The influence of molecular structure on collision radius for optical sensing of molecular oxygen based on cyclometalated Ir(iii) complexes

Three triphenylamine (TPA) substituted cyclometalated Ir(iii) complexes IrA1, IrA2, and IrA3 based on Ir(ppy)₃ were synthesized and applied as phosphorescent probes for the monitoring of molecular oxygen. The phosphorescence intensity of all the Ir(iii) complexes in tetrahydrofuran (THF) was gradually quenched with an increase of oxygen concentration. The increase of TPA substituents on the meta-position of 2-phenylpyridine (IrA1-IrA3) gradually improved the oxygen sensitivity of cyclometalated Ir(iii) complexes. IrA3 showed the highest oxygen sensitivity in THF with a K^app_SV of 204.8 bar⁻¹ and a limit of detection (LOD) of 0.27 mbar. The relationship between molecular structure and the collision radiuses (σ) of all the Ir(iii) complexes has been investigated on the basis of the Demas model and the fundamental expression of luminescence quenching systems by oxygen. The ratio of collision radiuses are σ_IrA1/σ_Ir(ppy)3 = 1.27 ± 0.05, σ_IrA2/σ_Ir(ppy)3 = 1.72 ± 0.10, and σ_IrA3/σ_Ir(ppy)3 = 2.13 ± 0.07, respectively. The introduction and increase of TPA substituents can obviously increase the collision radiuses of cyclometalated Ir(iii) complexes which leading to potential oxygen sensitivity. And the incremental effect of collision radiuses caused by the introduction of TPA substituents resulted in outstanding oxygen sensitivity of IrA3. The results demonstrate for the first time evidence between molecular structure and oxygen sensitivity of the emitters for optical sensing.

The triphenylamine substituents increased the collision radiuses of cyclometalated Ir(iii) complexes which leading to potential oxygen sensitivity.

A rare example of a compact heteroleptic cyclometalated iridium(iii) complex demonstrating well-separated dual emission

Cationic heteroleptic Ir(iii) complexes [Ir(C^N)₂(NN)][PF₆] exhibit unique singlet–triplet dual emission in solution with two well separated emission bands.

Colorimetric and luminescent bifunctional iridium(III) complexes for the sensitive recognition of cyanide ions

Two new cyclometalated iridium(III) complexes [(ppy)₂Irppz]Cl (1) and [(ppy)₂Irbppz]Cl (2) (where ppy=2-phenylpyridine, ppz=4,7-phenanthrolino-5,6:5,6-pyrazine, bppz=2.3-di-2-pyridylpyrazine), were designed and synthesized. The structure of [(ppy)₂Irppz]Cl was determined by single crystal X-ray diffraction. Their photophysical properties were also studied. This kind of complexes could coordinate with Cu²⁺, the photoluminescence (PL) of the complex was quenched, and the color changed from orange-red to green. The forming M-Cu (M: complexes 1 and 2) ensemble could be further utilized as a colorimetric and emission "turn-on" bifunctional detection for CN^-, especially for complex 1-Cu²⁺ showed a high sensitivity toward CN^- with a limit of diction is 97nM. Importantly, this kind of iridium(III) complexes shows a unique recognition of cyanide ions over other anions which makes it an eligible sensing probe for cyanide ions.