Particularly, since 2016 the organic compound 2,4,5,6-tetra(9H-carbazol-9yl)isophthalonitrile, 4CzIPN, (Figure ) has become a popular choice as a photocatalyst. First developed as an emitter for organic light-emitting diodes (OLEDs), 11 this compound possesses remarkably similar photophysical properties to the commonly used [Ir(dF(CF3)ppy)2(dtbbpy)]PF6 [(dF(CF3)ppy) = 2-(2,4difluorophenyl)-5-(trifluoromethyl)pyridinato and dtbbpy = 4,4′-di-tert-butyl-2,2′bipyridine] (Figure ). 4CzIPN absorbs into the visible region of the electromagnetic spectrum (λabs = 435 nm in MeCN), 10 has a long-lived excited state lifetime as it shows thermally activated delayed fluorescence (TADF), (τp = 18.7 ns and τd = 1390 ns in where τp and τd refer to the prompt and delayed fluorescence lifetimes, respectively), and it possesses a suitable range of redox potentials (Table ). 4CzIPN is composed of an isophthalonitrile acceptor core, decorated with four carbazole electron donor moieties. The steric interactions between adjacent carbazole groups create large torsions between the donor groups to the isophthalonitrile unit. The resultant highly twisted structure ensures that the highest occupied molecular orbital (HOMO) is localized on the donor groups while the lowest unoccupied molecular orbital (LUMO) is located on the acceptor phthalonitrile moiety, leading to a small exchange integral and a correspondingly small singlet-triplet excited state energy gap, ΔEST. The suitably small ΔEST is required for the observed TADF associated with this compound. 15 A particular benefit of donor-acceptor organic TADF compounds such as 4CzIPN lies in the facility to modulate their optoelectronic properties through modification of the structures of the donor or acceptor units, which, due to their relatively small electronic coupling, impact mostly independently the This facile tuning of the photophysical and electrochemical properties is an attractive and beneficial quality, one that historically has been challenging to achieve with organic photocatalysts. 17 To date, there are now over 200 reports that demonstrate the use of 4CzIPN and related donor-acceptor compounds, such as 4DPAIPN (Figure ), as effective photocatalysts. Inspired by this report, we identified a donor-acceptor sulfone-containing compound, 9,9′-(sulfonylbis(pyrimidine-5,2-diyl))bis(3,6-di-tert-butyl-9H-carbazole), pDTCz-DPmS, (Figure ), that we had previously developed as a TADF emitter in OLEDs, 21 for use as a potential photocatalyst. This compound possesses a wider ground state redox window, a longer delayed lifetime and is significantly more (photo)reducing than 4CzIPN (Table ).