New cationic zinc azaphthalocyanines (AzaPc) were prepared using a statistical method of synthesis starting from 5,6-bis(2-diethylaminoethylsulfanyl)pyrazine-2,3-dicarbonitrile (A) and 5,6-bis(tert-butylsulfanyl)pyrazine-2,3-dicarbonitrile (B). All the six possible AzaPc derivatives were detected on TLC but only five of them were finally isolated using column chromatography on silica (excluding AAAB type). The adjacent (AABB) and opposite (ABAB) isomers were well separated. Singlet oxygen quantum yields (ΦΔ) were measured using the DPBF decomposition method.
Values of ΦΔ in anhydrous dimethylformamide (DMF) drastically decrease with the number of amino groups from 0.66 for BBBB type to 0.04 for AAAA type. The same dependence was observed in anhydrous DMF for the corresponding hydrochlorides. When DMF/water 95:5 added with HCl was used, the ΦΔ values for amino AzaPc increased to approximately 0.66. This suggests that solvation of the amino and Cl− ions plays an important role in the separation of the AzaPc molecules although no changes were found in UV–vis spectra.
At least eight cationic charges are necessary for complete monomerization of AzaPc in water. Fewer charges lead to significant decrease of the absorption in the area of the Q-band and to pronounced dimeric character of the absorption spectrum.
Zimcik, P., Miletin, M., Musil, Z., Kopecky, K., Kubza, L. and Brault, D., 2006. Cationic azaphthalocyanines bearing aliphatic tertiary amino substituents—Synthesis, singlet oxygen production and spectroscopic studies. Journal of Photochemistry and Photobiology A: Chemistry, 183(1), pp.59-69.
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Categories: Material & Chemical