Red to Green Switch Driven by Order In a Ionic Ir(III) Liquid Crystalline Complex

New cationic IrIII materials of general formula [Ir(ppy) 2(Cn-bpy)]PF6 {H(ppy) = 2-phenylpyridine; Cn-bpy = 3,4,5-R-4,4′-benzoyloxymethyl-2,2′-bipyridine; n = 8, R = OC8H17; n = O, R = H} were synthesised and fully characterised. Both complexes show high phosphorescence quantum yields in their condensed phases. Moreover, the introduction of long alkoxy chains on the bipyridne ligand in [Ir(ppy)2(C8-bpy)]PF6 (1) has induced mesomorphism, and consequently a dynamic functional material with properties modulated by external stimuli has been obtained. Starting from the isotropic phase, on slow cooling a crystalline phase characterised by a bright green emission is obtained. However, on fast cooling a kinet-ically favoured columnar hexagonal mesophase is preferentially formed, which is stable down to room temperature. In this phase, the high luminescence is still maintained, even if a switch to yellow emission colour is observed, Moreover, through spin coating of solutions of 1, it has been possible to obtain its amorphous thin film to accomplish a further shift of the emission wavelength in the orange-red spectral range. A fully reversible colour tuning process by surface stress and heating from the orange-red film to the green crystalline phase, indicative of a mechanochromic behaviour, is also achieved. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.