Excited-state barrier controls E → Z photoisomerization in p-hydroxycinnamate biochromophores

Ashworth, Eleanor K., Coughlan, Neville J. A., Hopkins, W. Scott, Bieske, Evan J. and Bull, James N. ORCID: https://orcid.org/0000-0003-0953-1716 (2022) Excited-state barrier controls E → Z photoisomerization in p-hydroxycinnamate biochromophores. The Journal of Physical Chemistry Letters, 13 (39). pp. 9028-9034. ISSN 1948-7185

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Molecules based on the deprotonated p-hydroxycinnamate moiety are widespread in nature, including serving as UV filters in the leaves of plants and as the biochromophore in photoactive yellow protein. The photophysical behavior of these chromophores is centered around a rapid E → Z photoisomerization by passage through a conical intersection seam. Here, we use photoisomerization and photodissociation action spectroscopies with deprotonated 4-hydroxybenzal acetone (pCK–) to characterize a wavelength-dependent bifurcation between electron autodetachment (spontaneous ejection of an electron from the S1 state because it is situated in the detachment continuum) and E → Z photoisomerization. While autodetachment occurs across the entire S1(ππ*) band (370–480 nm), E → Z photoisomerization occurs only over a blue portion of the band (370–430 nm). No E → Z photoisomerization is observed when the ketone functional group in pCK– is replaced with an ester or carboxylic acid. The wavelength-dependent bifurcation is consistent with potential energy surface calculations showing that a barrier separates the Franck–Condon region from the E → Z isomerizing conical intersection. The barrier height, which is substantially higher in the gas phase than in solution, depends on the functional group and governs whether E → Z photoisomerization occurs more rapidly than autodetachment.

Item Type: Article
Additional Information: Acknowledgements: This research was funded through a University of East Anglia start-up allowance (to J.N.B.), the Australian Research Council Discovery Project scheme (DP150101427 and DP160100474 to E.J.B.), and a NSERC Discovery Grant (RGPIN-2017-04217 to W.H.S.). E.K.A. acknowledges a University of East Anglia doctoral studentship. N.J.A.C. acknowledges a Vanier-Banting Postdoctoral Fellowship from NSERC. Dr. Palas Roy is thanked for training on the fluorescence upconversion experiment. Electronic structure calculations were performed on the High Performance Computing Cluster supported by the Research and Specialist Computing Support service at the University of East Anglia.
Faculty \ School: Faculty of Science > School of Chemistry
UEA Research Groups: Faculty of Science > Research Groups > Centre for Photonics and Quantum Science
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Depositing User: LivePure Connector
Date Deposited: 26 Sep 2022 09:31
Last Modified: 09 Feb 2023 13:51
URI: https://ueaeprints.uea.ac.uk/id/eprint/88629
DOI: 10.1021/acs.jpclett.2c02613


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