DiICz MR-TADF emitters as potent energy transfer photocatalysts

Photoinduced energy transfer (PEnT) reactions are a subset of photochemical reactions that involve the indirect photoactivation of substrates following an energy transfer from a photoexcited sensitizer/photocatalyst. Examples of PEnT reactions include E/Z isomerizations, [2 + 2] cycloadditions, and sigmatropic shifts. Here we introduce a family of diindolocarbazole (DiICz) multi-resonant thermally activated delayed fluorescent (MR-TADF) photocatalysts (PCs), DiICztBu₄, DiICzMes₄, DiICztBuCz₄, and DiICztBuDPA₄, which have relatively high triplet energies (E _T). We cross-compare their photocatalytic behavior and that of relevant literature reference PCs' in five distinct PEnT reactions. We demonstrate that the use of the DiICz PCs consistently leads to more rapid reaction rates and higher yields compared to the widely used 4CzIPN. DiICztBu₄, DiICzMes₄, and DiICztBuCz₄ possess similar E _T but decreasing singlet-triplet energy gaps, ΔE _ST, enabling for the first time a comparison of the dependency of both the reaction kinetics and the final yield on this photophysical parameter. We observed that when the reaction kinetics are fast, there is little sensitivity to quenching of the excited PC by oxygen, implying that Dexter Energy Transfer (DET) to the substrate is competitive with DET to oxygen. Importantly, this means that some of the DET reactions using these PCs can be performed in air without adversely affecting reaction yield.