Discotic liquid crystals of transition metal complexes, part 36: syntheses and mesomorphic properties of very large discotic liquid crystals based on triphenylenocyanine and 1,4-diazatriphenylenocyanine

Abstract

Two series of very large discotic complexes of tetrakis (2,3,6,7-tetraalkoxy)triphenylenocyaninato copper(II) (abbreviated as ( C n O )16 TcCu ; n = 8, 10, 12 and 14) and tetrakis(2,3,6,7-tetraalkoxy)-1,4-diazatriphenylenocyaninato copper(II) (abbreviated as ( C n O )16 TzCu ; n = 8, 10, 12 and 14), were synthesized to investigate their mesomorphic properties by differential scanning calorimetry, thermogravimetry analysis, polarizing optical microscope observation and temperature-dependent X-ray studies. The results show that each of the ( C n O )16 TcCu derivatives exhibits two or three disordered rectangular columnar ( Col rd ) mesophases from room temperature to the decomposition temperature at ca. 330-340°C under nitrogen gas. However, each of the ( C n O )16 TzCu complexes exhibits only one ordered tetragonal columnar ( Col tet.o ) mesophase in an extremely wide temperature region from room temperature to the decomposition temperature at ca 300°C and ca. 340-350°C under the atmosphere and nitrogen gas, respectively. It is very interesting that the Col tet.o mesophase of ( C n O )16 TzCu for n = 10, 12 and 14 shows remarkable spontaneous homeotropic alignment in a large area, without disclinations and polydomains, in the temperature range from room temperature to the decomposition temperature. As far as we know, these discotic liquid crystals are the first examples to show homeotropic alignment at room temperature. Furthermore, the difference between the mesomorphic properties of ( C n O )16 TcCu and ( C n O )16 TzCu originated only from the additional eight nitrogen atoms in the central core in ( C n O )16 TzCu .