Nature of dual fluorescence in 2-(quinolin-2-yl)-3-hydroxychromone Tuning between concurrent H-bond directions and ESIPT pathways

Synthesis of the quinoline-substituted 3-hydroxychromone is reported spectral and fluorescent properties of the title compound are investigated in different solvents The question of the possibility of the participation of the substituent heterocycle s nitrogen atom in H-bond formation as well as in the ESIPT process is discussed Quantum-chemical modeling provides evidence that the structure with an alternative H-bond to nitrogen is more energetically favorable and strongly prevails in solutions However our calculations together with the experimental data reveal that the excited species with the intramolecular N HO hydrogen bond type undergoes rapid radiationless deactivation This leads to a conclusion that the low-intensity dual-band fluorescence of the title compound in solutions originates from the traces of the conformation with the traditional flavonol-like H-bond to the carbonyl oxygen atom A possibility to reversibly tune the direction of the intramolecular H bond formation and thus regulate the ESIPT process pathway is demonstrated by the example of protonation/deprotonation of the title compound in a methylene chloride solution (C) 2010 Elsevier B V All rights reserved