Synthesis and electrochemical investigation of phthalocyanines with dendritic bulky ethereal substituents

Metal-free and metallophthalocyanines carrying four dendritic 3,4-bis(benzyloxy)benzyloxy groups on the periphery were prepared by cyclotetramerization of a new precursor, namely 4-[3,4-bis(benzyloxy)benzyloxy]phthalonitrile (2) in the presence of the corresponding divalent metal salts (Zn(II), Co(II)). The novel phthalonitrile derivative 2 was synthesized by the reaction of 4-nitrophthalonitrile and 3,4-dibenzyloxybenzyl alcohol (1), which was prepared by the catalytic reduction of 3,4-dibenzyloxybenzaldehyde with NaBH4 in ethanol. The new compounds were characterized by elemental analysis, together with FT-IR, 1H NMR and UV–Vis spectra. The electrochemical and in situ spectroelectrochemical measurements showed that while the cobalt phthalocyanine complex (5) gives both metal-based and ring-based redox processes, the metal-free and zinc phthalocyanine complexes (3 and 4) give only ring-based electron transfer processes. An in situ electrocolorimetric method was applied to investigate the colour of the electrogenerated anionic and cationic forms of the novel phthalocyanine complexes carrying bulky ethereal aryloxy substituents.

Novel phthalocyanines carrying four dendritic 3,4-bis(benzyloxy)benzyloxy groups on the periphery were prepared by cyclotetramerization of 4-[3,4-bis(benzyloxy)benzyloxy]phthalonitrile (2). The electrochemical and in situ spectroelectro-chemical measurements showed that while the cobalt phthalocyanine complex (5) gives both metal-based and ring-based redox processes, the metal-free and zinc phthalocyanine complexes (3 and 4) give only ring-based electron transfer processes. The in situ electrocolorimetric method was applied to investigate the colour of the electrogenerated anionic and cationic forms of the novel phthalocyanine complexes.Figure optionsDownload as PowerPoint slideHighlights
► Phthalocyanines with dendritic 3,4-bis(benzyloxy)benzyloxy groups were synthesized.
► Electrochemical and in situ spectroelectrochemical measurements were carried out.
► Cobalt phthalocyanine gives both metal-based and ring-based redox processes.
► Metal-free and zinc phthalocyanines give ring-based electron transfer processes.
► Electrocolorimetry was used to investigate the colour of the electrogenerated forms.