UV-Induced Isomerization Dynamics of N-Methyl-2-pyridone in Solution

Daniel Murdock, Stephanie J Harris, Ian P Clark, Gregory M Greetham, Michael Towrie, Andrew J Orr-Ewing, Michael N R Ashfold

Research output: Contribution to journalArticle (Academic Journal)

8 Citations (Scopus)
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Abstract

The photoisomerization dynamics of N-methyl-2-pyridone (NMP) dissolved in CH3CN have been interrogated by time-resolved electronic and vibrational absorption spectroscopy. Irradiation at two different wavelengths (330 or 267 nm) prepares NMP(S1) molecules with very different levels of vibrational excitation, which rapidly relax to low vibrational levels of the S1 state. Internal conversion with an associated time constant of 110(4) ps, leading to reformation of NMP(S0) molecules, is identified as the dominant (>90%) decay pathway. Much of the remaining fraction undergoes a photoinitiated rearrangement to yield two ketenes (revealed by their characteristic antisymmetric C═C═O stretching modes at 2110 and 2120 cm(-1)), which are in equilibrium. The rate of ketene formation is found to be pump-wavelength dependent, consistent with ab initio electronic structure calculations which predict a barrier on the S1 potential energy surface en route to a prefulvenic conical intersection, by which isomerization is deduced to occur. Two kinetic models-differentiated by whether product branching occurs in the S1 or S0 electronic states-are presented and used with equal success in the analysis of the experimental data, highlighting the difficulties associated with deducing unambiguous mechanistic information from kinetic data alone.

Original languageEnglish
Pages (from-to)88-94
Number of pages7
JournalJournal of Physical Chemistry A
Volume119
Issue number1
Early online date3 Dec 2014
DOIs
Publication statusPublished - 8 Jan 2015

Bibliographical note

Accepted 03/12/2014

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