The synthesis of two new heteroleptic Cu(I) photo sensitizers (PS), [Cu(Xantphos)(NN)]PF6 (NN = biq = 2,2'-biquinoline, dmebiq = 2,2'-biquinoline-4,4'-dimethyl ester; Xantphos = 4,5bis(diphenylphosphino)-9,9-dimethylxanthene), along with the associated structural, photophysical, and electrochemical properties, are described. The biquinoline diimine ligand extends the PS light absorbing properties into the visible with a maximum absorption at 45S and 505 nm for NN = biq and dmebiq, respectively, in CH2Cl2 solvent. Following photoexcitation, both Cu(I) PS are emissive at low energy, albeit displaying stark differences in their excited state lifetimes (tau(MLCT) = 410 +/- 5 (biq) and 44 +/- 4 ns (dmebiq)). Cyclic voltammetry indicates a Cu-based HOMO and NN-based LUMO for both complexes, whereby the methyl ester substituents stabilize the LUMO within [Cu(Xantphos)(dmebiq)(+)] by similar to 0.37 V compared to the unsubstituted analogue. When combined with H2O, N,N-dimethylaniline (DMA) electron donor, and cis-[Rh(NN)(2)Cl-2]PF6 (NN = Me(2)bpy = 4,4'-dimethyl-2,2'-bipyridine, bpy = 2,2'-bipyridine, dmebpy = 2,2'-bipyridine-4,4'-dimethyl ester) water reduction catalysts (WRC), photocatalytic H-2 evolution is only observed using the [Cu(Xantphos)(biq)](+) PS. Furthermore, the choice of cis-[Rh(NN)(2)Cl-2]+ WRC strongly affects the catalytic activity with turnover numbers (TONRh, = mol H-2 per mol Rh catalyst) of 25 +/- 3, 22 +/- 1, and 43 +/- 3 for NN = Me(2)bpy, bpy, and dmebpy, respectively. This work illustrates how ligand modification to carefully tune the PS light absorbing, excited state, and redox-active properties, along with the WRC redox potentials, can have a profound impact on the photoinduced intermolecular electron transfer between components and the subsequent catalytic activity.