Generation of long-lived methylviologen radical cation in the triplet-state mediated electron transfer in a beta-cyclodextrin based supramolecular triad

Abstract

A novel tris(bipyridyl) ruthenium-pyrene-methylviologen supramolecular triad was assembled through inclusion complexation of adamantane-linked Ru(II)-Py dyad in MV2+-linked beta-cyclodextrin. Excitation of the Ru(II) chromophore populated its (MLCT)-M-3 which upon energy transfer gave Py-3, which donates an electron to MV2+ to give Ru(II)-Py center dot+-MV center dot+. A second electron transfer then occurs from Ru(II) to Py center dot+ to give the supramolecular Ru(III)-Py-MV center dot+ charge separated state. Laser flash photolysis experiments confirmed formation of MV center dot+ which exhibited 100 mu s lifetime. Steady state irradiation of the self-assembled system in the presence of sacrificial donor also led to formation of long-lived MV.