Generation of long-lived methylviologen radical cation in the triplet-state mediated electron transfer in a β-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 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)–Pyradical dot+–MVradical dot+. A second electron transfer then occurs from Ru(II)Py^.+-MV^.+ 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^.+.