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

• We examine the luminescence quenching of [Ru(bpy)3]2+ by free and complexed dioctylviologen.
• Dioctylviologen quenches the excited Ru complex by electron transfer.
• Quenching by free dioctylviologen occurs with a diffusion-controlled rate.
• Inclusion of dioctylviologen in a calixarene slows down the electron-transfer process by four times.
• The results highlight a shielding of the quencher exerted by the calixarene host.

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 M−1 s−1). 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.

The inclusion of dioctylviologen into a calix[6]arene host slows down the electron-transfer process from photoexcited tris(bipyridine)ruthenium(II) by more than four times in comparison with free dioctylviologen in dichloromethane solution.Figure optionsDownload as PowerPoint slide