Tris(5-aryl-1,3,4-oxadiazolyl)benzotrithiophenes : discotic liquid crystals with enormous mesophase ranges

Abstract

C3-symmetrical, alkoxyphenyl substituted 2,5,8-(tris-1,3,4-oxadiazol-2-yl)benzo [1,2-b; 3,4-b′; 5,6-b′′]trithiophenes (OXD-BTT) are synthesized via threefold Huisgen-reaction. A broad variation of alkoxy substitution pattern and chain lengths is reported. The thermal behavior was investigated via differential scanning calorimetry (DSC), polarized optical microscopy (POM) and thermogravimetry (TGA). Optical properties were studied via UV-Vis and fluorescence spectroscopy. Structural information of the LC phases was gained from X-ray diffraction on oriented fibers. OXD-BTT provide enormous phase widths (ΔT≥289 K) with clearing points close to thermal decomposition. Most of the derivatives exhibit two different mesophases, the lower phase with a rectangular 3D-structure and a hexagonal 2D-lattice at higher temperature. The variation of the chain length allows a tuning of melting and clearing points. OXD-BTT emit blue light with fluorescence quantum yields up to 30 % in good solvents. The emission is very sensitive to aggregation, thus, in poor solvents the emission intensity decreases, and red shift of maxima occurs.