Cholesterol appended pyridinium ureas: a case of gel making and breaking for selective visual readout of F−

Abstract

Cholesterol appended pyridinium ureas 1 and 2 have been designed and synthesized. The unsymmetrical urea-based chemosensor 1 fluorimetrically distinguishes F⁻ from the other anions examined in both CH₃CN and DMSO with appreciable binding constant values. The pyridinium – based symmetrical compound 2 acts as a low molecular weight gelator (LMWG) in CHCl₃ and is capable of detecting F⁻ visually by breaking the gel. On the contrary, the chemosensor 1 in DMSO in the presence of tetrabutylammonium fluoride undergoes a change from sol to gel state that produces an unambiguous visual readout of F⁻.