Reversible sol–gel transition of a tris–urea gelator that responds to chemical stimuli

Tris–urea 1 functioned as a low-molecular-weight gelator for a variety of polar organic solvents. An acetone gel of 1 became a homogeneous solution in response to the addition of anions. The minimum amount of anion necessary for the gel–sol transition was specific to the anion species. A linear relationship was demonstrated between the amount of anion required and the total binding constant of 1 with the anion. Re-gelation occurred by addition of BF3·OEt2 and with ultrasound irradiation of the acetone solution of 1 and F−.