| Abstract |
The interactions of two anionic aluminum phthalocyanines (Pcs), the tetrasulfonated (AlPcS4) and the monosulfonated (AIPcS(1)) 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 approximate to 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, K-b = 3.5 x 10(5) and 6.2 x 10(4), 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). (C) 2012 Elsevier B.V. All rights reserved. |
