We report crystalline mixed-ligand copper complexes with phenanthroline and isocyanides with almost millesecond emission lifetimes that are efficient dioxygen sensors. The oxygen sensitivity of the prototype ([Cu(CN-xylyl)2(dmp)]tfpb, dmp = 2,9-dimethyl-1,10-phenanthroline; CN-xylyl = 2,6-dimethylphenylisocyanide; tfpb = tetrakis(bis-3,5-trifluoromethylphenylborate) is 38 times better than that of [Ru(phen)3]tfpb2 (phen = 1,10-phenanthroline).

The novel terthiophene (3T) oligomer 6 and a series of cationic Ir(III) bis-cyclometalates [Ir(C∧N)2(N∧N)]PF69–12 were prepared. The synthesis, characterization, electrochemical, and photophysical properties are reported. The cyclometalating ligands (C∧N) are 2-phenylpyridinato (ppy) or the 3T oligomer (3T-ppy), asymmetrically capped in the 5 and 5″ positions with the ppy and mesityl groups. The diimine ligands (N∧N) are 2,2′-bipyridine (bpy) or 4-NO2-bipyridine (4-NO2-bpy). Hybrid metal-organic complexes 11 and 12 bear 3T-pendants ligated through the ppy cap, 10 and 12 contain NO2 functionalized diimines, whereas 9 contains neither. Structural characterization of 10 by single crystal X-ray diffraction confirms the presence of the NO2 substituent and pseudo-octahedral coordination geometry about the Ir(III) ion. Cyclic voltammetry highlights the large electron withdrawing effect of the NO2 substituent, providing an 850 mV shift toward lower potentials for the first diimine centered reduction of 10 and 12. Strong overlap of the intense π → π* absorptions of the 3T-pendants with Ir(III) charge transfer bands is evident in complexes of 11 and 12, precluding the possibility for selective excitation of either chromophore. Photoexcitation (λex = 400 nm) of the series affords strong luminescence from the 3T oligomer 6 and the unsubstituted 9, with ϕem = 0.11. In stark contrast the NO2 and 3T functionalized complexes 10–12 display near total quenching of luminescence. Computations of the ground and excited state electronic structure using density functional theory (DFT) and time-dependent DFT (TD-DFT) indicate that both the NO2 and 3T substituents play an important role in excited state deactivation of complexes 10–12. A substantial electronic contribution of the NO2 substituent results in stabilization of the diimine based molecular orbital (MO) and offers an efficient nonradiative decay pathway for the excited state. Spin–orbit coupling effects of the Ir(III) ion lead to efficient population of the low lying, nonluminescent, triplet states centered on the 3T-pendants.

A system pairing the luminescent core of [Ir(ppy)2L2]+ (ppy = 2-phenylpyridine) with simple hydrazino ancillary ligands (L = N2H4) has been prepared for the direct optical detection of carbon dioxide (CO2). Silver-assisted and silver-free techniques were used for the successful introduction of N2H4 into the [Ir(ppy)2Cl]2 coordination sphere at room temperature to give the corresponding biscyclometalated iridium(III) hydrazino species as either a CF3SO3– (OTf–, 2a) or Cl– (2b) salt. The silver-free route was accomplished by the direct replacement of the ligated Cl– using a slight excess of hydrazine. The luminescence profile of the cationic iridium(III) hydrazino complex 2a (λmax = 501 nm) undergoes a red shift (λmax = 524 nm), accompanied by a change in the peak shape during exposure to CO2 in solution. The spectral changes observed are attributed to the formation of the corresponding neutral carbazate species Ir(ppy)2(H2NNHCOO) (3) and are not consistent with protonation of the ligated hydrazine. Conversion of the hydrazino species to the carbazate species is solvent-dependent and irreversible. The hydrazino and carbazate species have been structurally characterized by single-crystal X-ray diffraction; both compounds exhibit long-lived and intense room temperature luminescence in solution with τ = 1.56 and 1.80 μs and ϕem = 0.42 and 0.45, respectively.

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 KSV 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 KSV 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, (KSV = 4.76; 4,7-Me2phen = 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.

New direct syntheses of [Pt(trpy)(NCCH3)](CF3SO3)22 (where trpy = 2,2′:6′,2′′-terpyridine) and [Pt(tBu3-trpy)(NCCH3)](CF3SO3)23 (where tBu3-trpy = 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine) via the displacement of acetonitrile from [Pt(NCCH3)4](CF3SO3)2 have been developed. The synthetic utility of 2 was investigated in reactions with triphenylphosphine (PPh3), 2,6-dimethylphenyl isocyanide (CN-Xyl), 2,5-dimethyl-2,5-diisocyanohexane (TM4), and tert-butyl isocyanide (CN-tBu). Whereas the expected substitution products were observed for reactions with PPh3, CN-Xyl, and CN-tBu, dealkylation of TM4 occurred to afford [Pt(trpy)(CN)](CF3SO3) 6. The structures of [Pt(trpy)L]2+ dications show little intermolecular interactions in the solid state, with the exception of the tBu3-trpy complex 3 which exists as head-to-tail dimers with a Pt–Pt distance of 3.29 Å. The cyano product 6 was found to stack in infinite chains of cations with a Pt–Pt distance of 3.45 Å.New direct syntheses of compounds of the type [Pt(trpy)(NCCH3)](CF3SO3)22 (where trpy = 2,2′:6′,2′′-terpyridine) via the displacement of acetonitrile from [Pt(NCCH3)4](CF3SO3)2 have been developed. The synthetic utility of 2 was investigated in reactions with triphenylphosphine and isocyanides. The products of these reactions along with the starting materials have been investigated with X-ray crystal structure analyses.

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 Ksv 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.

The complex [Ru(5,6-Me2Phen)3]tfpb2 has been examined as a solid-state benzene and oxygen sensor. The crystalline solid undergoes a reversible vapochromic shift of the emission λmax to higher energy in the presence of benzene. Additionally, in the presence of oxygen the solid exhibits linear Stern-Volmer quenching behavior. When simultaneously exposed to benzene vapor and oxygen the crystals uptake benzene which inhibits the diffusion of oxygen in the lattice; very little quenching is observed. However, when benzene is removed from the carrier gas, partial loss of benzene occurs and oxygen diffusion is restored resulting in quenching of the emission. The practicality of this crystalline solid as a benzene sensor was investigated by examination of a lower concentration of benzene vapor (0.76%).