• Bulletin of the Korean Chemical Society
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• 제33권5호
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• pp.1561-1565
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• 2012

The structures of the four lowest alanine conformers, along with their radical cations and the effect of ionization on the intramolecular proton transfer process, are studied using the density functional theory and MP2 method. The energy order of the radical cations of alanine differs from that of the corresponding neutral conformers due to changes in the basicity of the $NH_2$ group upon ionization. Ionization favors the intramolecular proton transfer process, leading to a proton-transferred radical-cation structure, [$NH_3{^+}-CHCH_3-COO{\bullet}$], which contrasts with the fact that a proton-transferred zwitterionic conformer is not stable for a neutral alanine in the gas phase. The energy barrier during the proton transfer process is calculated to be about 6 kcal/mol.

• Bulletin of the Korean Chemical Society
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• 제12권4호
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• pp.441-444
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• 1991

The intramolecular proton transfers of 2-hydroxy-4,5-naphthotropone in room temperature solutions are studied using static and time-resolved absorption and emission spectroscopy. Dual normal and tautomer fluorescence is observed in ethanol solution, while only the tautomer fluorescence is observed in cyclohexane solution. The fluorescence lifetimes and quantum yields in ethanol and cyclohexane solutions indicate that in hydrocarbon solvents, rapid intersystem crossing competes with proton transfer in the first excited singlet state. Transient absorption spectra and kinetics indicate that proton transfer also undergoes in the first triplet state with a transfer time of ∼ 3 ns. No transient absorption from the tautomer ground state indicates a rapid back proton transfer in the ground state.

• Bulletin of the Korean Chemical Society
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• 제22권12호
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• pp.1407-1409
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• 2001

• Bulletin of the Korean Chemical Society
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• 제24권11호
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• pp.1675-1679
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• 2003

The photodynamics of excited-state intramolecular proton transfer reaction of 1-hydroxyanthraquinone (1-HAQ) and 1-deuterioanthraquinone was investigated in toluene with time-resolved emission and femtosecond transient transmittance techniques at room temperature. The temporal profiles of transient transmittance of 1-HAQ could be well described with multi-decaying time constants. The ultrafast time constant within ca. 260 fs reflects the dynamics of proton transfer. The decay component of 2 ps is assigned to an additional proton translocation process induced by the intramolecular vibrational relaxation, whereas the decay component of 18 ps is assigned to the vibrational cooling process, while the long component (200 ps) can be explained in terms of the relaxation from excited-state keto-tautomer to its ground state. Time-resolved anisotropy decay dynamics and isotope effects on the photodynamics reveals that the ESIPT from enol-tautomer to keto-one of 1-HAQ is barrierless reaction and coupled to a vibrational relaxation process.

• Bulletin of the Korean Chemical Society
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• 제27권7호
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• pp.1009-1014
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• 2006

Density functional theory calculations are applied to investigate the intramolecular proton transfer in the tautomers of thymine radical cation and its hydrated complexes with one water molecule. The optimized structures and energies for 6 tautomers and 6 transition states of thymine radical cation are calculated at the B3LYP/6-311++G(d,p) level. It is predicted that the order of relative stability for the keto and enol tautomers of thymine radical cation is the same with that of the neutral thymine tautomers, though the enol tautomers are more stabilized with respect to the di-keto form in the radical cation than in the neutral state. A new channel of proton transfer from >C5-$CH_{3}$ of thymine is found to open and have the lowest energy barrier of other proton transfer processes in thymine radical cation. The roles of hydration are also investigated with thymine-water 1 : 1 complex ions. The presence of water significantly lowers the barrier of the proton transfer, which clearly shows the assisting role of hydration even with one water molecule

• Macromolecular Research
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• 제16권5호
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• pp.385-395
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• 2008

Synthesis and properties of novel excited-state intramolecular proton transfer (ESIPT) materials, recently developed in our group, are described. Highly efficient ESIPT reaction, achieved in polyquinolines, polybenzoxazoles, and oxadiazole and imidazole derivatives possessing an intramolecular tautomerizable hydrogen bond, has been investigated theoretically and experimentally. It is demonstrated that unique properties arising from the ESIPT process (large Stokes' shift, no self-absorption, and easy population inversion, etc.) make it possible to produce advanced polymer devices for lasing, optical storage, and electroluminescence.

