Void Space Containing Crystalline Cu(I) Phenanthroline Complexes As Molecular Oxygen Sensors

We have shown that crystals of a number of emissive copper compounds of the form [Cu(NN)2]X (X = BF4 −, tfpb−) (where NN = 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (dmp), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bdmp), 2,9-diisopropyl-1,10-phenanthroline (dipp), 2,9-ditert-butyl-1,10-phenanthroline (dbp); tfpb− = tetrakis(bis-3,5-trifluoromethylphenylborate) are oxygen sensors, if they contain void space. All of the tfpb− salts were found to be oxygen sensors reinforcing the idea that bulky counterions can produce void space and obviate the need for a support material in solid-state photoluminescent oxygen sensors. The reponse time for the X = tfpb− and NN = dipp complex was measured to be fast (280 ms (95% of final value)). The first solid-state quantum yields and lifetimes are reported for the [Cu(NN)2]X systems and are found to be approximately 10 times larger than those observed in solution-state measurements. The linear Stern−Volmer plots with highly reproducible K sv constants observed from sample to sample and day to day reinforce the observations that the sensing materials are crystalline, stable to air and light, and the sensing sites are homogeneous within the crystals.