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

摘要

The supramolecular design of multicomponent systems that undergo photoinduced energy or electron transfer processes has been well recognized in view of its potential for development of nanosized molecular devices for solar energy conversion and components in photonic devices.The introduction of transition metals in such systems is attractive due to their high stability,tunable redox,and excited-state properties that can lead to the design of molecular wires,junctions,and transistors.The construction of multimetallic systems has been mostly based on the covalent linkage of the photoresponsive units.To overcome synthetic complexity and to access a library of dyads and triads,assembly based on cyclodextrin,CD,receptors has been used to form metal-containing donor-acceptor systems in water.We have recently reported that the direction of photoinduced energy transfer can be switched from or to a Ru(II) center appended to a cyclodextrin by the choice of the metalloguest,Os(II) or Ir(lII),bound in the CD cavity.To further advance the function of the assembly to vec-torially transfer energy in distinct steps,the selection of the direction of energy transport should be addressed by the spatial arrangement of the components.We report herein a self-assembled junction,formed by selective binding of three different photoactive components,in which a unidirectional two-step photoinduced energy transfer process takes place.