Micellization-controlled self-assembly of ZnPc(SO₂Cl)₄ in aqueous media: spectroscopic, dynamic light scattering, and...

The aggregation behavior of zinc tetrasulfonyl chloride phthalocyanine (ZnPc (SO ₂Cl) ₄) in aqueous media was investigated using UV-Visible spectroscopy, dynamic light scattering (DLS), and density functional theory (DFT) calculations. In DMF, ZnPc(SO₂Cl)₄ exhibits well-defined Q and Soret bands, indicating the presence of predominantly monomeric species. In contrast, increasing the water fraction promoted strong π-π stacking interactions between the macrocycles, leading to H-type aggregates characterized by Q-band broadening and hypochromism. The addition of sodium dodecyl sulfate (SDS) progressively disrupted these aggregates and modulated the supramolecular organization of the phthalocyanine. Spectral evolution combined with second-derivative analysis revealed an apparent micellization threshold at approximately 7.5 mM SDS, corresponding to the transition from aggregated species to surfactant-stabilized chromophores. DLS measurements supported this behavior, showing large aggregates in the premicellar regime (≈614 nm at 4 mM SDS), a significant reduction in hydrodynamic diameter near the critical micelle concentration (≈262 nm at 7.5 mM SDS), and the formation of ZnPc-SDS supramolecular assemblies in the post-micellar regime (≈398 nm at 9 mM SDS). DFT calculations further confirmed the favorable π-π stacking in ZnPc(SO₂Cl)₄ dimers and revealed increasing binding energies for ZnPc(SO₂Cl)₄-(SDS)ₙ complexes, highlighting the cooperative role of hydrophobic and electrostatic interactions in stabilizing the assemblies.