We have shown that crystals of the highly emissive copper(I) compounds [Cu(POP)(dmp)]tfpb, [Cu(xantphos)(dmp)]tfpb, [Cu(xantphos)(dipp)]tfpb, and [Cu(xantphos)(dipp)]pftpb, (where POP = bis[2-(diphenylphosphino)phenyl]ether; xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene; dmp = 2,9-dimethyl-1,10-phenanthroline; dipp = 2,9-diisopropyl-1,10-phenanthroline (dipp); tfpb(-) = tetrakis(bis-3,5-trifluoromethylphenylborate); and pftpb = tetrakis(pentfluorophenyl)borate) are oxygen gas sensors. The sensing ability correlates with the amount of void space calculated from the crystal structures. The compounds exhibit linear Stern-Volmer plots with reproducible K(SV) constants from sample to sample; these results reinforce the observations that the sensing materials are crystalline and the sensing sites are homogeneous within the crystals. The long lifetime (∼30 μs), high emission quantum yield (ϕ = 0.66), appreciable K(SV) value (5.65), and very rapid response time (51 ms for the 95% return constant) for [Cu(xantphos)(dmp)]tfpb are significantly better than those for the [Cu(NN)(2)]tfpb complexes studied previously and compare favorably with [Ru(4,7-Me2phen)(3)](tfpb)(2), (K(SV) = 4.76; 4,7-Me(2)phen = 4,7-dimethyl-1,10- phenanthroline). The replacement of precious metals (like Ru or Pt) with copper may be technologically significant and the new compounds can be synthesized in one or two steps from commercially available starting materials. The strictly linear Stern-Volmer behavior observed for these systems and the absence of a polymer matrix that might cause variability in sensor to sensor sensitivity may allow a simple single-reference point calibration procedure, an important consideration for an inexpensive onetime limited use sensor that could be mass produced.
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-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 Å3 per Ru in the crystals. The emission 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 τ0/τ vs mole fraction of oxygen) with a slope of 2.43. A single exponential (τ = 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.
On-site determination of leaded paint in houses is important for minimizing the costs of renovations. A simple fiber-optic probe suitable for remote elemental analysis using laser-induced breakdown spectroscopy has been developed for this purpose and is used to determine the lead concentration in samples of dry paint. Optical fibers transport the laser pulse to the sample and transfer the emission signal to the spectrometer. The use of separate excitation and collection fibers allows coupling of the probe to a conventional spectrometer using simple optics. The measurement takes less than 1 min to perform, requires no sample preparation, and can be made through overlayers of non-lead-containing paint. The limit of detection is 0.014% Pb in latex paint, on a dry weight basis, with relative sample standard deviations of 5−10%.
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