Nature of dual fluorescence in 2-(quinolin-2-yl)-3-hydroxychromone: Tuning between concurrent H-bond directions and ESIPT pathways |
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Authors: | Denis Svechkarev Vyacheslav Baumer |
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Affiliation: | a Institute for Chemistry at Kharkov V.N. Karazin National University, 4 Svobody Sq., Kharkov 61077, Ukraine b STC Institute for Single Crystals NAS of Ukraine, 60 Lenin Ave., Kharkov 61001, Ukraine |
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Abstract: | 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. |
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Keywords: | Quinoline-substituted 3-hydroxychromone ESIPT Hydrogen bond Intersystem crossing Fluorescence quenching |
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