Synthesis, Spectroscopic Properties and Photodynamic Activity of Zn(II) tetraalkyltetrapyridinoporphyrazinium Derivatives

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.