Stimuli-Responsive Multifunctional Iridium(III) Complex Exhibiting Thermo-, Vapochromism, and Double Catalytic Activity

Multifunctional compounds with properties that may be triggered by different external stimuli are highly desirable yet challenging in their design and synthesis. Herein, we report a cyclometalated iridium(III) complex based on bulky 1,2-diphenylphenanthroimidazole (C^N) that can easily change its molecular geometry from trigonal-bipyramidal to octahedral or from a monomeric to dimeric state in response to external stimuli (temperature and solvent variations). The extensive characterization including variable-temperature ¹H NMR, single-crystal and powder X-ray diffraction corroborated by density functional theory calculations strongly indicates that the thermochromic behavior of the complex is attributed to the dimer–monomer transformations both in solution and in the solid state. The five-coordinated monomer instantaneously reacts with coordinating solvents (L = CH₃CN, CH₃OH, pyridine) affording octahedral complexes [Ir(C^N)₂(L)Cl]. Binding constants for the formation of the complexes with acetonitrile and methanol were estimated by UV–vis titration. Enabled by the ability to switch between the alternative structural states depending on the medium, the monomer exhibits an unprecedented combination of properties, including a reversible vapochromic behavior and switchable catalytic activity. As illustrative examples, transfer hydrogenation and photoinduced reductive debromination were successfully performed by using the monomer as a catalyst.