Photoinduced electron transfer in a triad that can be assembled/disassembled by two different external inputs. Toward molecular-level electrical extension cables

We have designed, synthesized, and investigated a self-assembling supramolecular system which mimics, at a molecular level, the function performed by a macroscopic electrical extension cable. The system is made up of three components, 1²⁺, 2-H³⁺, and 3. Component 1²⁺ consists of two moieties: a [Ru(bpy)₃]²⁺ unit, which plays the role of an electron donor under light excitation, and a DB24C8 crown ether, which fulfills the function of a socket. The wire-type component 2-H³⁺ is also composed of two moieties, a secondary dialkylammonium-ion center and a bipyridinium unit, which thread into the DB24C8 crown ether socket of 1²⁺ and the 1/5DN38C10 crown-ether socket 3, respectively. The photochemical, photophysical, and electrochemical properties of the three separated components, of the 1²⁺ ⊃ 2-H³⁺ and 2-H³⁺ ⊂ 3 dyads, and of the 1²⁺ ⊃ 2-H³⁺ ⊂ 3 triad have been investigated in CH₂Cl₂ solution containing 2% MeCN. Reversible connection/disconnection of the two plug/socket systems can be controlled independently by acid/base and redox stimulation. The behavior of the various different dyads and triad has been monitored by light absorption and emission spectroscopies, as well as by electrochemical techniques. In the fully connected 1²⁺ ⊃ 2-H³⁺ ⊂ 3 triad, light excitation of the [Ru(bpy)₃]²⁺ unit of component 1²⁺ is followed by electron transfer (k = 2.8 x 10⁸ s^-1) to the bipyridinium unit of component 2-H³⁺, which is plugged into component 3. Possible schemes to obtain improved molecular-level electrical extension cables are discussed.