Optical properties of red/near infrared light-harvesting supramolecular porphyrin synthesized via electrochemical polymerization of pyrrole – Effect of aging, Ca-metallation and H2O2 interaction

Abstract

Sustainable green hydrogen production (SGHP) is one of the alternative solutions to the depletion of fossil fuel resources and associated carbon emissions. To achieve SGHP, solar energy absorbing and converting catalysts are currently being exploited. Among these catalysts, supramolecular porphyrins remain very attractive due to their biocompatibility, ability to store protons, structural tunability as well as electron exchange characteristics. However, they are limited by high-energy syntheses and purification or transformation involving toxic chemicals. This work represents the first report on the production of a red/near infrared-absorbing porphyrin through the condensation of an electrolyzed pyrrole solution with an aldehyde at room temperature. The oxidation process was followed by monitoring the change in the pH during the cycling of the pyrrole solution. The ultraviolet–visible spectrophotometric screening was used at the end of each cycle to determine the change in the absorption characteristics of the solution. Photoluminescence and proton NMR studies further confirmed the production of the targeted free base porphyrin. The presence of the unprotonated and protonated core nitrogen atoms of the porphyrin was confirmed by interaction with H2O2, KF and Ca2+ ion. The process required no reflux or purification via the use of toxic organic solvent.