Abstract
Cationic Zn(II) tetraalkyltetrapyridinoporphyrazinium derivatives bearing N-alkyl chains of different length (ZnPc 2 R:-CH3, ZnPc 3 R:-(CH2)11CH3, ZnPc 4, R:-(CH2)15CH3) were synthesized from Zn(II) tetrapyridinoporphyrazine (ZnPc 1). The cyclotetramerization of 3,4-pyridinedicarbonitrile with zinc(II) acetate in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) produces ZnPc 1 as mixtures of constitutional isomers with 67 % yield. The exhaustive alkylation of ZnPc 1 gives ZnPc 2, ZnPc 3 and ZnPc 4 with 95, 91 and 90 % yields, respectively. Absorption and fluorescence spectroscopic studies of these sensitizers were analyzed in reverse micelle of n-heptane/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water varying the amount of water dispersed in the reverse micelles (W0 =[H2O]/[AOT]). Under these conditions, solubilization of ZnPc 2-4 take places at W0>30. Also, the spectra were analyzed at different AOT concentration keeping W0=30 constant. These results were used to determine the binding constant (Kb) between these sensitizers and AOT reverse micelles. The values of Kb of 283, 150 and 34 were found for ZnPc 2, 3 and 4, respectively. The photodynamic activity was evaluated in AOT system using 9,10-dimethylanthracene (DMA). The photooxidation rate of DMA sensitized by these phthalocyanines follow the order: ZnPc 2 > ZnPc 3 ~ ZnPc 4. Therefore the studies show that in AOT reverse micelles, the cationic ZnPc 2 is an efficient photosensitizer with potential applications in photodynamic therapy.
Highlights
Phthalocyanines derivatives exhibit a high absorption coefficient (ε>105 M-1cm-1) in the visible region of the spectrum, mainly in the phototherapeutic window (600-800 nm) and a long lifetime of triplet excited state to produce efficiently O2(1∆g) [1]
Where [zinc phthalocyanines (ZnPcs)]0 is the total concentration of the porphyrin, A is the absorbance at different [AOT], AHp is the absorbance in n-heptane, εb and εHp are the molar absorptivity for the phthalocyanine bound to the interface and in the organic medium, respectively
Tetracationic ZnPc 2-4 were conveniently synthesized by alkylation of ZnPc 1, which was obtained from the condensation of phthalonitrile derivative in presence of DBU and Zn(II) acetate
Summary
Phthalocyanines derivatives exhibit a high absorption coefficient (ε>105 M-1cm-1) in the visible region of the spectrum, mainly in the phototherapeutic window (600-800 nm) and a long lifetime of triplet excited state to produce efficiently O2(1∆g) [1]. The absorption spectra of ZnPc 2-4 were analyzed in n-heptane/AOT M) varying the amount of water dispersed in the reverse micelles (W0 = [H2O]/[AOT]). ZnPc 2 is not soluble in AOT system at low W0.
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