Four iridium(III)-containing coordination polymers 1–4 using Ir(ppy)₂(H₂dcbpy)PF₆ (L-H₂, ppy = 2-phenylpyridine, H₂dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) as the bridging ligand, [ZnL₂]·3DMF·5H₂O (1), [CdL₂(H₂O)₂]·3DMF·6H₂O (2), [CoL₂(H₂O)₂]·2DMF·8H₂O (3) and [NiL₂(H₂O)₂]·3DMF·6H₂O (4), have been synthesized and structurally characterized. The emissions from 1–4 are ascribed to a metal-to-ligand charge transfer transition (MLCT). The absolute emission quantum yields for 1–4 in single crystals were measured in air to be 0.274, 0.193, 0.001 and 0.002, respectively. The noteworthy oxygen-sensing properties of 1–4 as well as L-H₂ in a single crystal were also evaluated. The Stern–Volmer quenching constant, K_SV values, of 1–4 and L-H₂ can be deduced to be 0.834, 2.820, 1.328, 1.111 and 2.476, respectively. The results show promising K_SV values (e.g.2) that are competitive or even larger than those of many known Ir-complexes. Moreover, the short response time (e.g. compound 2) and recovery times toward oxygen of 1–4 have been measured in their single crystal forms. The reversibility experiments for 1–4 were carried out for seven repeated cycles. As a result, >75% recovery of intensity for 1 and 2 on each cycle demonstrates a high degree of reproducibility during the sensing process. It should be noted that iridium(III)-containing coordination polymers with high emission intensity and notable oxygen sensing properties are obscure, especially in the single crystal form. This, in combination with its fine reversibility, leads to success in single crystal oxygen recognition based on photoluminescence imaging. The detection limit could be 0.50% for gaseous oxygen. Moreover, the temperature effect of compound 2 in a single crystal upon application as an oxygen sensor was expected.

Four new lead(II)–iridium(III) heterobimetallic coordination frameworks, i.e., [Pb₂(L)₄(DMF)₂]·ClO₄·2DMF·13H₂O (1·DMF), [Pb(L)₂·H₂O]·ClO₄·3C₃H₆O·3H₂O (1·Acetone), [Pb(L)₂·H₂O]·3C₃H₆O·3H₂O·CH₃CN (2·Acetone), and [Pb₄(L)₄I₄·(DMF)₂]·10H₂O (3·DMF), where is L-H₂ = Ir(ppy)₂(H₂dcbpy)PF₆, ppy = 2-phenylpyridine, and H₂dcbpy = 4,4′-dicarboxy-2,2′-bipyridine, have been synthesized and structurally characterized using elemental analyses, IR spectroscopy, optical spectroscopy, and single-crystal X-ray diffraction. Heavy atoms, i.e. lead(II) atoms, were introduced to the frameworks and coordinated with the chromophore to promote an efficient intersystem crossing from the singlet to the triplet ³MLCT excited state and further promote sensitivity to oxygen. The emissions of 1·DMF, 1·Acetone, 2·Acetone and 3·DMF (referred to hereafter as 1·DMF–3·DMF) were ascribed to metal-to-ligand charge transfer transitions (MLCTs). These four compounds, using phosphorescence based detection, were able to detect oxygen sensitively in real gas, and their noteworthy oxygen-sensing properties were also evaluated. The quenching constants, or K_SV values, between 1·DMF–3·DMF and oxygen, can be deduced to be 1.44, 1.60, 2.85, and 5.11, respectively. The minimum detectable concentrations (LODs) of oxygen for 1·DMF–3·DMF were calculated to be 0.65%, 0.70%, 0.61%, and 0.52%, respectively, from three times the signal to noise ratio. Moreover, taking 3·DMF as an example, short response (50 s) and recovery times (24 s) toward oxygen have been measured. It should be noted that the evaluated recovery time for 3·DMF is even shorter than those reported for rare-earth MOF films. The gas sensing properties, including sensitivity, sensing linearity, reproducibility, matrix effect, cross-sensitivity effect, temperature effect, and long-term stability, were investigated. Finally, in order to spark a broad spectrum of interest in terms of an application, 3·DMF was mixed with a commercial dye, Coumarin 480 (C480), to form a ratiometric oxygen sensor for the analysis of real gas in air.

A simple and sensitive biosensor array based on phosphorescence detection that is able to detect oxygen and glucose in human serum, respectively, has been developed. We demonstrate an electrochemical method as a fast, effective, tunable, and versatile means of growing phosphorescence sensing material. This sensing material, crystalline iridium(III)–Zn(II) coordination polymers, namely Ir–Zn_e, was grown on a stainless steel mesh and then doped in a sol–gel matrix. The emission of Ir–Zn_e was ascribed to a metal-to-ligand charge transfer transition (MLCT). The noteworthy oxygen-sensing properties of Ir–Zn_e were also evaluated. The optimal oxygen-sensing conditions of Ir–Zn_e with a deduced K_SV value of 3.55 were 5 V and 30 °C for 1 hour. Moreover, the short response time (23 s) and the recovery time (21 s) toward oxygen have been measured. The reversibility experiment was carried out for eleven cycles. The resulting >70% recovery of intensity for Ir–Zn_e on each cycle demonstrated a high degree of reproducibility during the sensing process. The detection limit could be 0.050% for gaseous oxygen. The sensing substrate was subsequently built up under glucose oxidase encapsulated in hydrogel and then immobilized on an egg membrane by the layer-by-layer method. Once the glucose solution was injected into this array, oxygen content depleted simultaneously with a concomitant increase in the phosphorescence of coordination polymers. The linear dynamic range for the determination of glucose was 0.1–6.0 mM, the correlation coefficient (R²) was 0.9940 (y = 0.75 [glucose] + 0.539), and the response time was less than 120 s. The minimum detectable concentration for glucose was calculated to be 0.05 mM from three times signal to noise. The photophysical properties of the sensing material and the effects of buffer concentration, pH, interference, matrix effect, temperature, and the stability of the biosensor array have also been studied in detail. The biosensor array was successfully applied to the determination of glucose in human serum.