Metallo-phthalocyanines Containing 1,3,4-oxadiazole Substituents: Synthesis, Characterization, Electrochemical and Spectroelectrochemical Properties

The 4-[5-(undecylthio)-1,3,4-oxadiazol-2-yl)phenol (3)and 4-(4-(5-(undecylthio)-1,3,4-oxadiazol-2-yl)phenoxy)phthalonitrile (5)were prepared viasubstitution reactions. Metallo-phthalocyanines (6-9) were obtained by the cyclotetramerization of the phthalonitrile (5). The structures of novel compounds were verified using IR, H-1-NMR, mass, UV-Vis methods. Electrochemical characterization of synthesized MPcs (6-9)was carried out by the CV and SWV techniques in DCM/TBAP electrolyte. While MnClPc and CoPc complexes exhibited metal-based and ring-based reduction redox couples, CuPc and NiPc gave two ring-based reduction redox couples. Spectroelectrochemical measurements were performed to observe the color transition during the reduction and oxidation reactions. Thus, the potentials of using the complexes as electrochromic materials were investigated. The CoPc gave the Q band at 667 nm with a shoulder at 663 nm. When the potential was applied to the cell, the intensity of Q band decreased with a shift in wavelength (from 667 nm to 663 nm). In addition, the natural turquoise color (x=0.2720, y=0.3366) of CoPc turned to greenish blue color (x=0.3080, y=0.3461). During the oxidation reactions, CuPc and NiPc gave ring-based oxidation species. The intensity of Q bands decreased without shift. As a result of the in-situ spectroelectrochemical measurements, it was observed that CuPc and NiPc, have sharper color transitions and have the potential to be used as electrochromic materials.