Chromonic-Like Physical Luminescent Gels Formed by Ionic Octahedral Iridium(III) Complexes in Diluted Water Solutions

The first example of spontaneous self-assembly of ionic octahedral Ir(III) complexes containing carboxylates counterions into luminescent ordered aqueous gel phases is reported. The gel phases formed at 2.5% w/w (Ir-C-i:H(2)0) are investigated by POM, H-1 and H-2 NMR and UV-vis spectroscopies, whereas a detailed structural analysis by WAXS, SAXS, and SANS experiments is performed for the acetate complex, in both anisotropic gel and isotropic phases. This comprehensive investigation shows that the complex with the shortest carboxylate self-assembles into double string polyelectrolyte-type supramolecular columns surrounded by the counterions, at low concentrations in the isotropic solution (1.0% w/w). Upon increasing concentration, these supramolecular columns grow one-dimensionally, and eventually gelation occurs and birefringent textures begin to be observed by POM, resembling the textures developed by chromonic systems. The gelation occurs with the close packing of the supramolecular columns sheathed in their solvation shell into a 2D rectangular lattice. Furthermore, a significant enhancement of the luminescence quantum yield is observed for all the complexes in the gel phases with respect to the isolated molecule.