Double-proton-transfer reaction in the excited state of 1-azacarbazole dimer and 1-azacarbazole-7-azaindole heterodimer studied in a supersonic jet

Fuke, Kiyokazu; Yabe, T.; Chiba, Natsuyo; Kohida, Tomoyuki; Kaya, Kunimitsu

doi:10.1021/j100402a011

Cited by 34 publications

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“…The mechanism of ESDPT in 7AI 2 could be compared with that in the 1-azacarbazole dimer (1AC 2 ) studied by Fuke et al with electronic spectroscopy and picosecond time-resolved fluorescence spectroscopy in a supersonic free jet expansion. 77,78 The bandwidths in the FE spectrum of 1AC 2 are much narrower than those of 7AI 2 , suggesting that the ESDPT rate is much slower in 1AC 2 . 77 The decay profiles obtained by the excitation of the origin and intermolecular vibrations were fitted to single exponential functions.…”

Section: Mechanism Of Esdpt Revealed By Kiementioning

confidence: 99%

“…77,78 The bandwidths in the FE spectrum of 1AC 2 are much narrower than those of 7AI 2 , suggesting that the ESDPT rate is much slower in 1AC 2 . 77 The decay profiles obtained by the excitation of the origin and intermolecular vibrations were fitted to single exponential functions. 78 The time constants were determined to be 330, 130, and 355 ps for the excitation of the origin, 0 0 þ 109 and 0 0 þ 67 cm À1 vibrations, respectively, where the 0 0 þ 109 and 0 0 þ 67 cm À1 vibrations were assigned to the intermolecular stretching and intermolecular bending fundamentals.…”

Section: Mechanism Of Esdpt Revealed By Kiementioning

confidence: 99%

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Excited-State Double-Proton Transfer in the 7-Azaindole Dimer in the Gas Phase. Resolution of the Stepwise versus Concerted Mechanism Controversy and a New Paradigm

Sekiya¹,

Sakota²

2006

Bulletin of the Chemical Society of Japan

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The 7-azaindole dimer (7AI 2 ) is a prototype of double hydrogen-bonded molecules. 7AI 2 has been considered as a model DNA base pair and has attracted much attention to the mechanism of the excited-state double-proton transfer (ESDPT). Two ESDPT mechanisms, stepwise and concerted mechanisms, have been proposed so far. Great efforts have been devoted to clarify the mechanism of ESDPT using experimental and theoretical methods. However, the reaction mechanism had been controversial for more than a decade. We provide the resolution of the two mechanisms on the basis of new data obtained from electronic spectroscopy and picosecond time-resolved spectroscopy in the gas phase. The initial state of the ESDPT reaction has been well characterized by investigating the exciton resonance interaction with UV-UV hole-burning spectroscopy for various 7AI 2 isotopomers. The lowest-excited state of 7AI 2 has been classified into the weak coupling case of the exciton theory. We have concluded that the ESDPT reaction in 7AI 2 occurs via the concerted mechanism on the basis of the results of picosecond time-resolved experiments and the H/D kinetic isotope effect on ESDPT studied by measuring the vibronic-state selective dispersed fluorescence spectra. ESDPT of 7AI 2 has a ''dynamic cooperative'' nature that may arise from the coupling of the two moving protons with the reorganization of electrons. We have provided a new paradigm of ESDPT, where two quantum effects, the exciton resonance interaction and the proton tunneling, are concerned with the ESDPT reaction.Proton-transfer reactions are one of the most basic reactions, and they are important in physics, chemistry, and biology. [1][2][3][4][5][6] Spectroscopic studies on various proton-transfer systems combining with theoretical studies have provided rich information about the hydrogen-bonded structure and proton-transfer dynamics. In particular, a very detailed picture has been obtained for intramolecular single-proton transfer in polyatomic molecules, with laser spectroscopic measurements in the gas phase combining with theoretical studies. For example, a proton transfers by quantum mechanical tunneling mechanism when a potential energy barrier exists on a potential energy surface. The proton tunneling was clearly observed in the electronic and vibrational spectra of several polyatomic molecules. [6][7][8][9][10] Spectroscopic data and theoretical studies showed that the proton tunneling has a multi-dimensional nature, i.e., the motion of the moving proton couples with the coordinates of the heavy atoms that constitute the molecule. Such a multi-dimensional nature and quantum mechanical tunneling are important properties that characterize proton-transfer reactions. Now much effort is devoted to obtain a more complete picture for singleproton transfer reactions and also a new picture for more complicated multiproton-transfer reactions. There are many examples of multiproton-transfer reactions such as proton relay systems in enzymes, in hydrogen-bonded water complexes, and prot...

