Luminescent Cyclometalated <i>N</i>-Heterocyclic Carbene-Containing Organogold(III) Complexes: Synthesis, Characterization, Electrochemistry, and Photophysical Studies

A new class of luminescent mononuclear and dinuclear N-heterocyclic carbene-containing gold(III) complexes has been synthesized and characterized. The X-ray crystal structures of most of the complexes have also been determined. Electrochemical studies reveal a ligand-centered reduction originated from the RC∧N∧CR moieties with no oxidation waves. Interestingly, one of the dinuclear complexes exhibited two distinct reduction couples instead of one with the first reduction occurring at less cathodic potential, probably related to the splitting of the π* orbital-based LUMO resulting from intramolecular π−π interaction. The electronic absorption and luminescence behaviors of the complexes have also been investigated. In dichloromethane solution at room temperature, the low-energy absorption bands are assigned as the intraligand π−π* transition, with mixing of a charge transfer character from the aryl ring to the pyridine moiety of the cyclometalating RC∧N∧CR ligand. The low-energy emission bands are ascribed to origins mainly derived from the intraligand π−π* states with an aryl to pyridine charge transfer character of the cyclometalating RC∧N∧CR ligand.本研究合成并表征了一类新型发光单核及双核含氮杂环卡宾金(III)配合物。多数该类配合物的X射线晶体结构已被解析确定。电化学研究结果显示，其存在源于RC∧N∧CR基团的配体中心还原过程，且未观测到氧化波。值得关注的是，其中一款双核配合物展现出两组独立的还原偶，而非单一组还原峰，其首次还原的阴极电势更正，这一现象大概率与分子内π-π相互作用导致的π*轨道基最低未占据分子轨道（Lowest Unoccupied Molecular Orbital, LUMO）发生分裂相关。本研究同时对该类配合物的电子吸收与发光行为展开了探究。在室温下的二氯甲烷溶液中，低能吸收带被归因为配体内π-π*跃迁，且伴随环金属化RC∧N∧CR配体中芳环向吡啶基团的电荷转移特性。低能发射带则主要源自环金属化RC∧N∧CR配体的配体内π-π*态，同时带有芳环向吡啶的电荷转移特性。