A structural parameter to link molecular geometry to macroscopic orientation in discotic liquid crystals: study of metalloporphyrin tapes

Abstract

Novel liquid crystalline (LC) molecules were prepared from a dimeric porphyrin tape. A series of metal complexes (1_Zn, 1_Pd, 1_Cu, and 1_Ni) and the free-base form (1_2H) of the porphyrin tape formed a columnar LC phase. Although only the central metal ions were different among these compounds, 1_Ni, 1_2H, and 1_Cu aligned homeotropically in a sandwiched glass cell, while 1_Zn and 1_Pd exhibited a random orientation at a macroscopic scale. The strength of the π–π interactions, tunable by the distortion of the porphyrin cores through metallation, is a key factor for the observed macroscopic orientation difference.