SELF-ASSEMBLING PROPERTIES OF NONIONIC 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(e thylene 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 d isplayed discotic hexagonal phases even at room temperature. The aggre gation of the compounds in aqueous media was studied by means of UV-VI S and fluorescence spectroscopy and it has been found that in water th e tetraphenylporphyrins form J- or head-to-tail type of aggregates whi le phthalocyanines form H- or face-to-face type of aggregates. The lum inescence properties of the tetraphenylporphyrin and phthalocyanine ag gregates are explained on the basis of the molecular exciton approxima tion. Steric constraints and orientational disorder in the tetraphenyl porphyrin aggregates determine the luminescence yield relative to the monomeric species. The cofacial arrangement of the macrocycles in phth alocyanine aggregates results in a forbidden S-1-S-0 transition and th us in a complete disappearance of the luminescence.