The gas-phase ultrafast photodynamics of ethyl sinapate and diethyl sinapate Jack Dalton 1 and Vasilios Stavros 2 1 Department of Chemistry, University of Warwick, Coventry, UK, 2 School of Chemistry, University of Birmingham, Birmingham, UK Ethyl sinapate (ES) and its symmetrical derivative, diethyl sinapate (DES), belong to the sinapate family of molecules; a family known for strong ultraviolet absorption and efficient relaxation to the ground electronic state from excited electronic states. In solution, ES demonstrates remarkably quick relaxation from an initially populated S 1 (ππ*) state though a trans-cis isomerisation pathway towards a conical intersection with the electronic ground state. 1 For DES in solution, a similar mechanism occurs but with a nearly 10-fold reduction in the ‘isomerisation’ lifetime. 2 In contrast, little is known about how this symmetrisation of the ester moieties around the acrylic double bond affects the relaxation dynamics for sinapates in the gas-phase, thus on a fundamental level. Therefore, in this study, gas-phase femtosecond time-resolved ion-yield and photoelectron spectroscopies were used to map the subsequent photodynamics of ES and DES following photoexcitation to the S 1 (ππ*) state in the gas-phase. ES is found to relax from its initially populated S 1 (ππ*) state with lifetimes of ∼4.5 ps, ∼70 ps and a final lifetime that extends beyond our 1 ns experimental time window. Whereas DES was found to relax over a thousand times quicker, fully returning to the ground state by ∼1 ps. This simple and fundamental comparative study further demonstrates the effect and importance of symmetrically substituted sinapates for nature-inspired commercial
applications. References
1. M. D. Horbury, A. L. Flourat, S. E. Greenough, F. Allais and V. G. Stavros, Chem. Commun. , 2018, 54 , 936–939. 2. M. D. Horbury, E. L. Holt, L. M. M. Mouterde, P. Balaguer, J. Cebrián, L. Blasco, F. Allais and V. G. Stavros, Nat. Commun. , 2019, 10 , 4748.
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