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Aggregation and disaggregation of anionic aluminum phthalocyanines in cationic pre-micelle and micelle media: A fluorescence study

2012; Elsevier BV; Volume: 235; Linguagem: Inglês

10.1016/j.jphotochem.2012.03.002

1873-2666

Raquel F. Correia, Suzana M. Andrade, Maria Isabel Viseu,

Photochemistry and Electron Transfer Studies

The interactions of two anionic aluminum phthalocyanines (Pcs), the tetrasulfonated (AlPcS4) and the monosulfonated (AlPcS1) species, with the cationic detergent n-dodecyltrimethylammonium chloride (DTAC) were investigated. These studies were performed by UV–visible absorption, steady-state and transient-state fluorescence, fluorescence lifetime imaging microscopy (FLIM), and fluorescence correlation spectroscopy (FCS). For both AlPcS4 and AlPcS1, large complexes of Pc–DTAC were formed at low surfactant concentrations, in the pre-micelle range. These complexes were visualized by the FLIM technique, directly in a drop of the sample. As the DTAC concentration increased, the size of the complexes decreased significantly. Above the detergent critical micelle concentration (CMC ≈ 22 mM), highly fluorescent monomers of both AlPcS4 and AlPcS1 were found to be strongly bound to the DTAC micelles surface: large equilibrium binding constants, Kb = 3.5 × 105 and 6.2 × 104, were obtained for AlPcS4 and AlPcS1, respectively. The aggregation/disaggregation behavior of phthalocyanines likely results from a delicate balance in the system, between hydrophobic attractions (Pc–Pc) and electrostatic attractions (anionic Pc macrocycles – cationic DTAC headgroups) and repulsions (between anionic sulfonated groups of Pc macrocycles).