Regiospecific synthesis of tetrasubstituted phthalocyanines and their liquid crystalline order

Abstract

Metal-free and metal(II) all-endo-tetraalkoxy-phthalocyanines of C_4h symmetry are synthesised regiospecifically from 3-(2-butyloctyloxy)phthalonitrile with lithium octanolate and subsequent metal ion exchange. The voluminous, yet not overly large, and racemically disordered alkoxy substituent not only renders the cyclotetramerisation regiospecific, but also leads to liquid crystalline self-assembly with attainable clearing temperatures and persisting columnar organisation at room temperature. A rare hexagonal mesophase with twelve columns per hexagonal unit cell is found in the metal-free homologue, whereas the metal complexes show rectangular mesophases. The clearing temperature increases with increasing axial component of the metal ion coordination sphere. At low temperature, significant antiferromagnetic exchange between magnetic centres is observed for the Co^II homologue, whereas the magnetic centres are magnetically independent in the Cu^II derivative, in line with the observed higher clearing temperature in the Co^II case that testifies of stronger interdisk interactions.