Homogeneous Photocatalytic H Production Using a Ru Bathophenanthroline Metal-to-Ligand Charge-Transfer Photosensitizer.

The prototypical [Ru(bpy) ] (bpy=2,2'-bipyridine) photosensitizer has been previously demonstrated to be labile in aqueous photocatalytic solutions, especially in the presence of coordinating electron donors. Here, an alternative Ru molecular sensitizer, [Ru(dpp) ] (dpp=4,7-diphenyl-1,10-phenanthroline or bathophenanthroline), is described, which is considerably more stable than its bpy congener, allowing enhanced photocatalysis metrics in conjunction with a cobalt glyoxime ([Co(dmgH) pyCl], dmgH=dimethylglyoxime, py=pyridine) water reduction catalyst and N,N-dimethyl-p-toluidine (DMT) as the sacrificial donor in a 1:1 mixture of CH CN/H O. Photoluminescence studies revealed that DMT reductively quenches the excited state of [Ru(dpp) ] with a bimolecular rate constant of k =4.9×10  m  s . The rate constant measured for electron transfer from the reduced sensitizer to the [Co(dmgH) pyCl] was found to be near the diffusion limit, k =2.4×10  m  s . H production by photocatalysis was independently monitored by using a high-throughput photochemical reactor equipped with pressure transducers, gas chromatogram, and a mass spectrometer for detection; this illustrated that the composition yields high turnover numbers (TONs), approaching 10 000 (H /Ru) with respect to the sensitizer and deuteration studies using D O confirmed that H is primarily produced from protons derived from water in these systems.