Photoinduced electron transfer from [Ru(bpy)3]2+ to a calix[6]arene-encapsulated viologen electron acceptor

We have investigated the luminescence quenching of [Ru(bpy)3]2+ by dioctylviologen, either free or complexed by a calix[6]arene host, in dichloromethane solution at room temperature. The aim of this work is to assess the effect of complexation by the calixarene host on the ability of dioctylviologen to accept electrons from a reductant species in homogeneous solution. Our results show that electron-transfer quenching of the 3MLCT state of [Ru(bpy)3]2+ by free dioctylviologen in CH2Cl2 is diffusion controlled (kq = 1.42 1010 M1 s1). The inclusion of the latter within the calixarene macrocycle slows down the electron-transfer process by four times, as a consequence of the shielding of the quencher from the photoexcited electron donor and/or a smaller driving force for the electron transfer determined by the diminished electron-accepting power of dioctylviologen inside the calixarene.