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9,10-Dihydroxybenzo[ℎ]quinoline; 10-hydroxybenzo[ℎ]quinoline; ESIPT; X-ray diffraction; density functional theory calculations.

9,10-Dihydroxybenzo[ℎ]quinoline (1), a 10-hydroxybenzo[ℎ]quinoline (2) derivative, was synthesized and characterized by ¹H NMR, ¹³C NMR, UV-vis and fluorescence spectra, and single-crystal X-ray diffraction. Compound 1 possesses an intramolecular six-membered-ring hydrogen bond, from which excitedstate intramolecular proton transfer (ESIPT) takes place from the phenolic proton to the pyridinic nitrogen, resulting in a proton-transfer tautomer emission of 650 nm in dichloromethane. Its molecular geometry in the ground state has also been calculated using density functional theory (DFT) at the B3LYP/6-31G^∗∗ level and compared with its crystal structure. Results show that the optimized geometry can well reproduce the crystal structure. Furthermore, both absorption and emission spectra of 1 and 2 were calculated using time-dependent DFT (TD-DFT) calculations, and were in good agreement with the experimental results.

Kew-Yu Chen¹ Hsing-Yang Tsai¹ Wei-Chi Lin¹ Hou-Hsein Chu¹ Yu-Ching Weng¹ Chih-Chieh Chan¹

1. Department of Chemical Engineering, Feng Chia University, 40724 Taichung, Taiwan, Republic of China

Published

July 2014

Manuscript received

14 October 2013

Manuscript revised

28 January 2014

Accepted

18 February 2014