Porous crystalline ruthenium complexes are oxygen sensors

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)(3)(2+) (pp = bpy (2,2'-bipyridine), phen (1, 10-phenanthroline) or 4.7-Me(2)phen (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 (A) over circle (3) per Ru in the crystals. The emission 2 intensity and lifetime quenching of [Ru(phen)(3)](tfpb)(2) displayed strictly linear (R-2 = 0.9996) Stern-Volmer behavior (plots of I-0/I and tau(0)/1 vs mole fraction of oxygen) with a slope of 2.43. A single exponential (tau = 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 mn, t(1/2)= 120 ms; at 518 mn, 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) cm(2)/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.