Columnar discotic Pt(ii) metallomesogens as luminescence multifunctional materials with chemo and thermosensor abilities

Abstract

A new family of Pt(II) luminescent metallomesogens based on dicatenar pyridylpyrazolate ligands [Pt(pz^R(n,n)py)₂] (R(n,n) = C₆H₃(OC_nH_2n+1)₂, n = 4–18) has been prepared, and their mesomorphic and photophysical properties are described. The compounds were isolated as red (n = 4–8) or yellow (n = 10–18) solids at room temperature, but the first ones were converted to yellow crystals by slow evaporation of a chloroform–acetone mixed solution. All of them behave as discotic liquid crystal materials, exhibiting hexagonal columnar mesophases (Col_h) in a wide range of temperatures. Photoluminescence studies in the solid state at variable temperatures showed a high emission in the liquid crystalline phase, which was significantly red-shifted with respect to the yellow-green emission of the solid state. This photophysical change was attributed to the formation of aggregates through Pt(d_z²)–Pt(d_z²) interactions, thereby giving rise to the metal–metal-to-ligand charge transfers (³MMLCT) responsible for the luminescence observed. Taking advantage of these properties we have fabricated polymeric solid supports doped with the platinum complex [Pt(pz^R(10,10)py)₂], which can be used as temperature sensors for real technological applications. In addition, the Pt–bispyrazolate complexes and their corresponding pyrazole ligands have been proved to be useful as chemosensors towards Pd²⁺, Zn²⁺, Cd²⁺ and Hg²⁺ metal ions.