Introduction of a Disulfide Bond As a Key Element of Acyclic Bis-Thiourea-Type Anion Receptors

This article shows that a difference in the building blocks of the molecular framework, C-C to S-S, results in a significant influence on its optical properties. Acyclic anion receptors, bis[2[3-(substituted)thioureido]ethyl} disulfides were newly synthesized, and their optical properties in response to complex formation with an acetate ion were compared with those of a hexamethylene framework between two thioureido groups. Quantum chemical calculations suggested that receptors fold their molecular framework around disulfide because of the presence of the intramolecular hydrogen bonding between two N,N'-disubstituted thioureas. The complex of the receptor and the acetate ion with 1:1 stoichiometry consists of the coordination of two thioureido groups to the acetate via hydrogen bonds. This complex formation is accompanied by a dissociation of intramolecular hydrogen bonding and rotation of one side of the thioureido group. These circumstances of conformational changes in the molecular framework functioned by switching on and off the excimer fluorescence of the 1-pyrenylmethyl derivative.