Received November 15, 2006

Revised Manuscript Received October 27, 2007

Abstract:

Several highly emissive, crystalline salts (ClO₄^-, PF₆^-, BF₄^-, B(C₆F₅)₄^-, and tfpb^-; B(C₆F₅)₄^- = tetrakis(pentafluorophenyl)borate; tfpb^- = tetrakis(bis-3,5-trifluoromethylphenylborate) of the Ru(pp)₃²⁺ (pp = bpy (2,2'-bipyridine), phen (1,10-phenanthroline) or 4,7-Me₂phen (4,7-dimethyl-1,10-phenanthroline) lumophore have been tested as oxygen sensors. Oxygen detection by luminescence quenching correlates with the void space in the crystalline lattice, particularly in the case of [Ru(phen)₃](tfpb)₂ which has channels occupying approximately 136 ų per Ru in the crystals. The emission intensity and lifetime quenching of [Ru(phen)₃](tfpb)₂ displayed strictly linear (R² = 0.9996) Stern-Volmer behavior (plots of I₀/I and ₀/ vs mole fraction of oxygen) with a slope of 2.43. A single exponential ( = 640 nsec, pure nitrogen; 190 nsec, pure oxygen) is observed for the emission intensity decay for all oxygen concentrations. The time dependence of the emission caused by a step function air pressure drop is significantly affected by changing the light penetration depth when different excitation wavelengths are used (at 400 nm, t_1/2 = 120 ms; at 518 nm, t_1/2 = 2200 ms). These experiments are consistent with the diffusion of oxygen molecules in and out of [Ru(phen)₃](tfpb)₂ crystals with a diffusion coefficient on the order of 10^-7-10^-8 cm²/s. The technological significance of these crystalline oxygen sensors was demonstrated by long-term stability studies and by the successful calibration of a ballprobe sensor coated with crystalline [Ru(phen)₃](tfpb)₂ against a dissolved oxygen Clark electrode using a partial least-squares (PLS) model with a single principle component.

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