Self-assembling properties of non-ionic tetraphenylporphyrins and discotic phthalocyanines carrying oligo(ethylene oxide) alkyl or alkoxy units

The thermotropic phase behaviour and self-assembling features of some non-ionic tetraphenylporphyrins and phthalocyanines containing oligo(ethylene oxide) alkoxy or alkyl units have been investigated. From DSC measurements and polarization microscopy it was concluded that none of the tetraphenylporphyrins was mesomorphic while the phthalocyanines displayed discotic hexagonal phases even at room temperature. The aggregation of the compounds in aqueous media was studied by means of UV-VIS and fluorescence spectroscopy and it has been found that in water the tetraphenylporphyrins form J- or head-to-tail type of aggregates while phthalocyanines form H- or face-to-face type of aggregates. The luminescence properties of the tetraphenylporphyrin and phthalocyanine aggregates are explained on the basis of the molecular exciton approximation. Steric constraints and orientational disorder in the tetraphenylporphyrin aggregates determine the luminescence yield relative to the monomeric species. The cofacial arrangement of the macrocycles in phthalocyanine aggregates results in a forbidden S-1-S-0 transition and thus in a complete disappearance of the luminescence.