Covalent bonding in perimidine-containing perinone systems: a case study using potentiodynamic oxidation of 14H-benzo[4,5]isoquino[2,1-a]perimidin-14-one

In recent years, we have focused our research on the oxidative addition/coupling of monomers from the perinone group, where the reaction occurs between perimidine segments. So far, we have used rather complex and difunctional isoidolo-[2,1-a]perimidinones and isoquino-[2,1-a]perimidinones, which resulted in solid products that were difficult to analyze. The primary objective of these studies was to propose simple, monofunctional perimidine monomers and evaluate their reactivity through the characterization of their soluble electrooxidation products. The reference compounds were structural analogues lacking perimidine, yet derived from the same anhydrides, i.e. 11H-isoindolo[2,1-a]benzimidazole-11-on (1,2-benzoylenebenzimidazole) (A1), and 7H-benzimidazo[2,1-a]benzo[de]isoquinolin-7-one (1,8-naphthoylene-1′,2′-benzimidazole) (A2). In this work we investigated the electrooxidation of 12H-isoindolo-[2,1-a]perimidin-12-one (12-phthaloperinone) (B1) and 14H-benzo[4,5]isoquinolino[2,1-a]perimidin-14-one (naphthaloperinone) (B2) to compare their oxidative reactivity and define the bis-perimidine bonding. While the A series did not form electroactive material after oxidation, the B series successfully formed the conductive layer, indicating that perimidine unit is capable of oxidative addition. However, the B2 electrocoupling process was characterized by the best efficiency. Mass spectrometry (MS), quantum chemical calculations, as well as UV–Vis-NIR and ESR spectroelectrochemistry analyses of the dissolved and solid electrooxidation products of B2 (i.e. 1pFr, 2pB2, respectively) revealed the presence of multiple products, including one-bonded deprotonated bis-perimidine dimers, especially in 1pFr fraction. We propose that specific intermolecular interactions more promote the suitable orientation of the singly-linked dimer and by its subsequent oxidation under alternating potential giving transition from the semi-ladder (1pB2) to the ladder structure presented by 2pB2. The conditions of the electrodynamic oxidation process determine the deprotonation and discharge of some dimers. However, in certain cases, the bonds remain protonated due to stabilization by hydrogen bonds, which arises from the proximity of the carbonyl group. The multiredox nature of the solid product 2pB2 is related to the presence of a mixture of different dimers: one- or two-bonded, and also protonated dimers. Our findings offer new insights into the mechanisms of perimidine bonding within group of perinone compunds, highlighting their potential for synthesising a novel class of organic compounds through electrochemical methods.