Rational Design of Triplet Sensitizers for the Transfer of Excited State Photochemistry from UV to Visible

Time Dependent Density
Functional Theory has been used to assist
the design and synthesis of a series thioxanthone triplet sensitizers.
Calculated energies of the triplet excited state (ET) informed both the type and position of auxochromes
placed on the thioxanthone core, enabling fine-tuning of the UV–vis
absorptions and associated triplet energies. The calculated results
were highly consistent with experimental observation in both the order
of the λmax and ET values.
The synthesized compounds were then evaluated for their efficacies
as triplet sensitizers in a variety of UV and visible light preparative
photochemical reactions. The results of this study exceeded expectations;
in particular [2 + 2] cycloaddition chemistry that had previously
been sensitized in the UV was found to undergo cycloaddition at 455
nm (blue) with a 2- to 9-fold increase in productivity (g/h) relative
to input power. This study demonstrates the ability of powerful modern
computational methods to aid in the design of successful and productive
triplet sensitized photochemical reactions.