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Intersystem crossing driven by vibronic spin-orbit coupling: a case study on psoralen.
Jörg Tatchen1, Natalie Gilka, Christel M Marian
1Institute of Theoretical and Computational Chemistry, Heinrich Heine University, Universitätsstr. 1, D-40225 Düsseldorf, Germany.
Physical Chemistry Chemical Physics : PCCP
|May 23, 2009
Summary
Intersystem crossing (ISC) rate constants for psoralen were computed, revealing vibronic spin-orbit coupling significantly influences triplet state population. This mechanism is key for understanding psoralen
Area of Science:
- Quantum Chemistry
- Photochemistry
- Molecular Spectroscopy
Background:
- Psoralen's photochemistry is crucial for understanding its biological effects.
- Intersystem crossing (ISC) is a key process in determining triplet state yields.
- Spin-orbit (SO) coupling plays a vital role in facilitating ISC.
Purpose of the Study:
- To compute intersystem crossing (ISC) rate constants for 7H-furo[3,2-g][1]benzopyran-7-one (psoralen).
- To elucidate the contributions of direct and vibronic spin-orbit (SO) coupling to ISC.
- To explain the observed triplet quantum yields of psoralen in polar protic media.
Main Methods:
- Utilized the Fermi golden rule and harmonic approximation with a pure-spin Born-Oppenheimer basis.
- Employed (time-dependent) density functional theory and DFT/multireference configuration interaction for electronic structure calculations.
- Applied the one-center mean-field approximation for SO coupling and numerical differentiation for vibronic SO couplings.
Main Results:
- Direct SO coupling yields ISC rate constants of approximately 10^10 s^-1 for S2 --> T1 transitions.
- Vibronic SO coupling leads to S1 --> T1 ISC rate constants of approximately 3 x 10^8 s^-1.
- S1 --> T3 ISC rates were estimated at approximately 10^7 s^-1.
Conclusions:
- The primary mechanism for psoralen's high triplet quantum yields in polar protic solvents is S1 --> T (pi --> pi*) ISC.
- Vibronic SO coupling-driven (pi --> pi*)/(pi --> pi*) ISC is a common pathway for triplet state population in heteroaromatic systems.
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