Synthesis and mesogenic properties of β-tetrabrominated tetraalkyloxyporphyrins

A new class of 2,3,7,8-tetrabromo-5,10,15,20-tetrakis(4'-n-1-alkyloxyphenyl)porphyrins, H2T(4'-OCnP)PBr4 (n = 4,6,8,10,12,14,16 and 18) and their Cu(II) complexes have been synthesized regioselectively and their mesophase properties explored. The mesogenic properties of the porphyrins were examined by differential scanning calorimetry and optical microscopy. An increase in alkyl chain length of the mesogens, showed an increase in melting point temperature and lowering of their clearing point temperatures with the narrower mesophases. This has been ascribed to the decreased π-π interactions as evidenced from the crystal structure of H2T(4'-OC6P)PBr4·THF derivative. MT(4'-OCnP)PBr4 derivatives showed rectangular mesophases in contrast to discotic lamellar mesophases reported for the planar MT(4'-OCnP)P mesogens.