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

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