Energy transfer Having demonstrated the potential of pDTCz-DPmS as a photoredox catalyst in reactions that proceed by both oxidative and reductive quenching mechanisms, we next explored this compound in the context of an energy transfer photocatalytic reaction. We first investigated the E/Z isomerization of stilbene (Figure ), following the conditions employed by Zhang et al. Reaction yields are shown in Table . The photocatalytic isomerization of alkenes is a well-documented process 34-36 that proceeds via a Dexter energy transfer mechanism. For Dexter energy transfer to be operational, there must be orbital overlap between the donor and acceptor, which can be achieved through bimolecular collisions in an intermolecular reaction. Additionally, spectral overlap between the emission of the energy donor (the photocatalyst) and absorption of the energy acceptor (the E-alkene) is required. Triplet energy levels of the PC and the substrate are typically used to crudely assess whether the energy transfer is thermodynamically feasible. To prevent photocatalyzed isomerization of the Z-alkene back to the E-alkene, the triplet state of the PC must be of intermediate energy to those of the configurational isomers. For stilbene, the ET are 2.2 eV and 2.5 eV, respectively,