Supramolecular liquid crystalline dendrimers with a porphyrin core and functional carboxylic acid dendrons

Abstract

Novel liquid crystalline porphyrin dendrimers derived from 5,10,15,20-tetra-(4-pyridyl)porphyrins (TPyP) and their Zn complexes (ZnTPyP) have been synthesized by hydrogen bonding between the porphyrin core and four peripheral carboxylic acid dendrons derived from bis(hydroxymethyl)propionic acid (bis-MPA) to obtain 4 : 1 complexes. One family is derived from symmetric dendrons (G = 1 and 2) bearing promesogenic units in the terminal positions and two other families are derived from asymmetric dendrons (G = 1) that combine the promesogenic unit and an active moiety derived from coumarin or pyrene units. The formation of the complexes was confirmed by IR and NMR spectroscopy. The liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. Only porphyrin dendrimers (free base and Zn complexes) derived from symmetric dendrons exhibited a SmC mesophase. Porphyrin dendrimers derived from asymmetric dendrons did not show liquid crystalline behaviour. The UV-vis absorption and emission properties of the porphyrin dendrimers containing coumarin or pyrene have been investigated.