Selective Extraction, Recovery, and Sensing of Hydroquinone Mediated by a Supramolecular Pillar[5]quinone Quinhydrone Charge-Transfer Complex

Intermolecular interactions between an electron-rich aromatic hydroquinone (HQ) with its electron deficient counterpart, benzoquinone (BQ), result in the formation of a quinhydrone charge-transfer complex. Herein, we report a novel quinhydrone-type complex between pillar[5]­quinone (P[5]­Q) and HQ. Characterized by a suite of spectroscopic techniques including 1H NMR, UV–visible, and FTIR together with PXRD, SEM, BET, CV, and DFT modeling studies, the stability of the complex is determined to be due to an electron–proton transfer reaction coupled with a complementary donor–acceptor interaction. The selectivity of P[5]­Q toward HQ over other dihydroxybenzene isomers allows for not only the naked-eye detection of HQ but also its selective liquid–liquid extraction and recovery from aqueous media.