Emission spectroscopy of Ru(bpy)(2)dppz(2+) in Nafion. Probing the chemical environment in cast films

The incorporation of Ru(bpy)(2)dppz(2+) (dppz = dipyrido[3,2-a:2',3'-c]phenazine) into Nafion coatings was monitored in situ by electronic absorption, steady-state emission, and lifetime measurements. Whereas the aqueous loading solution does not show any luminescence (the emission of Ru(bpy)(2)dppz(2+) in nonaqueous solvents is completely quenched by water), strong emission was detected immediately after immersion of the Nafion coating. The emission decay is triexponential, with two long-lived components (tau = 900 and 300 ns) dominating a fast decay (tau = 50 ns). Emission intensities, lifetimes, and lifetime distributions depend strongly on the loading level, owing both to self-quenching and environmental changes brought about by increases in the concentration of the complex in the film. Owing to the remarkable efficiency of excited-state deactivation attributable to dppz-H2O hydrogen bonding, Ru(bpy)(2)dppz(2+) is an extremely sensitive probe of accessible water structures in Nafion.