A Unidirectional Energy Transfer Cascade Process in a Ruthenium Junction Self-Assembled by α- and β-Cyclodextrins

A Ru(II) complex, Ru(2), with a trisbipyridyl core and two different receptor sites, - and -cyclodextrins, acts as a junction to recognize photoactive guests based on anthracene, Anth, and Os(II), Os-ada, in aqueous solution. Upon light excitation of the self-assembled system Anth·Ru(2)·Os-ada, an energy cascade process takes place from the Anth guest to the Ru(2) core, and subsequently, the energy is funneled to the Os-ada guest. The rates of the two photoinduced processes are determined by time-resolved emission and transient absorption spectroscopic techniques. The system introduces a directed self-assembly approach to unidirectional wires that can lead to nanosized arrays by judicious selection of the individual components.