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The effects of dissolved metal salts on the excited-state dynamics of acetophenone in solution have been explored using ultrafast transient absorption spectroscopy at two UV excitation wavelengths. In the absence of metal ions, the S1(nπ*) transition of acetophenone is excited at 320 nm, with intersystem crossing (ISC) occurring with a time constant τISC = 5.95 ± 0.47 ps in acetonitrile solution. Excitation at 280 nm accesses the S2(ππ*) state, which internally converts (<0.2 ps) to S1 before undergoing ISC with τISC = 4.36 ± 0.14 ps. Coordination to Mg2+ ions makes the S2 state accessible to excitation at 320 nm, with the rate of S2 → S1 internal conversion reducing 3-fold, but the ISC rate increasing. These changes to the excited-state energies and dynamics of this model photosensitizer indicate that dissolved metal salts could modify the photochemistry of synthetically useful homogenous photocatalytic systems.
Bibliographical noteFunding Information:
We gratefully acknowledge financial support from EPSRC Grant EP/R012695/1. The ultrafast laser laboratory at the University of Bristol was established with funding from ERC Advanced Grant CAPRI 290966. We thank Dr. Ravi Kumar Venkatraman for valuable discussions in the early stages of this research.
© 2021 American Chemical Society.
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