Issue 4, 2016

Contrasting ring-opening propensities in UV-excited α-pyrone and coumarin


The photoisomerisation dynamics following excitation to the S1 electronic state of two structurally related heterocyclic molecules, α-pyrone and coumarin, in acetonitrile solution have been probed by time-resolved vibrational absorption spectroscopy. Following irradiation at 310 nm, α-pyrone relaxes rapidly from its initially excited state, with a quantum yield for parent molecule reformation of 68%. Probing the antisymmetric ketene stretch region between 2100 cm−1 and 2150 cm−1 confirms the presence of at least two isomeric ring-opened photoproducts, which are formed highly vibrationally excited and relax on a picosecond timescale. Following vibrational cooling, a secondary, thermally driven, isomerisation is observed with a 1.8(1) ns time constant. In contrast, coumarin reforms the parent molecule with essentially 100% efficiency following excitation at 330 nm. The conical intersections driving the non-radiative relaxation of α-pyrone have been investigated using an automated search algorithm. The two lowest energy conical intersections possess remarkably similar structures to the two energetically accessible conical intersections reported previously for coumarin, suggesting that the differing photochemistry is the result of dynamical effects occurring after passage through these intersections.

Graphical abstract: Contrasting ring-opening propensities in UV-excited α-pyrone and coumarin

Supplementary files

Article information

Article type
29 Oct 2015
16 Dec 2015
First published
16 Dec 2015
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2016,18, 2629-2638

Contrasting ring-opening propensities in UV-excited α-pyrone and coumarin

D. Murdock, R. A. Ingle, I. V. Sazanovich, I. P. Clark, Y. Harabuchi, T. Taketsugu, S. Maeda, A. J. Orr-Ewing and M. N. R. Ashfold, Phys. Chem. Chem. Phys., 2016, 18, 2629 DOI: 10.1039/C5CP06597F

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

Read more about how to correctly acknowledge RSC content.

Social activity