Building a Photocatalyst Library of MR-TADF Compounds with Tuneable Excited-State Redox Potentials

Epitomised by 4CzIPN, donor-acceptor (D-A) thermally activated delayed fluorescence (TADF) compounds based on the carbazoyl dicyanobenzene have now become widely used as they are sustainable photocatalyst alternatives to organometallic complexes owing to their similar optoelectronic properties to many of the iridium-based photocatalysts. Multi-resonant TADF (MR-TADF) compounds offer distinct advantages over D-A TADF compounds as they have more intense low-energy absorption bands, offering faster reaction kinetics, and are less sensitive to the polarity of the environment, mitigating undesired energy loss that typically accompanies the CT excited states of the photocatalysts. Here we report the assessment of strongly photoreducing boron- and nitrogen-doped MR-TADF compounds DABNA-1, tDABNA, CzBN and DtBuCzB across a range of benchmark photochemical reactions. The structural differences between each member of this library of photocatalysts enables modulation of their ground- and excited-state redox potentials. These photocatalysts performed competitively compared to the literature-known 4CzIPN, Ph-PTZ and fac-Ir(ppy)3.