Dimethoxyphenoxy alpha-substituted metal-free, and metal phthalocyanines: Electrochemical redox, in-situ spectroelectrochemical and electrochromic properties

In this study, (2,3-dimethoxy)phenoxy alpha-substituted CoPc (2) and CuPc (3) complexes were newly synthesized and spectrally characterized. The electrochemical, in situ spectroelectrochemical, and electrochromic properties of CoPc (2), CuPc (3), ZnPc (4), and H₂Pc (5) were also investigated. This investigation discussed the electron-releasing effect of the methoxy (-OCH₃) groups on the outermost part of the molecule compared with a previously reported (2,6-dimethoxy)phenoxy cobalt phthalocyanine. The results revealed that changing the binding positions of the substituting groups of the phthalocyanines led to detectable changes in the redox properties of complexes. The CoPc (2) showed additional redox processes and in situ spectroelectrochemical changes under potential during these processes compared to other complexes due to the redox-active nature of the metal center. Thus, the electrochromic features of the films of these complexes on indium-tin-oxide (ITO) electrodes were also identified and discussed. The films of the complexes displayed promising electrochromic responses with reversible redox processes, fast coloration, and high optical stability. ITO/CoPc (2) had the best electrochromic properties among these phthalocyanine films thanks to its rich redox nature.