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(OCnH2n+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(z)(2))-Pt(d(z)(2)) interactions, thereby giving rise to the metal-metal-to-ligand charge transfers ((MMLCT)-M-3) 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.