Synthesis and properties of 5,10,15,20-tetra[(4-alkoxy-3-ethyloxy)phenyl]porphyrin hydroxylanthanide liquid crystal complexes

Twelve 5, 10, 15, 20-tetra(4-alkoxy-3-ethyloxy)phenyl]porphyrin hydroxylanthanide complexes Ln(C_nOEOP)₄P](OH) (n = 12, 14, 16;Ln = Tb, Dy, Er, Yb) and three ligands have been synthesized and their composition, structure and spectral properties studied. Their liquid crystalline behaviour is also presented. Differential scanning calorimetry and polarizing optical microscopy reveal that all exhibit a discotic liquid crystalline phase. X-ray diffraction shows that the mesophase is a hexagonal columnar, Col_h. The lanthanide ion, which is coordinated to the four nitrogen atoms of the porphyrin and to the oxygen atom of the hydroxyl group, is out of the porphyrin molecular plane. All the complexes are stable below 200°C and undergo complete decomposition at 800°C. The fluorescence quantum yields of the lanthanide complexes are much lower than those of the corresponding ligands. The electrochemical studies show that the redox potentials do not change on varying the chain length.