Tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) dichloride complex (Ru(ddp)) is a widely used probe for luminescent detection and quantitation of oxygen. The fluorescence of the dye (abs. λmax 455 nm, luminescence λmax 613 nm) is strongly reduced by molecular oxygen due to dynamic quenching, making Ru(dpp) a viable oxygen probe based on either measurement of intensity or decay time. Ru(ddp) has been used for fiber optic sensors, studies on oxygen in skin and skin tumors, measurement of oxygen flux through skin, and for oxygen imaging. Ruthenium-tris(4,7-diphen?yl-1,10-phenanthroline) dichloride (Ru(dpp)) has been widely used as a probe for luminescent detection and quantitation of oxygen. The fluorescence of the dye (abs. λmax 455 nm, luminescence λmax 613 nm) is strongly reduced by molecular oxygen due to dynamic quenching, making Ru(dpp) a viable oxygen probe based on either measurement of intensity or decay time. Ru(ddp) has been used for fiber optic sensors, studies on oxygen in skin and skin tumors, measurement of oxygen flux through skin, and for oxygen imaging