Thus far, we have explored four intramolecular PEnT reactions. To expand the portfolio of available reactions we next investigated an example of a bimolecular cross-coupling reaction. This is frequently done by combining the photocatalytic cycle with a Ni-mediated crosscoupling reaction. In such dual-catalyzed reactions, the PC can either be involved in a PET mechanism, a so-called metallaphotoredox reaction, or in a PEnT reaction to sensitize the Ni co-catalyst by DET after it has undergone oxidative addition and transmetallation steps. This photoactivation accelerates the reductive elimination of the product. One such crosscoupling reaction where the PC is purported to engage in DET is an esterification involving aryl halides being cross-coupled with carboxylic acids where Welin et al. used fac-Ir(ppy)3 as the PC (ET(fac-Ir(ppy)3) = 2.58 eV). In this cross-coupling reaction, an undesired side product is lactone 2 (Table ). Several groups have employed organic PCs like 4DPAPN or SACR-IPTZ for this reactions (Figure ). 4DPAPN, after optimization of the reaction conditions, yielded 91% of 4-(trifluoromethyl)phenyl benzoate in the cross-coupling of benzoic acid with 4-bromobenzotrifluoride as substrates. With the same substrates but under slightly different conditions, Welin et al. reported an 86% yield using fac-Ir(ppy)3 as the PC. The reaction photocatalyzed using SACR-IPTZ yielded 99% of the coupled product between 5bromophthalide and benzoic acid, and no protodehalogenated product was observed. a 5-Bromophthalide (0.188 mmol, 1.0 equiv.), benzoic acid (0.301 mmol, 1.6 equiv.), 2,2,6,6tetramethylpiperidine (TMP) (0.375 mmol, 2.0 equiv.), Ni source (0.011 mmol, 6 mol%), 4,4'di-tert-butyl-2,2'-bipyridine (dtbbpy) (0.013 mmol, 7 mol%) and PC (0.004 mmol, 2 mol%) in DCM (0.09 M). Yields were determined by 1 H NMR spectroscopy using 1,3,5-trimethoxy benzene as the internal standard.