• Bulletin of the Korean Chemical Society
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• 제30권7호
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• pp.1481-1484
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• 2009

When isolated phenol or a small phenol-solvent cluster is excited to the $S_1\;state\;of\;{\pi}{\pi}^*$ character, the hydrogen atom of the hydroxyl group dissociates via a ${\pi}{\sigma}^*$ state that is repulsive along the O-H bond. We computationally investigated the substitution effects of an amino group on the excited state hydrogen transfer reaction of phenol. The time-dependent density functional theory (TDDFT) with B3LYP functional was employed to calculate the potential energy profiles of the ${\pi}{\pi}^*$ and the ${\pi}{\sigma}^*$ excited states along the O-H coordinate, together with the orbital shape at each point, as the position of the substituent was varied. It was found that the amino substitution has an effect of lowering the ${\pi}{\sigma}^*$ state and enhancing the excited state hydrogen transfer reaction.

• Bulletin of the Korean Chemical Society
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• 제31권2호
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• pp.365-371
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• 2010

The multiconfiguration molecular mechanics (MCMM) algorithm was used to generate potential and vibrationally adiabatic energy surfaces for excited-state tautomerization in the 1:1 7-azaindole:$H_2O$ complex. Electronic structures and energies for reactant, product, transition state were computed at the CIS/6-31G(d,p) level of theory. The potential and vibrationally adiabatic energies along the reaction coordinate were generated step by step by using 16 high-level Shepard points, which were computed at the CIS/6-31G(d,p) level. This study shows that the MCMM method was applied successfully to make quite reasonable potential and adiabatic energy curves for the excited-state double proton transfer reaction. No stable intermediates are present in the potential energy curve along the reaction coordinate of the excited-state double proton transfer in the 1:1 7-azaindole:$H_2O$ complex, indicating that these two protons are transferred concertedly. The change in the bond distances along the reaction coordinate shows that two protons move very asynchronously to make an $H_3O^+$-like moiety at the transition state.

• 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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• 제34권2호
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• pp.465-469
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• 2013

Proton transfer reaction is one of the most fundamental processes in chemistry and life science. Excited state intramolecular proton transfer (ESIPT) has been studied as a model system of the proton transfer, since it can be conveniently initiated by light. We report ESIPT reaction dynamic of 1-hydroxy-anthraquione (1-HAQ) in solution by highly time-resolved fluorescence. ESIPT time of 1-HAQ is determined to be $45{\pm}10$ fs directly from decay of the reactant fluorescence and rise of the product fluorescence. High time resolution allows observation of the coherent vibrational wave packet motion in the excited state of the reaction product tautomer. The coherently excited vibrational mode involves large displacement of the atoms, which shortens the distance between the proton donor and the acceptor. With the theoretical analysis, we propose that the ESIPT of 1-HAQ proceeds barrierlessly with assistance of the skeletal vibration, which in turn becomes excited coherently by the ESIPT reaction.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.1015-1019
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• 2012

The direct calculation method is generalized to the excited-state diffusion-influenced reversible reaction of a neutral and a charged particle under an external field with two different lifetimes and quenching in three dimensions. The present method provides an alternative way to calculate the binding probability density functions and the survival probabilities from the corresponding irreversible results. The solutions are obtained as the series solutions by the diagonal approximation due to the anisotropy of the unidirectional external field. The numerical results are found to be in good agreement with those of the previous study [S. Y. Reigh et al. J. Chem. Phys. 132, 164112 (2010)] within a weak field limit. The solutions of two approaches show qualitatively the same overall behavior including the power laws at long times.

• Bulletin of the Korean Chemical Society
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• 제27권2호
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• pp.197-202
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• 2006

In the reaction A + B $^\rightarrow_\leftarrow$ C, where A and B are ionic reactants having opposite charges, a B molecule approaching an A will experience a switching of the interaction potential when the A molecule is captured by one of the other B molecules in the medium. In the reversible case, the former B molecule still has a chance to react with the A, so that one needs to take into account the switched interaction between the reactant B and the product C as well as that between the reactants to treat the kinetics accurately. It is shown that this kind of interaction potential switching affects the relaxation kinetics in an intriguing way as observed in a recent experiment on an excited-state proton transfer reaction.

• 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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• 제10권6호
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• pp.543-546
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• 1989

The photocycloaddition reaction of khellin with several olefins has been investigated. The photocycloadducts are formed regioselectively on furanyl 4',5'-double bond of khellin probably due to the localization of excitation energy on the furanyl 4',5'-double bond in the reactive excited state. The photocycloaddition reaction proceeds through the excited triplet state and the same product was formed when khellin is irradiated with dimethylfumarate or dimethylmaleate indicating the formation of common intermediate. The quantum yields of photocycloadduct formation, fluorescence, and intersystem crossing are very sensitive to proton-donating ability of solvents.

• Bulletin of the Korean Chemical Society
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• 제1권1호
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• pp.35-39
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• 1980

A vacuum ultraviolet photolysis of ethyl bromide was studied in the pressure range of 0.5-19.9 torr and at 123.6 nm krypton resonance line. The pressure effect on the reaction was studied by increasing the reactant pressure and by adding an inert gas, e.g., He. In the observation the monatomic gas is found to be no effect in the reaction. A scavenger effect of the reaction was also performed by adding NO gas as a radical scavenger and was found to be quite efficient to scavenge a radical product $C_2H_6$. The observation of the major reaction product $C_2H_6$ was interpreted in terms of a molecular elimination. Nontheless the decreasing phenomenon of ${\phi}_{C_2H_4}/{\phi}_{C_2H_6}$ with pressure rise was attributed to the existence of the two electronically excited states. One state proceeds to the molecular elimination and the other to carbon-bromine bond fission. The excitation and the decomposition mechanisms between two excited states and the reaction products were interpreted in terms of the first excitation which proceeds the molecular elimination, and the second excitation which resulted from the first excited state by collisional cross over decomposes by carbon-bromine bond fission.

• Bulletin of the Korean Chemical Society
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• 제34권7호
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• pp.1961-1966
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• 2013

Theoretical investigations have been performed for the ground state ($S_0$) and the first excited state ($S_1$) of the hydrogen bonded green fluorescent protein (GFP) model. The potential energy surface (PESs) of $S_0$ was obtained by B3LYP method and that of $S_1$ was obtained by CIS method. Based on the relative stabilities of species and the energy barriers for the proton transfer, it was found that proton transfer could take place both under the ground state and the first excited state. As determined by the proton motions along the reaction coordinate, both the ground state proton transfer (GSPT) and the excited state proton transfer (ESPT) are considered as a concerted and asynchronous process.