzo[h]quinolin-10-ol derivative, was synthesized and characterized by single-crystal X-ray diffraction. The crystal belongs to monoclinic, space group P2(1)/c, with a = 7.3765(16), b = 12.616(2), c = 12.881(2) angstrom, alpha = 90 degrees, beta = 93.420(16)degrees, and gamma = 90 degrees. Compound 1 possesses an intramolecular six-membered-ring hydrogen bond, from which excited-state intramolecular proton transfer takes place, resulting in a proton-transfer tautomer emission of 628 nm in cyclohexane. Moreover, the geometric structures, frontier molecular orbitals and the potential energy curves for 1 in the ground and the first singlet excited state were fully rationalized by density functional theory (DFT) and time-dependent DFT calculations.