Fluorescent lanthanide complexes of Schiff base ligands possessing N-aryl moiety: influence of chain length on crossover (calamitic to discotic) phase behaviour

Abstract

New lanthanide complexes, Tb(III), Dy(III) and Gd(III) of N-aryl based Schiff bases exhibiting mesomorphism have been synthesised and characterised. The crossover phenomena of calamitic lamellar to discotic columnar phase behaviour in these lanthanidomesogens is found to be controlled by the variation in chain length of the single alkyl substituent on the terminal N-aryl ring, hitherto the first case of a metallomesogen with only one alkyl chain length at each end of the ligand as evidenced by thermal microscopy studies and complemented by X-ray studies. It is also observed as a function of temperature in a single component. The electronic properties of these systems are dominated by the donor–acceptor substituted organic chromophore ligand, and the emission maxima revealed a large Stokes shift of 160 nm. The ligand–ligand charge transfer is reflected in emission spectra and is due to the presence of phenyl rings in the ligands.

Keywords:

• lanthanide complexes
• lanthanidomesogen
• Schiff bases
• crossover phase behaviour
• metallomesogens
• liquid crystal

Acknowledgements

Financial assistance is provided by DST, DAE, DRDO and UGC India, International Institute for Complex Adaptive Matter (I2CAM). We are thankful to Professor N.A. Clark and Dr C. Jones for providing X-ray experimental facilities.