Ultrafast intersystem crossing in xanthone from wavepacket dynamics

10 December 2021, Version 3
This content is a preprint and has not undergone peer review at the time of posting.


Most aromatic ketones containing first-row elements undergo unexpectedly fast intersystem crossing in few tens of picoseconds and a quantum yield close to unity. Among them, xanthone (9H-xanthen-9-one) possesses one of the fastest singlet-triplet rates of ~1.5 ps. The exact mechanism of this unusually fast transition is still under debate. Here, we perform the wavepacket dynamics of the photochemistry of xanthone in the gas phase and in polar solvents. 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* (85 fs), (ii) an intersystem crossing 1npi*-3pipi* (2.0 ps), and (iii) an internal conversion between triplets 3pipi*-3npi* (602 fs). Each transfer finds its origin in a barrierless access to electronic state intersections. These intersections are close to minimum energy structures, allowing for efficient transitions from the initial singlet state to the triplets.


wavepacket dynamics
aromatic ketones
intersystem crossing
non-radiative decay

Supplementary materials

Supporting information for: Ultrafast intersystem crossing in xanthone from wavepacket dynamics
The supporting information is available containing the form and parameters of the model hamiltonian, the computational details for electronic structure and quantum dynamics simulations, the vibrationally resolved absorption spectrum and its interpretation, the time evolution of populations in gas phase and the first-order kinetic model behind, the 1D potential energy curves along each normal mode, the Cartesian coordiantes of the optimized structures in gas phase, the molecular dynamics simulations and the quantum dynamics in water.


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