Proton-transfer tautomerism in 10-hydroxybenzo [h] quinolines: Heavy atom effects and non-hydrogen-bonded photorotamer formation in 77 K glassy matrixes

The low-lying triplet states of 10-hydroxybenzo [h] quinolines and its halogenated derivatives 7,9-diiodo-10-hydroxybenzo [h]- quinoline (DIHBQ) in an excited-state intramolecular proton-transfer (ESIPT) process are investigated. Results show that in addition to the protic-solvent perturbation photoinduced breakage of the intramolecular hydrogen bond in 3-hydroxyflavones played a role in the prohibition of ESIPT reaction in 77 K methylcyclohexane glassy matrixes.