Bridging the Gap between the Gas Phase and Solution Phase: Solvent Specific Photochemistry in 4-tert-Butylcatechol

Abstract

(2015) Bridging the gap between the gas and solution phase : solvent specific photochemistry in 4-tert-butylcatechol. Journal of Physical Chemistry A, 119 (50). pp. 11989-11996. Permanent WRAP URL:http://wrap.warwick.ac.uk/83205 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-for profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher's statement:This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry A, copyright © American Chemical Society after peer review and technical editing by the publisher.To access the final edited and published work see http://dx.doi.org/10.1021/acs.jpca.5b03621 A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP url' above for details on accessing the published version and note that access may require a subscription. ABSTRACT: Eumelanin is a naturally synthesized ultraviolet light absorbing biomolecule, possessing both photoprotective and phototoxic properties. We infer insight into these properties of eumelanin using a bottom-up approach, by investigating a subunit analogue, 4-tert-butylcatechol. Utilizing a combination of femtosecond transient electronic absorption spectroscopy and time-resolved velocity map ion imaging, our results suggest an environmental-dependent relaxation pathway, following irradiation at 267 nm to populate the S1 ( 1 ππ*) state. Gas-phase and non-polar solution-phase measurements reveal that the S1 state decays through coupling onto the S2 ( 1 πσ*) state that is dissociative along the non-intramolecular hydrogen bonded 'free' O-H bond. This process is mediated by tunneling beneath an S1/S2 conical intersection and occurs in 4.9 ± 0.6 ps in the gas-phase and 27 ± 7 ps in the non-polar cyclohexane solution. Comparative studies on the deuterated isotopologue of 4-tert-butylcatechol in both the gas-and solution-phase (cyclohexane) reveals an average kinetic isotope effect of ~19 and ~7, respectively, supportive of O-H dissociation mediated by a quantum tunneling mechanism. In contrast, in the polar acetonitrile, the S1 state decays on a much longer timescale of 1.7 ± 0.1 ns. We propose that the S1 decay is now multicomponent, likely driven by internal c...

Broadband ultrafast photoprotection by oxybenzone across the UVB and UVC spectral regions

“…8 Furthermore, for all excitation wavelengths, we note that the GSB has not fully recovered, seen from the non-zero baseline out to the maximum delay time of our experiment (1.7 ns), see Fig. Further support for this conclusion is provided by previous studies of HBT 34 and 4-tert-Butylcatechol 35 for example. We can begin to rationalise these features drawing on ab initio calculations performed in previous studies.…”

Intermolecular Hydrogen Bonding Modulates O‐H Photodissociation in Molecular Aggregates of a Catechol Derivative

“…The signals for the 5 m m solution agree very well with ones reported by Horbury et al . , while signals of 4‐tBuC aggregates are reported here for the first time.…”

“…The UV absorption spectrum of a 6 m m solution of 4‐tBuC in cyclohexane exhibits pronounced vibronic structure (Fig. a), reminiscent of that of 4‐tBuC in the gas‐phase . As the concentration is increased above ~20 m m , the spectrum loses vibronic structure and blue shifts slightly.…”

“…In agreement with Horbury et al . , the primary photochemical reaction of 4‐tBuC in a weakly interacting, nonpolar solvent is homolytic O‐H bond dissociation, resulting in hydrogen atom ejection to the solvent and formation of a neutral semiquinone radical. In contrast, intermolecular hydrogen bonding in 4‐tBuC aggregates fosters excited state structural relaxation and slows the O‐H bond dissociation that ultimately gives rise to hydrogen‐bonded neutral semiquinone radicals.…”

Photodynamics of potent antioxidants: ferulic and caffeic acids

“…Additionally, this work also highlighted a potential dissociation of the hydrogen atom on the phenolic hydroxyl group via tunnelling; this mechanism has been previously seen experimentally in the building blocks of ferulic and caffeic acids, notably guaiacol and catechol respectively. 34,35 In light of these works, and the apparent need for a better understanding of the photodynamics of ferulic acid and caffeic acid as sunscreening agents, we use femtosecond (fs) TEAS to revisit the photodynamics of ferulic acid and provide new insight toward the hitherto unstudied caffeic acid, following photoexcitation to the 1 1 pp* state, in a range of solvent environments of varying polarity.…”