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Section: Mechanism Of Esdpt Revealed By Kiementioning

confidence: 99%

Section: Mechanism Of Esdpt Revealed By Kiementioning

confidence: 99%

Excited-State Double-Proton Transfer in the 7-Azaindole Dimer in the Gas Phase. Resolution of the Stepwise versus Concerted Mechanism Controversy and a New Paradigm

Sekiya¹,

Sakota²

2006

Bulletin of the Chemical Society of Japan

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“…To overcome these problems and to unveil the potential energy surfaces involved and the reaction dynamics progressed, the absorption and emission properties of (7-AI) 2 and (1-AC) 2 were examined in molecular beam since 1980's [15][16][17][18]. The dimers in supersonically cooled and isolated conditions allowed to get insight into the intrinsic nature of the excited-state PTR (ESPTR) such as the tunneling and vibrational mode specific reaction rates in addition to the information on the potential energy surfaces.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of proton transfer reactions of model base pairs in the ground and excited states: Revisited

Fuke

Ishikawa

2015

Chemical Physics Letters

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A review of the proton transfer reactions (PTR) of model base pairs such as the 7-azaindole and 1-azacarbazole dimers is presented, including some of the recent progress in the laser spectroscopy of these dimers. Advances in computational chemistry now allow to calculate reliable potential energy surfaces of the excited-state PTR, which is indispensable to understand the experimental results. The comprehensive results on the spectroscopy and reactivity of these dimers are outlined for fully explaining the excited state PTR of model base pairs on the basis of the current theoretical studies. Moreover, the recent studies on the PTR in the ground state relating to a back proton translocation of tautomeric dimer of 7-azaindole are presented. Finally, the outlook on the study of the PTR of model base pairs is addressed to further explore the reaction dynamics of these benchmark systems.

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“…α-carboline, or 1-azacarbazole, AC, Scheme 1, is another representative diaza-aromatic molecule that can experience an ESDPT process and phototautomerism. Because of its structural relation with 7AI, the photophysics of AC has received outstanding attention [10][11][12][13][14][15][16][17][18][19][20]. Thus, it has been reported that AC forms, similarly to 7AI, cyclic doubly hydrogen-bonded dimers and solute/solvent complexes in hydrocarbon and alcoholic solvents, respectively.…”

Section: Introductionmentioning

confidence: 99%

Spectral and Photophysical Properties of α-carboline (1-Azacarbazole) in Aqueous Solutions

et al. 2011

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The absorption and fluorescence spectra of α-carboline, 9H-pyrido[2,3-b]indole, AC, in organic aprotic solvents containing different water proportions and in acid/base aqueous solutions inside and outside the pH range have been examined. In the organic aprotic solvents, the addition of increasing concentrations of water sequentially quenches and shifts to the red the fluorescence spectra of AC. These spectral changes have been rationalized assuming the formation, at the lower water concentrations, of a discrete ground state non-cyclic weakly fluorescent AC hydrate emitting at 376 nm that, upon increasing the water concentrations, evolves to a higher order AC poly hydrate emitting at 397 nm. The changes of the AC absorption spectra in aqueous acid/basic solutions indicate the existence of three ground state prototropic species; the pyridinic protonated cation, C (pK(a) = 4.10 ± 0.05), the neutral, N (pK(a) = 14.5 ± 0.2), and the pyrrolic deprotonated anion, A. Conversely, the changes of the AC fluorescence spectra in these media indicate the existence of four excited state species emitting at 376 nm, 397 nm, 460 nm and 465 nm. Since the emissions at 376 nm and 397 nm satisfactorily match those of the hydrates observed in the organic-water mixtures, they were consistently assigned to two differently hydrated ground state N species. The remaining emissions at 460 nm and 465 nm have been assigned without ambiguity, on the basis of their excitation spectra, to the C and A species, respectively. The excited-state pK(a)s of the prototropic species of AC have been estimated by using the Förster-Weller cycle.

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Double-proton-transfer reaction in the excited state of 1-azacarbazole dimer and 1-azacarbazole-7-azaindole heterodimer studied in a supersonic jet

Cited by 34 publications

References 0 publications

Excited-State Double-Proton Transfer in the 7-Azaindole Dimer in the Gas Phase. Resolution of the Stepwise versus Concerted Mechanism Controversy and a New Paradigm

Excited-State Double-Proton Transfer in the 7-Azaindole Dimer in the Gas Phase. Resolution of the Stepwise versus Concerted Mechanism Controversy and a New Paradigm

Dynamics of proton transfer reactions of model base pairs in the ground and excited states: Revisited

Spectral and Photophysical Properties of α-carboline (1-Azacarbazole) in Aqueous Solutions

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