Molecular aggregation in soluble phthalocyanines – Chemical interactions vs. π-stacking

Aggregation of soluble sulfonated phthalocyanines (Pcs) containing di- and trivalent central atoms in binary water-alcohol solvents has been studied. The equilibrium constants of dimerization in solutions of Pcs with divalent central atoms (Zn, Cu) were found dependent on the electrical permittivity of the solvent and on the degree of sulfonation (i.e., on the charge on the phthalocyanine anions). Our results show that in Pcs with the trivalent central atom (Al(OH)) the dimerization occurs preferentially by formation of oxygen bridges or hydrogen bonds. Disulfonated aluminum phthalocyanine anions dissolved in water-rich binary solvents seem to form both π-stacked dimers and chemical dimers, due to a decrease in the Coulombic repulsive energy. The experiments reported in the paper indicate that the aggregation of soluble phthalocyanines can be controlled by the choice of a suitable electric permittivity of the solvent.

► Dimerization of soluble sulfonated phthalocyanines (Pcs) was studied.
► Pcs with divalent central atoms form π-stacked dimers.
► Their dimerization constants depend on electric permittivities of solvents.
► Pcs with trivalent atoms preferentially form chemically bound dimers.
► Their dimerization constants weakly depend on the electric permittivities.