Turn-off fluorescence sensing of benzenediols <i>via</i> guest-induced π-conjugation switching in bisimidazole-based hydrindacene allosteric receptors

Fluorescent bisimidazole-based hydrindacene allosteric receptors 1a-c and 2 were synthesized for nonlinear ON/OFF sensing of benzenediols. By tuning their D-π-D conjugation through substituent modification, these receptors were designed to function as turn-off fluorescent sensors based on the cleavage of their π-conjugation accompanied by binding with benzenediols. The cooperative allosteric binding demonstrated selective and efficient nonlinear quenching toward orcinol.