Structurally Asymmetric Nonplanar π-Conjugated Naphthoquinone Derivatives Modified from Natural Lawsone for...

Aqueous organic redox flow batteries (AORFBs) have attracted growing interest for grid-scale energy storage by reducing reliance on scarce mineral resources used in transition metal-based systems. Natural naphthoquinone derivatives, while environmentally friendly and abundant, suffer from poor solubility and electrochemical instability, hindering their practical use in AORFBs. To address these challenges, we report the functionalization of a naturally abundant dye, lawsone (i.e., 2-HNQ), through non-planar π-conjugation extension and asymmetric intramolecular charge distribution, yielding a non-planar π-conjugated polar naphthoquinone derivative (namely BANQ) with enhanced water solubility and redox reversibility. Computational simulations and spectroscopic analysis confirmed that the introduction of benzoic acid group imparts a polar π-conjugation extended structure with asymmetric charge distribution. This structural modification efficiently enhances aqueous solubility and suppresses degradation pathways, such as Michael addition and irreversible keto-enol tautomerism. Compared with 2-HNQ precursor, BANQ exhibits lower sensitivity to nucleophilic and electrophilic attacks. The BANQ anolyte exhibited a very low-capacity decay rate of merely 0.00018% per cycle (or 0.045% per day), representing a two-order-of-magnitude reduction compared to that of 2-HNQ (0.032% per cycle or 8.22% per day). This study highlights the potential of modifying natural-derived products with rationally designed conjugated electron structure for green and sustainable energy storage solutions.