On the nature of the electrode surface modification by cathodic reduction of tetraarylporphyrin diazonium salts in aqueous media

Different substrates have been modified through electroreduction of tetraarylporphyrin diazonium salts, H2TPP-N2+ or H2TPP-(N2+)4, generated in situ in acidic aqueous media from monoamino-TPP (H2TPP-NH2) or tetraamino-TPP (H2TPP-(NH2)4) in low concentration (5.10− 4 M). The modification of the electrodes with H2TPP-(NH2)4 leads to a purple deposit (PolyH2TPP-1) strongly linked to the electrode surface whereas those obtained from H2TPP-NH2 were not covalently linked to the electrode surface, soluble in organic solvents and identified as tetraphenylporphyrin (H2TPP). The deposits have been characterized by electrochemistry, atomic force microscopy (AFM) and UV–Visible absorption spectroscopy. Cyclic voltammetry of PolyH2TPP-1 revealed an electroactivity akin to that of polytetraarylporphyrin obtained by anodic electropolymerization of H2TPP (~ 2.10− 3 M) in strictly anhydrous electrolytic medium (PolyH2TPP-2). In light of their UV–vis spectra, the two related polymers present different intermolecular interactions and macromolecular organization.

► Tetraphenylporphyrin precipitates after reduction of the mono-aryldiazonium in H2O.
► Reduction of the tetra-aryldiazonium yields a deposit of poly-tetraphenylporphyrin.
► The polymer displays significant inter-porphyrin interactions (J-aggregation).