Design and Application of Novel, Visible-Light Acridinium-type Organophotocatalysts

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This project focusses on the design of novel acridinium-based structures as organophotocatalysts with improved oxidative and catalytic properties in their exited state for the development of valuable oxidative photocatalysis. Visible light photoredox catalysis has arisen as a powerful synthetic tool, offering access to unique reactivities. Besides transition-metal photosensitizers, organic dyes have recently been attracted great attention as photoredox catalysts, from which acridinium salts shine as one of the most powerful organophotocatalyst-type oxidants. However, their intrinsic instability and synthetic accessibility limit the structures to C9-aryl substituted species. In this project, new synthetic methods, including novel oxidative C-H functionalization approaches, to acridinium salts bearing C9-amide and amide-isosteric heterocycles will be developed. We have recently demonstrated that related C9-imide acridinium salts present enhanced photoactivities than standard C9-mesityl acridinium salts. However, their substitution pattern is constrained for which the proposed methods and structures will overcome the current tuneability issues. This project also aims at a better understanding of the photophysical properties and performance of the proposed new catalysts in order to identify improved highly active structures. The information obtained will be used to re-design new catalysts, whose activity will be evaluated in challenging visible light photocatalytic reactions, such as hydrofunctionalization of to date still highly demanding olefinic substrates, desilylative coupling reactions involving C(sp2)-Si bonds or selective radical cyclizations towards valuable heterocycles.