Synthesis of Penta‐ and Tetrasubstituted Quercetins and Their Fluorescent Properties

Quercetin contains five hydroxy groups (OH) at positions 3, 5, 7, 3′, and 4′. The selective reaction of a hydroxy group in quercetin is an important strategy for the modulation of various properties of the derivatives. Herein, we report the synthesis of selective quercetin derivatives, wherein the oligoether chains were linked to the hydroxyl groups. Interestingly, the penta‐substituted quercetin derivative exhibited a higher fluorescence intensity than the tetra‐substituted one. The fluorescence behavior of synthetic derivatives was investigated using solvatochromism, molecular aggregations, computational calculations, and hydrogen bonds with solvents. The fluorescent penta‐substituted quercetin derivative did not show any cytotoxicity up to 600 μM concentration, showing a novel biocompatible fluorescent molecule.