Cover Feature: 2-Sulfanylhydroquinone Dimer as a Switchable Fluorescent Dye (Chem. Eur. J. 62/2019) The monomesylated 2-sulfanyhydroquinone dimer emits blue light upon irradiation with UV light, whereas its photoluminescence activity turns off upon acylation of the phenolic hydroxyl group. 2-sulfanylhydroquinone dimer, acylation, biaryls, fluorescence, hydrolysis.