A series of nine luminescent iridium(III) complexes with pH-responsive imidazole and benzimidazole ligands have been prepared and characterized. The first series of complexes were of the form [Ir(ppy)₂(N^N)]⁺ or [Ir(ppy)₂(C^N)]⁺ (where ppy is 2-phenylpyridine and N^N is 2-(2-pyridyl)imidazole or 2-(2-pyridyl)benzimidazole and C^N represents a pyridyl-triazolylidene-based N-heterocyclic carbene ligand). For these complexes, the benzimidazole group was either unsubstituted or substituted with electron-withdrawing (Cl) or electron-donating (Me) groups. The second series of complexes were of the form [Ir(phbim)₂(N^N)]⁺ or [Ir(phbim)₂(C^N)]⁺ (where phbim is 2-phenylbenzimidazole and N^N is either 2,2′-bipyridine or 1,10-phenanthroline and C^N is either a pyridyl-imidazolylidene or pyridyl-triazolylidene N-heterocyclic carbene ligand). UV-visible and photoluminescence pH titration studies showed that changing the protonation state of these complexes results in significant changes in the photoluminescence emission properties. The pK_a values of prepared complexes were estimated from the spectroscopic pH titration data and these values show that the nature of the pH-sensitive ligands (either main or ancillary ligands) resulted in a significant capacity to modulate the pK_a values for these compounds with values ranging from 5.19–11.22. Theoretical investigations into the nature of the electronic transitions for the different protonation states of compounds were performed and the results were consistent with the experimental results.

中文翻译：

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唑类和N-杂环卡宾配体的pH响应性铱(III)配合物的实验和理论研究

一系列九种具有 pH 响应性咪唑和苯并咪唑配体的发光铱 ( III ) 配合物已被制备和表征。第一系列配合物的形式为 [Ir(ppy) ₂ (N^N)] ⁺或 [Ir(ppy) ₂ (C^N)] ⁺（其中 ppy 是 2-苯基吡啶，N^N 是 2- (2-吡啶基)咪唑或2-(2-吡啶基)苯并咪唑且C^N表示基于吡啶基-三唑基的N-杂环卡宾配体)。对于这些配合物，苯并咪唑基团要么未取代，要么被吸电子 (Cl) 或给电子 (Me) 基团取代。第二系列配合物的形式为 [Ir(phbim) ₂ (N^N)] ⁺或 [Ir(phbim) ₂ (C^N)] ⁺（其中 phbim 是 2-苯基苯并咪唑，N^N 是 2 ,2'-联吡啶或1,10-菲咯啉，C^N是吡啶基-咪唑基或吡啶基-三唑基N-杂环卡宾配体)。紫外可见光和光致发光 pH 滴定研究表明，改变这些配合物的质子化状态会导致光致发光发射特性发生显着变化。制备的配合物的pKa值是根据光谱 pH 滴定数据估算的，这些值表明 pH 敏感配体（主要配体或辅助配体）的性质导致调节这些配体的 pKa_值的显_着能力。化合物的值范围为 5.19–11.22。对化合物不同质子化态的电子跃迁性质进行了理论研究，结果与实验结果一致。