Ultrafast intersystem crossing in xanthone from wavepacket dynamics simulations

29 September 2021, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Most aromatic ketones containing first-row elements undergo unexpectedly fast intersystem crossing in few tens of picosecond and a quantum yield close to unity. Among them, xanthone (9H-xanthen-9-one) possesses one of the fastest intersystem crossing rates of ~1.5 ps, despite containing only first-row elements. The exact mechanism of this unusually fast singlet-triplet transition is still under debate. Here, we perform a complete wavepacket dynamics simulation of the internal conversion and intersystem crossing reactions of xanthone in the gas phase. We show that xanthone follows El-Sayed's rule for intersystem crossing. From the second singlet excited state, the mechanism is sequential: (i) an internal conversion between singlets 1pipi*-1npi* (~0.14 fs), (ii) an intersystem crossing 1npi*-3pipi* (~1.8 ps), and (iii) an internal conversion between triplets 3pipi*-3npi* (~27 ps). Each transfer finds its origin in a barrierless access to electronic state intersections. These intersections are close to minimum energy structures, allowing for an efficient radiationless transition from 1pipi* to 3npi*.

Keywords

photochemistry
wavepacket dynamics
aromatic ketones
intersystem crossing
non-radiative decay

Supplementary materials

Title
Description
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Title
Supporting Information: Ultrafast intersystem crossing in xanthone from wavepacket dynamics simulations
Description
Model Hamiltonian form and fitting parameters, computational details, a kinetic model for the fitting of diabatic populations and potential energy surfaces cuts.
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