A luminescent lyotropic liquid-crystalline gel of a water-soluble Ir(III) complex

Abstract

In the present study, the synthesis and properties of a novel water soluble Ir(III) complex of formula [(ppy)2Ir(dpq)]CH3CO2 is described, where ppy is the cyclometalated 2-phenylpyridine ligand and dpq the dipyrido[3,2-f:2′,3′-h]quinoxaline used as ancillary ligand. Own to its specific molecular structure, this complex forms highly ordered supramolecular gels in water on a wide range of concentration, from 3 to 14% w/w. The gel phase shows birefringence under cross polarisers that is completely loss when water is removed, evidence of the formation of a true lyotropic liquid-crystalline gel, without the need of an additional gelator. The gel is macroscopically formed of entangled microfibers that can be seen under optical microscope and that display luminescent properties as observed by confocal microscopy. X-Ray diffraction allowed to resolve the structure of the lyotropic mesophase that is formed by columns of complex cations organised in a tetrahedral manner which are in turn arranged in a larger oblique lattice, hence showing a high degree of order. The photophysical properties of the complex in its different state of matter (solid, gel phase and xerogel) are presented and discussed.