Structure-switching M3L2 Ir(III) coordination cageswith photo-isomerising azo-aromatic linkers

摘要

Cyclotriguaiacylene has been functionalised with 3- or 4-pyridyl-azo-phenyl groups to form a series ofmolecular hosts with three azobenzene-type groups that exhibit reversible photo-isomerisation.Reaction of the host molecules with [Ir(C^N)2(NCMe)2]+ where C^N is the cyclometallating 2-phenylpyridinato, 2-(4-methylphenyl)pyridinato or 2-(4,5,6-trifluorophenyl)pyridinato results in the selfassembly of a family of five different [{Ir(C^N)2}3(L)2]3+ coordination cages. Photo-irradiation of each ofthe cages with a high energy laser results in E / Z photo-isomerisation of the pyridyl-azo-phenylgroups with up to 40% of groups isomerising. Isomerisation can be reversed by exposure to blue light.Thus, the cages show reversible structure-switching while maintaining their compositional integrity. Thisrepresents the largest photo-induced structural change yet reported for a structurally-integralcomponent of a coordination cage. Energy minimised molecular models indicate a switched cage hasa smaller internal space than the initial all-E isomer. The [Ir(C^N)2(NCMe)2]+ cages are weakly emissive,each with a deep blue luminescence at ca. 450 nm.