Theoretical studies on the spectroscopy of the 7‐azaindole monomer and dimer

Serrano‐Andrés, Luis; Merchán, Manuela; Borin, Antonio Carlos; Stålring, Jonna

doi:10.1002/qua.1320

Cited by 33 publications

(37 citation statements)

References 39 publications

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“…The CASPT2 method was not executed on the 7AI dimers because of the enormous computational cost involved. A first attempt to execute the CASPT2 method on the classic C 2h 7AI dimer has been recently reported (15) with frozen 1s core electrons, and very limited number of atomic functions on the C, N, and H atoms, by including excited-state geometry optimization at the CASSCF level, to reproduce experimental vertical electronic transitions of the monomer and dimer molecule. (iv) Time-dependent DFT calculations, which also include dynamical electron correlation (unpublished work), have been used for calculating the PT potential energy curve of the first electronic excited state of the classic C 2h 7AI dimer to the double-proton transfer tautomer.…”

Section: Theoretical Methodsmentioning

confidence: 99%

The concerted mechanism of photo-induced biprotonic transfer in 7-azaindole dimers: A model for the secondary evolution of the classic C _2h dimer and comparison of four mechanisms

Catalán

Pérez

Valle

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

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A mechanism is proposed for the formation in gas phase, during a short time, of the delicately symmetrical coplanar C 2h classic 7-azaindole (7AI) doubly hydrogen-bonded dimer. Of the five card-pack or otherwise random geometry structures most likely to be formed in the supersonic jet expansion molecular beam, none would be an obvious precursor to the C 2h dimer. One unstable dimer with dipole-dipole, van der Waals, and plane-to-plane hydrogen bonding is shown to be capable of unhinging about the hydrogen-bond pair as an axis, from 0°to 90°to 180°, yielding a deep minimum for the C 2h structure with its delicate geometry and symmetry. This relaxation mechanism is feasible in the 3-s interval between the nozzle escape and the first laser pulse interception of the molecular beam. In the second part of the paper four published mechanisms are compared for concerted vs. two-step biprotonic phototransfer for the 7AI dimers. The dependence of the latter two models on H-atom instead of proton-transfer as an intermediate step negates the mechanism in a singlet (,*) electronic state by the valency repulsion, in the 3-electron orbital that would be generated. The concerted mechanism for biprotonic phototransfer is reaffirmed by the analysis of the quantum mechanical conditions set on the biprotonic transfer in the photo-excited molecular 7AI pair. M olecular pairs in valency, H-bonding, or close van der Waals interaction upon excitation are subject to in-phase perturbation by the photon electromagnetic field, in most cases the electric-dipole component. The resultant excitation is perforce coherent. In a doubly H-bonded pair such as the classic C 2h dimer of 7-azaindole (7AI), the coherent excitation induces several simultaneity responses. The molecular pair exhibits (i) excitonic state splitting, (ii) a shift of electron density within the framework of each molecule, resulting in synchronous acid-base changes at opposite ends of the molecule, and (iii) intermolecular acceptance vs. ejection with respective coordinated ejection vs. acceptance of protons in the partner molecule. These simultaneity principles were presented in the companion paper (1). In the research on (7AI) 2 photo-induced biprotonic transfer, the final molecular (7AI) product appears as the classic C 2h 7AI tautomer pair. This is a structure of snowflake-like symmetric delicacy. It is coplanar, centrosymmetric, and is in the C 2h symmetry point group, the most symmetric of the set of dimers studied. Upon adiabatic expansion by means of a supersonic nozzle with carrier gas, cooling the warm reservoir vapor to 7 K or less, dimerization can occur. In the preceding paper (1) we have shown calculations of six stable dimers with significant binding energies; five of them are either card-pack structures or rather random geometry dimers easily formable upon supersonic expansion.Although the calculations show the C 2h dimer to be the most stable of the six dimer structures considered, it seems most unlikely that the spatial orientation requirements of this rather ...

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Section: Theoretical Methodsmentioning

confidence: 99%

The concerted mechanism of photo-induced biprotonic transfer in 7-azaindole dimers: A model for the secondary evolution of the classic C _2h dimer and comparison of four mechanisms

Catalán

Pérez

Valle

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

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“…25 As demonstrated in the presentation of the method and in applications performed subsequently, the MS-CASPT2 level is able to handle spurious valence-Rydberg mixings. [25][26][27][28][29] The geometry of the relevant excited states has been optimized at the CASPT2 level. In total six excited states have been considered.…”

Section: Introductionmentioning

confidence: 99%

Theoretical characterization of the lowest-energy absorption band of pyrrole

Roos

Malmqvist

Molina

et al. 2002

The Journal of Chemical Physics

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121

145

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The lowest-energy band of the electronic spectrum of pyrrole has been studied with vibrational resolution by using multiconfigurational second-order perturbation theory ͑CASPT2͒ and its multistate extension ͑MS-CASPT2͒ in conjunction with large atomic natural orbital-type basis sets including Rydberg functions. The obtained results provide a consistent picture of the recorded spectrum in the energy region 5.5-6.5 eV and confirm that the bulk of the intensity of the band arises from a * intravalence transition, in contradiction to recent theoretical claims. Computed band origins for the 3s,3p Rydberg electronic transitions are in agreement with the available experimental data, although new assignments are suggested. As illustrated in the paper, the proper treatment of the valence-Rydberg mixing is particularly challenging for ab initio methodologies and can be seen as the main source of deviation among the recent theoretical results as regards the position of the low-lying valence excited states of pyrrole.

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“…Theoretical studies have been also carried out to investigate the hydrogen-bonded structures, potential energy curves (or surface), and molecular dynamics of 7AI 2 . [48][49][50][51][52][53][54][55][56][57][58] Nevertheless, the ESDPT dynamics of 7AI 2 has not been fully understood. Very recently, we extensively studied the ESDPT reaction in 7AI 2 in the gas phase with frequency resolved and time-resolved spectroscopy.…”

mentioning

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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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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Theoretical studies on the spectroscopy of the 7‐azaindole monomer and dimer

Cited by 33 publications

References 39 publications

The concerted mechanism of photo-induced biprotonic transfer in 7-azaindole dimers: A model for the secondary evolution of the classic C _2h dimer and comparison of four mechanisms

The concerted mechanism of photo-induced biprotonic transfer in 7-azaindole dimers: A model for the secondary evolution of the classic C _2h dimer and comparison of four mechanisms

Theoretical characterization of the lowest-energy absorption band of pyrrole

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

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Theoretical studies on the spectroscopy of the 7‐azaindole monomer and dimer

Cited by 33 publications

References 39 publications

The concerted mechanism of photo-induced biprotonic transfer in 7-azaindole dimers: A model for the secondary evolution of the classic C 2h dimer and comparison of four mechanisms

The concerted mechanism of photo-induced biprotonic transfer in 7-azaindole dimers: A model for the secondary evolution of the classic C 2h dimer and comparison of four mechanisms

Theoretical characterization of the lowest-energy absorption band of pyrrole

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

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The concerted mechanism of photo-induced biprotonic transfer in 7-azaindole dimers: A model for the secondary evolution of the classic C _2h dimer and comparison of four mechanisms

The concerted mechanism of photo-induced biprotonic transfer in 7-azaindole dimers: A model for the secondary evolution of the classic C _2h dimer and comparison of four mechanisms