Structure-switching M3L2 Ir(iii) coordination cages with photo-isomerising azo-aromatic linkers (Data accessibility: data are available at https://doi.org/10.5518/438)

• Published in: Chemical science (Cambridge) 2018-11, Vol.9 (42), p.8150-8159
• Main Authors: Oldknow, Samuel, Diego Rota Martir, Pritchard, Victoria E, Blitz, Mark A, Fishwick, Colin W G, Zysman-Colman, Eli, Hardie, Michaele J
• Format: Article
• Language: English
• Subjects: Azo compounds; Cages; Crystallography; Isomerization; Self-assembly; Switching
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c8sc03499k

Cyclotriguaiacylene has been functionalised with 3- or 4-pyridyl-azo-phenyl groups to form a series of molecular 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 self-assembly of a family of five different [{Ir(C^N)2}3(L)2]3+ coordination cages. Photo-irradiation of each of the cages with a high energy laser results in E → Z photo-isomerisation of the pyridyl-azo-phenyl groups 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. This represents the largest photo-induced structural change yet reported for a structurally-integral component of a coordination cage. Energy minimised molecular models indicate a switched cage has a 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.