The d⁸ complexes A[Au(C^C)(CN)₂] and A₂[Pt(C^C)(CN)₂] (where C^C = 4,4′-di-tert-butylbiphenyl-2,2′-diyl and A⁺ = NBu₄⁺, K⁺) were synthesized from [Au(C^C)Cl]₂ and [Pt(C^C)COD], which were themselves obtained from Sn(C^C)ⁿBu₂. These complexes are bright photoemitters but exhibit remarkable differences in the origin of their photoluminescence. The tin complex Sn(C^C)ⁿBu₂ displays blue/white photoluminescence originating from an admixture of transitions. In contrast, the gold complexes exhibit green, long-lived phosphorescence (lifetimes up to 100 μs), which theoretical calculations attribute to ³IL(C^C) transitions. Although the platinum complexes show similar absorption and emission energies, theoretical calculations indicate an admixture with ³MLCT character in their emissive states. This is evidenced by (i) luminescence lifetimes up to 1 order of magnitude shorter than those of the gold complexes under similar conditions; (ii) a greater contribution from fluorescence with respect to phosphorescence in solution, and (iii) reduced susceptibility to ³O₂ quenching, a consequence of the shorter triplet-state lifetime. The combination of water solubility, efficient ISC, and a long-lived triplet state with high sensitivity to dissolved O₂ endows K[Au(C^C)(CN)₂] with excellent catalytic activity in the photo-oxidation of p-bromothioanisole. This result underscores the potential of this class of Au(III) salts for photocatalysis in green solvents.