• 한국고분자학회:학술대회논문집
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• 한국고분자학회 2006년도 IUPAC International Symposium on Advanced Polymers for Emerging Technologies
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• pp.35-36
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• 2006

Excited-state intramolecular proton transfer (ESIPT) is a phototautomerization occurring in the excited states of the molecules possessing a cyclic intramolecular or solvent-bridged hydrogen bond. Recently, we have developed novel ESIPT chromophores, molecules, dendrimers and polymers which show very high fluorescence quantum efficiency combined with the characteristic features of optical switching, fluorescence patterining, lasing, and electroluminescence. Broad overview of these topics will be given in this talk.

• Bulletin of the Korean Chemical Society
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• 제28권12호
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• pp.2343-2353
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• 2007

We report the application of time-dependent density functional theory (TDDFT) to the calculation of potential energy profile relevant to the excited state intramolecular proton transfer (ESIPT) processes in title molecules. The TDDFT single point energy calculations along the reaction path have been performed using the CIS optimized structure in the excited state. In addition to the Stokes shifts, the transition energies including absorption, fluorescence, and 0-0 transition are estimated from the TDDFT potential energy profiles along the proton transfer coordinate. The excited state TDDFT potential energy profile of SA and 3ASA resulted in very flat function of the OH distance in the range ROH = 1.0-1.6 A, in contrast to the relatively deep single minimum function in the ground state. Furthermore, we obtained very shallow double minima in the excited state potential energy profile of SA and 3ASA in contrast to the single minimum observed in the previous work. The change of potential energy profile along the reaction path induced by the substitution of electron donating groups (-NH2 and -OCH3) at different sites has been investigated. Substitution at para position with respect to the phenolic OH group showed strong suppression of excited state proton dislocation compared with unsubstitued SA, while substitution at ortho position hardly affected the shape of the ESIPT curve. The TDDFT results are discussed in comparison with those of CASPT2 method.

• Bulletin of the Korean Chemical Society
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• 제13권2호
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• pp.140-145
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• 1992

The excited state intramolecular proton transfer and physical properties of 7-hydroxyquinoline are studied in various solutions and heterogeneous systems by measuring steady state and time-resolved fluorescence, reflection and NMR spectra. Proton transfer is observed only in protic solvents owing to its requirement of hydrogen-bonded solvent bridge for proton relay transfer. The activation energies of the proton transfer are 2.3 and 5.4 kJ/mol in $CH_3OH$ and in $CH_3OD$, respectively. Dimers of normal molecules are stable in microcrystalline powder form and undergo an extremely fast concerted double proton transfer upon absorption of a photon, consequently forming dimers of tautomer molecules. In the supercage of zeolite NaY, its tautomeric form is stable in the ground state and does not show any proton transfer.

• Bulletin of the Korean Chemical Society
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• 제26권11호
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• pp.1706-1710
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• 2005

The excited-state intramolecular proton transfer (ESIPT) fluorescence in the 2-(2'-hydroxyphenyl)benzoxazole (HBO) derivatives with different electron donor and acceptor substituents was studied by spectroscopic and theoretical methods. Changes in the electronic transition, energy levels, and orbital diagrams of HBO analogues were investigated by the semi-empirical molecular orbital calculation and were correlated with the experimental spectral position of ESIPT keto emission. It was found that the presence of substituents, regardless of their nature, resulted in the red-shifted absorption relative to HBO. However, the spectral change of the ESIPT fluorescence was differently affected by the nature of substituent: hypsochromic shift with electron donor and bathochromic shift with electron acceptor.