Electrochemically controllable reversible formation of cucurbit[8]uril-stabilized charge-transfer complex on surface

Abstract

The reversible formation of cucurbit[8]uril (CB[8])-stabilized charge-transfer (CT) complex on gold, which can be regulated by electrochemical stimuli, is reported. A viologen-based thread molecule with a thiol terminus was designed to synthesise a stable CB[8]-threaded [2]pseudorotaxane (5(2+)). A mixed self-assembled monolayer (SAM) of 5(2+) and 3-mercaptopropionic acid (3-MPA) on gold was prepared and characterised by reflectance FT-IR spectroscopy. The formation and disruption of a CT complex on surface was investigated by cyclic voltammetry with the SAM on gold as a working electrode in a supporting electrolyte solution containing 2,6-dihydroxynaphthalene (DHNp). The cathodic peak was shifted to a more negative potential (Delta E similar to 40mV) when compared with that measured without DHNp in the electrolyte, which confirmed the formation of a CT complex on gold upon immersion of the SAM of 5(2+) on gold in the supporting electrolyte containing DHNp. When the viologen unit was reduced, the CT complex was destroyed and the electron-rich guest molecule was released. Upon reoxidation of the reduced viologen unit, however, the CT complex was slowly reformed.