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Author: search.filters.author.Kerdpol, KhanitthaSubject: search.filters.subject.B3LYP

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    The effect of protic solvents on the excited state proton transfer of 3-hydroxyflavone: A TD-DFT static and molecular dynamics study
    (2018-02-01)
    Salaeh, Rusrina
    ;
    Prommin, Chanatkran
    ;
    Chansen, Warinthon
    ;
    Kerdpol, Khanittha
    ;
    Daengngern, Rathawat
    The effect of intermolecular hydrogen bonding played by protic solvents (ammonia, methanol and water) on the excited state proton transfer (ESPT) reaction of 3-hydroxyflavone (3HF) was theoretically investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT). The formation of intermolecular hydrogen bond induced by protic solvents indicates that the intramolecular hydrogen bond may be interrupted in favor of a complex causing low quantum yield of keto emission and exhibiting dual emission (both enol and keto) in experiment. The strengthening of intermolecular hydrogen bond in the S<inf>1</inf> state has been confirmed by the red-shift of IR vibrational spectra and shorter bond distances involving proton transfer (PT) process in comparison with those of the S<inf>0</inf> state. From potential energy curves (PECs) of PT coordinate, PT process is likely to proceed in S<inf>1</inf> state and PT in 3HF(NH<inf>3</inf>) occurs more easily than those of 3HF(CH<inf>3</inf>OH) and 3HF(H<inf>2</inf>O) due to its lower barrier. Moreover, on-the-fly dynamics simulations of all complexes were carried out to provide the detailed information on the PT mechanism. The dynamic results show that ESPT process of 3HF with protic solvent takes place through intermolecular hydrogen bond with slower PT time (259, 117 and 104 fs for 3HF(NH<inf>3</inf>), 3HF(CH<inf>3</inf>OH) and 3HF(H<inf>2</inf>O), respectively) than that of 3HF (76 fs) via intramolecular hydrogen bond. Furthermore, the ultrafast PT time is found to be nicely correlated with polarity of solvent and PT probability is also anti-correlated with PT barrier.
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    Theoretical study on influence of geometry controlling over the excited-state intramolecular proton transfer of 10-hydroxybenzo[h]quinoline and its derivatives
    (2017-08-01)
    Chansen, Warinthon
    ;
    Salaeh, Rusrina
    ;
    Prommin, Chanatkran
    ;
    Kerdpol, Khanittha
    ;
    Daengngern, Rathawat
    A structural modification on quinoline as a proton donor of 10-hydroxybenzo[h]quinoline (HBQ) giving different HBQ derivatives greatly affects their photophysical properties. In this study, the excited-state intramolecular proton transfer (ESIPT) reactions of HBQ and its derivatives with different geometries have been systematically investigated using DFT and TD-DFT at B3LYP/TZVP. Calculated absorption and emission spectra are used to describe the photophysical changes in which the absorption spectra of HBQ derivatives are blue-shifted compared with that of HBQ while their emission spectra are blue-shifted except those of 3,4-dihydro indene[1,2-b]pyrrole-8-ol (IPRO) and 2-(4H-pyrrol-2-yl)phenol (PRP) compounds with different proton donor and connecting moiety are red-shifted. From results of potential energy curves along the proton transfer (PT) coordinate, PT is favorable in the excited-state but not in the ground state. On-the-fly dynamics simulations in the excited-state are further employed to determine reaction mechanisms and the time evolution of PT. The ESIPT process easily occurs in most of the compounds except the IPRO with much high PT barrier. The ESIPT times in most compounds take place within 100 fs and PT probability is nicely anti-correlated with the PT barrier. Thus, the geometry changes alter the electronic spectra but do not affect ESIPT of HBQ derivatives. Moreover, once the PT is complete, the internal conversion is initiated by twisted skeleton, leading to lower intensity of tautomer emission.