Photo‐Induced and Spontaneous Proton Tunneling in Molecular Solids

Trommsdorff, H.P.

doi:10.1002/9780470133552.ch3

Cited by 9 publications

(6 citation statements)

References 191 publications

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“…In a simple 1D model, the residence time of a particle oscillating between two wells is given by h/Δ, where Δ is the tunneling splitting. 69 Using the ground state value of 4.4 cm −1 , observed for the 0−0 transition, leads to 7.1 ps, the same order of magnitude as the value determined in a condensed phase. Even closer is the value of 2.6 ps obtained from the value of tunneling splitting in porphycene vibrationally excited by one quantum of 2A g 180 cm −1 vibration (12 cm −1 ).…”

Section: Resultssupporting

confidence: 59%

“…The tunneling splitting observed for 1 ,, provides the rate of coherent double hydrogen tunneling in an isolated molecule. In a simple 1D model, the residence time of a particle oscillating between two wells is given by h /Δ, where Δ is the tunneling splitting . Using the ground state value of 4.4 cm –1 , observed for the 0–0 transition, leads to 7.1 ps, the same order of magnitude as the value determined in a condensed phase.…”

Section: Results and Discussionmentioning

confidence: 76%

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Tautomerism in Porphycenes: Analysis of Rate-Affecting Factors

et al. 2014

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Double hydrogen transfer occurring in both ground and the lowest electronically excited singlet states was studied for a series of 19 differently substituted porphycenes. The rates of tautomerization have been determined using femtosecond pump-probe spectroscopy with polarized light. The values vary by over 3 orders of magnitude, suggesting the importance of tunneling. Good correlation exists between the values of the rates and the parameters characterizing the strength of two intramolecular hydrogen bonds: proton NMR shift, distance between the hydrogen-bonded nitrogen atoms, and the NH stretching frequency. While hydrogen-bond strength is the main factor determining the rate of double hydrogen transfer, other factors, such as static and dynamic symmetry breaking and the population of low-frequency vibrations also have to be taken into account.

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Section: Resultssupporting

confidence: 59%

Section: Results and Discussionmentioning

confidence: 76%

Tautomerism in Porphycenes: Analysis of Rate-Affecting Factors

et al. 2014

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“…29 In the incoherent tunneling regime the rate is proportional to Δ 2 , the square of the tunneling splitting. 1,52 We obtain (12/4.4) 2 = 7.4, in excellent agreement with k 1 /k 0 = 7.0 ± 0.9.…”

supporting

confidence: 78%

“…A ccepted to occur under nonroutine conditions, i.e., in isolated molecules at low temperatures, 1 hydrogen tunneling in room-temperature, condensed phase reactions continues to be a subject of intense research. 2 The ubiquitousness as well as chemical and biological importance of hydrogen transfer lead scientists to seek tunneling contributions in such processes as spontaneous DNA damage 3,4 or various enzymecatalyzed reactions.…”

mentioning

confidence: 99%

“…Accepted to occur under nonroutine conditions, i.e., in isolated molecules at low temperatures, hydrogen tunneling in room-temperature, condensed phase reactions continues to be a subject of intense research . The ubiquitousness as well as chemical and biological importance of hydrogen transfer lead scientists to seek tunneling contributions in such processes as spontaneous DNA damage , or various enzyme-catalyzed reactions. − Most of the experiments, especially in enzymes, infer tunneling exclusively by measuring isotope effects on product formation. − Attempting to elucidate inherently fast phenomena by observing slow processes, such experiments require an additional assumption on hydrogen transfer being the rate-limiting step in a series of reactions.…”

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confidence: 99%

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Evidence for Dominant Role of Tunneling in Condensed Phases and at High Temperatures: Double Hydrogen Transfer in Porphycenes

Ciąćka

Fita

Listkowski

et al. 2016

J. Phys. Chem. Lett.

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Investigation of the double hydrogen transfer in porphycene, its 2,7,12,17-tetra-tert-butyl derivative, and their N-deuterated isotopologues revealed the dominant role of tunneling, even at room temperature in condensed phase. Ultrafast optical spectroscopy with polarized light employed in a wide range of temperatures allowed the identification and evaluation of contributions of two tunneling modes: vibrational ground-state tunneling, occurring from the zero vibrational level, and vibrationally activated, via a large amplitude, low-frequency mode. Good correspondence was found between the rates of incoherent tunneling occurring in condensed phase and the values estimated on the basis of tunneling splittings observed in molecules isolated in supersonic jets or helium nanodroplets. The results provide solid experimental insight into widely proposed quantum facets of ubiquitous hydrogen-transfer phenomena.

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Tautomerization in Porphycenes

Waluk

2006

Hydrogen‐Transfer Reactions

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Porphyrins and metalloporphyrins are objects of intense studies in both basic and applied sciences. Owing to their crucial role in biological processes, such as photosynthesis, oxygen transport and activation, porphyrins have been labeled "Pigments of Life" [1]. The accuracy of this characterization is additionally confirmed by the use of porphyrins in medicine as phototherapeutic agents [2][3][4][5][6]. The potential of porphyrins as building blocks is enormous and includes, for example, artificial light-harvesting and photosynthetic systems [7-9], molecular memories [10,11], photovoltaic devices [12], and many other advanced materials [13][14][15][16][17][18]. The prospect of applications stimulated a rapid development of synthetic procedures that resulted in obtaining new classes of compounds, such as expanded, contracted, or inverted porphyrins [19,20]. Of particular interest in this area are constitutional isomers of porphyrin (also dubbed "reshuffled" porphyrins) [20], tetrapyrrole macrocycles which differ from the parent molecule in the way of linking the pyrrole rings by methine groups (Fig. 8.1). The research in this field started with the synthesis of porphycene in 1986 [21]. Since then, three more "nitrogen-in" isomers have been obtained: corrphycene [22], hemiporphycene [23,24], and isoporphycene [25,26]. Closely related to this class is an "inverted" ("N-confused") porphyrin [27,28].All these molecules have been shown to be planar and aromatic. They also exhibit electronic spectra characteristic for porphyrins, with the lower intensity Q transitions in the red part of the visible region followed by stronger Soret bands in the near-UV (Fig. 8.2). However, the relative intensities of the Q and Soret transitions differ significantly among the series. The lowest intensity of Q bands is observed in porphyrin and corrphycene. Hemiporphycene reveals stronger Q bands, and porphycene even stronger ones. This behavior can be rationalized upon inspecting the energies of the frontier p orbitals. The analysis of HOMO and LUMO splitting based on the perimeter model [29] has led to correct predictions not only for relative absorption intensities, but also for signs and patterns in magnetic circular dichroism. These predictions were experimentally confirmed for porphycene [30], corrphycene [31], and hemiporphycene [32].Hydrogen-Transfer Reactions. Edited by

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Photo‐Induced and Spontaneous Proton Tunneling in Molecular Solids

Cited by 9 publications

References 191 publications

Tautomerism in Porphycenes: Analysis of Rate-Affecting Factors

Tautomerism in Porphycenes: Analysis of Rate-Affecting Factors

Evidence for Dominant Role of Tunneling in Condensed Phases and at High Temperatures: Double Hydrogen Transfer in Porphycenes

Tautomerization in Porphycenes

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