Enhancement of smectic C mesophase stability by using branched alkyl chains in the auxiliary ligands of luminescent Pt(II) and Pd(II) complexes

A novel series of Pd(II) and Pt(II) complexes based on cyclometallated imine ligands and N-benzoylthiourea (BTU) derivatives as auxiliary ligands has been prepared and their liquid crystalline properties as well as photophysical properties have been investigated. The crystal structure of one cyclometallated Pt(II) complex with N-(p-F-phenyl)-N′-benzoylthiourea as a co-ligand has been solved. The liquid crystalline properties have been investigated by a combination of DSC, POM and variable temperature powder X-ray diffraction. These new metallomesogens display either a monotropic SmC phase or both SmA and SmC phases, depending on the number of alkoxy groups attached to the imine ligand, alkyl chain length or the use of branched alkoxy terminal groups. We found that the introduction of branched alkoxy terminal groups lead to lower transition temperatures and stabilization of the SmC phase in both the Pd(II) and Pt(II) complexes. While the Pd(II) complexes display no emission, the Pt(II) complexes show good emission properties in solution, in the solid state and as a PMMA film at room temperature, and their investigation is reported.

Novel Pt(II) complexes based on cyclometallated imine ligands and N-benzoylthiourea (BTU) derivatives display smectic A and C phases as well as red emission.Figure optionsDownload as PowerPoint slide