Ultrafast dynamics of photo-excited 2-thiopyridone: Theoretical insights into triplet state population and proton transfer pathways.

Jesper Norell,Morgane Vacher,Michael Odelius

doi:10.1063/1.5143228

Jesper Norell, Morgane Vacher + Show 1 more

Open Access

https://doi.org/10.1063/1.5143228

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Abstract

Ultrafast non-adiabatic dynamics of the small heteroaromatic compound 2-thiopyridone has been studied with surface hopping simulations based on multi-configurational quantum chemistry. Initial excitation of the bright state is found to promptly relax to ) through in-plane motion. The subsequent dynamics are oppositely driven by out-of-plane motion, which results in both complex population transfers among all the available states and intersystem crossing predominantly through the “El-Sayed forbidden” ) to ) channel, through significant mixing of electronic excitation characters. Despite this complexity, the femto- to picosecond triplet population, expected from several spectroscopic measurements, is well described as a simple exponential decay of the singlet state manifold. No proton transfer is found in the reported trajectories, but two mechanisms for its possible mediation in previously reported experiments are proposed based on the observed structural dynamics: (i) ultrafast intra-molecular transfer driven by the initially coherent in-plane motion and (ii) inter-molecular solvent-mediated transfer driven by the out-of-plane modes that dominate the later motion.

Highlights

Due to the importance of light induced processes in biomolecules, in general, and in nucleic acids, in particular, the photochemistry of heteroaromatic compounds has been the subject of extensive investigations.[1]
The subsequent dynamics are oppositely driven by out-of-plane motion, which results in both complex population transfers among all the available states and intersystem crossing predominantly through the “El-Sayed forbidden” S1ðn; pÃ) to T2ðn; pÃ) channel, through significant mixing of electronic excitation characters
No proton transfer is found in the reported trajectories, but two mechanisms for its possible mediation in previously reported experiments are proposed based on the observed structural dynamics: (i) ultrafast intra-molecular transfer driven by the initially coherent in-plane motion and (ii) inter-molecular solvent-mediated transfer driven by the out-of-plane modes that dominate the later motion

Summary

INTRODUCTION

Due to the importance of light induced processes in biomolecules, in general, and in nucleic acids, in particular, the photochemistry of heteroaromatic compounds has been the subject of extensive investigations.[1]. We simulate the non-adiabatic molecular dynamics, including spin–orbit coupling induced transitions, of photo-excited 2-TP This provides a link between the excited-state dynamics probed in previous time-resolved measurements[18,20,21,22] and quantum chemical insights gained from previous simulations.[18,22,23,24,31] Our main goal is to identify inherent aspects of the ultrafast dynamics, both electronic and structural, which result in the observed triplet population and may drive ESPT along previously reported or alluded pathways at various timescales

COMPUTATIONAL DETAILS

Electronic states

Electronic dynamics

Proton transfer

CONCLUSIONS