Mesityl or imide acridinium photocatalysts: accessible versus inaccessible charge-transfer states in photoredox catalysis

A study on C9-imide acridinium photocatalysts with enhanced photoredox catalytic activity with respect to the well-established C9-mesityl acridinium salt is presented. The differences observed rely on the diverse accessibility of singlet chargetransfer excited states, which have been proven by CASPT2/CASSCF calculations, fluorescence and quenching studiesThe Boehringer Ingelheim Stiftung (Exploration Grant), the Deutsche Forschungsgemeinschaft (DFG), Spanish Government (CTQ2015-64561-R, CTQ2015-63997-C2, ENE2016-79608-C2-1-R) and Community of Madrid (2016-T1/AMB-1275) are acknowledged. The authors wish to thank ’’Comunidad de Madrid’’ for its support to the FotoArt-CM Project (S2018/NMT-4367) through the Program of R&D activities between research groups in Technologies 2013, co-financed by European Structural Fun