Direct optical studies of proton tunneling in hydrogen bonded mixed molecular crystals

doi:10.1016/0022-2313(84)90048-6

Journal of Luminescence

Volumes 31–32, Part 2, December 1984, Pages 517-524

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Abstract

Absorption and fluorescence spectra of dye molecules doped substitutionally into benzoic acid crystals provide very sensitive probes of the environment. Processes related to a rearrangement of the acid protons can be probed directly at very low temperatures.

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Cited by (8)

Proton tunnelling reactions in pentacene doped benzoic acid crystals
1995, Chemical Physics
Optical excitation of pentacene, doped into a benzoic acid crystal matrix, induces a reversible proton transfer reaction between the host and the guest. This reaction occurs at low temperatures and leads to the creation of defects corresponding to the displacement, from its regular position, of an acid proton of the host matrix. The formation and evolution of these defects is monitored via the electronic S₀ → S₁ transition of the pentacene guest. Here we report and discuss a variety of measurements made with the aim of obtaining information about the first step of the reaction. It is shown that the rate for the first step of this reaction is reduced by a factor of about 10⁴ upon deuteration of the host matrix, demonstrating that this step occurs by tunnelling. Other unsuccessful experiments (optical, ESR, magnetic field effects) made to identify the first intermediate of the reaction as well as molecular orbital calculations of potential intermediates are also reported briefly. It is shown that the formation of the pentacene cation, protonated in the centre position, is consistent with all observations. This species is proposed as the most likely first intermediate of the reaction.
Pathways of spontaneous and photoinduced hydrogen tunnelling in organic crystals
1994, Journal of Photochemistry and Photobiology, A: Chemistry
Optical excitation at liquid helium temperature of pentacene molecules embedded in benzoic acid crystals gives rise to defects in the environment of pentacene. By deuteration of the acid proton of the matrix and/or selective deuteration of the pentacene molecules, it has been proven that these defects are due to the displacement of acid protons of the matrix and are produced by reversible proton transfer between the benzoic acid host and the pentacene guest. The defect sites are unstable and decay with lifetimes ranging from subseconds to hours. Different defect sites also interconvert spontaneously in the dark or after absorption of a second photon.
Deuteration effect on photoinduced hydrogen motions in low temperature mixed molecular crystals
1992, Journal of Luminescence
Irradiation at liquid helium temperatures of benzoic acid crystals doped with pentacene leads to a reversible bleaching of the pentacene absorption and the appearance of defect sites related to a rearrangement of the acid protons of the host. Upon deuteration of these acid protons a partial H/D exchange in pentacene during the crystal growth is observed. Different partially deuterated pentacene molecules give rise to distinct 0-0 bands. Selective and non-selective laser irradiations show that the yield of the reaction leading to the appearance of the defect sites varies strongly as a function of this partial deuteration of the guest pentacene molecule.
Localized and delocalized proton levels in hydrogen bonds: Fluorescence line narrowing and stark effect measurements
1987, Journal of Luminescence
Observation of delocalized states of the proton in carboxylic acid dimers in condensed matter
1987, Chemical Physics
We report fluorescence line-narrowing experiments on low-temperature molecular crystals composed of hydrogen bonded dimers of benzoic acid. The results indicate that the acid protons are distinctly delocalized in nearly symmetric double-well potentials. The tunneling frequency is 4.8 × 10⁹ s⁻¹, a quantity not previously measured for acid protons. This is the first observation of delocalized protons of acid dimers in the condensed phase.
Impurity-induced double proton transfer in benzoic acid crystals
1986, Chemical Physics Letters

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^☆: This research was supported by a grant (to RMH) from the Division of Materials Research of the National Science Foundation DMR-8116629, and in part by the NSF-CNRS US-France Program (NSF INT-8213024).

⁺: Present address: Department of Chemistry, University of Rochester, Rochester, NY 14627.

^#: Present address: Department 902 APIA Abbott Labortories, Abbott Park, IL 60061.

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Direct optical studies of proton tunneling in hydrogen bonded mixed molecular crystals☆

Abstract

Chem. Phys. Letters

J. Chem. Phys.

J. Chem. Phys.

J. Chem. Phys.

Chem. Phys. Letters

Acta Cryst.

Acta Cryst.

Chem. Phys. Letters

J. Chem. Phys.

J. Chem. Phys.