Discotic liquid crystals of transition metal complexes, 31: establishment of mesomorphism and thermochromism of bis[1,2-bis(4-n-alkoxyphenyl)ethane-1,2-dithiolene]nickel complexes

Two series of bis[1,2-bis(4-n-alkylphenyl)ethane-1,2-dithiolene]nickel, Cn–Ni (n = 1–12), and bis[1,2-bis(4-n-alkoxyphenyl)ethane-1,2-dithiolene]nickel, CnO–Ni(n = 1–12, 14, 16, 18), have been synthesized. Their mesomorphism, thermochromism, supramolecular structures and π-acceptor property have been investigated by using different scanning calorimetry, polarizing microscopy, temperature-dependent X-ray diffraction technique, electronic spectroscopy and cyclic voltammetry. From the X-ray diffraction and electronic spectral results, it was established that the CnO–Ni complexes for n≤10 exhibit two differently colored discotic lamellar (DL) mesophases whereas none of the Cn–Ni complexes has a mesophase, and that the thermochromism (brown → green) is attributable to a slow transformation from the Ni–Ni bonded dimers to the Ni–S bonded dimers.