Monomerization and photodynamic activity of Zn(II) tetraalkyltetrapyridinoporphyrazinium derivatives in AOT reverse micelles

Monomerization and photodynamic activity of cationic Zn(II) tetraalkyltetrapyridinoporphyrazinium derivatives bearing N-alkyl chains of different length (ZnPc 1 R: –CH3, ZnPc 2 R: –(CH2)11CH3, ZnPc 3, R: –(CH2)15CH3) were evaluated in n-heptane/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water micellar system. Absorption and fluorescence spectroscopic studies of these sensitizers were analyzed in n-heptane/AOT (0.1 M)/water system by varying the amount of water dispersed in the reverse micelles (W0 = [H2O]/[AOT]). Under these conditions, the absorbance of the monomeric Q-band (∼686 nm) of ZnPcs 1–3 increases rapidly until W0 ∼ 30 and then the increase becomes steady. These results were also confirmed by fluorescence studies. Analysis of the Q-band at different AOT concentrations, keeping W0 = 30 as constant, was carried out to determine the binding constant (Kb) between these sensitizers and AOT reverse micelles. The values of K of 210, 150 and 34 were found for ZnPcs 1, 2 and 3, respectively. Photodynamic activity of these sensitizers was evaluated in AOT system using 9,10-dimethylanthracene (DMA). The photooxidation rate of DMA sensitized by these phthalocyanines follow the order: ZnPc 1 > ZnPc 2 ∼ ZnPc 3. As shown by spectroscopic and photodynamic studies, the AOT reverse micellar system very effectively inhibits the aggregation of phthalocyanines, promoting the formation of photoactive monomeric species.