The dependence of oxygen sensitivity on the molecular structures of Ir(iii) complexes and their application for photostable and reversible luminescent oxygen sensing

Abstract

Three Ir(III) complexes IrC1, IrC2, and IrC3 substituted with 4-(diphenylamino)phenyl (TPA), 4-(9H-carbazol-9-yl)phenyl (Cz1), and 9-phenyl-9H-carbazol-3-yl (Cz2) moieties were prepared and fully characterized as phosphorescent emitters. In comparison with Ir(ppy)₃, introduction of TPA, Cz1, and Cz2 moieties strongly improved the oxygen sensitivities of IrC1–IrC3. Short-decayed IrC1 with I₀/I₁₀₀ of 168.6 and K^app_SV of 202.2 bar⁻¹ in THF exhibited the highest sensitivity for oxygen. TPA and Cz moieties caused remarkable collision radius variations of the Ir(III) complexes with 2.13 ± 0.08 for σ_IrC1/σ_Ir(ppy)3, 1.24 ± 0.06 for σ_IrC2/σ_Ir(ppy)3, and 1.54 ± 0.08 for σ_IrC3/σ_Ir(ppy)3. For demonstrating the dependence of oxygen sensitivity on the molecular structure of the oxygen-sensitive probes (OSPs), the delocalization of spin populations (DSPs) has been applied for the first time to confirm the collision radius variations of Ir(III) complexes. Remarkable DSPs were found on the TPA, Cz1, and Cz2 moieties with the spin population (percentage of the spin population) of 0.23210 (11.61%), 0.08862 (4.43%), and 0.13201 (6.60%), respectively. And strong linear correlations (R² = 0.997) between the collision radius variations and spin population on TPA and Cz moieties were apparent. The DSPs could be used to describe the dependence of oxygen sensitivity on the molecular structure of the OSPs. For achieving real-time oxygen sensing, the photostability, oxygen sensing performance, and operational stability of IrC1–IrC3 and Ir(ppy)₃ immobilized in ethyl cellulose (EC) were investigated. The IrC1-EC film demonstrated outstanding photostability after 60 min of irradiation and excellent operational stability for continuous oxygen monitoring with no attenuation of the original emission intensity in 4000 s. This study quantified and analyzed the dependence of oxygen sensitivity on the molecular structure of Ir(III) complexes for the first time and illustrated a feasible approach to achieve high-efficiency sensors for real-time monitoring of oxygen.