New Insights into the Physicochemical and Electrochemical Characterization of Gold Phthalocyanine-Based Materials

Gold phthalocyanine-based materials can allow to combine the unique physical properties of the metallophthalocyanine with gold for numerous applications such as (photo)-electrochemistry or the so-called single atom catalysts (SACs), which require very small amounts of metal. However, there is currently a lack of physico-chemical and electrochemical knowledge to consider such applications. We report the synthesis and the physical characterization of three types of materials, the unsubstituted and the octo-substituted gold phthalocyanines AuPc, AuPc(CN)8 and AuPc(COOH)8, which were successfully synthesized. To interrogate the physicochemical and electrochemical properties of the as-synthesized materials, we have performed a multi-variant study by integrating different methods (UV-vis, FTIRS, TGA-TDA, HR-ESI-MS, SEM-EDX, XRD, XPS, CV). UV-vis confirms the shift towards high wavelengths (bathochromic effect) for the transition Q-band (charge transfer from pyrrolic carbons to neighboring atoms in the macrocycle) of AuPc(CN)8 and AuPc(COOH)8 compared to AuPc. CV in both aqueous and non-aqueous provides the first electrochemical insights into the phthalocyanine ring reduction and oxidation, AuPc/[AuPc]-, [AuPc]-/[AuPc]2- and [AuPc]2-/[AuPc]3-. The results delineate a possible rational pathway for AuPc-based materials or alternatively, their transformation into SACs, where a single Au atom is embedded in a nanostructured carbon-nitrogen scaffold.