Visible Light-Driven Artificial Molecular Switch Actuated by Radical-Radical and Donor-Acceptor Interactions

We describe a visible light-driven switchable [2]catenane, composed of a Ru(bpy)₃²⁺ tethered cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺) ring that is interlocked mechanically with a macrocyclic polyether consisting of electron-rich 1,5-dioxynaphthalene (DNP) and electron-deficient 4,4′-bipyridinium (BIPY²⁺) units. In the oxidized state, the CBPQT⁴⁺ ring encircles the DNP recognition site as a consequence of favorable donor-acceptor interactions. In the presence of an excess of triethanolamine (TEOA), visible light irradiation reduces the BIPY²⁺ units to BIPY^(•+) radical cations under the influence of the photosensitizer Ru(bpy)₃²⁺, resulting in the movement of the CBPQT^2(•+) ring from the DNP to the BIPY^(•+) recognition site as a consequence of the formation of the more energetically favorable trisradical complex, BIPY^(•+) CBPQT^2(•+). Upon introducing O₂ in the dark, the BIPY^(•+) radical cations are oxidized back to BIPY²⁺ dications, leading to the reinstatement of the CBPQT⁴⁺ ring encircled around the DNP recognition site. Employing this strategy of redox control, we have demonstrated a prototypical molecular switch that can be manipulated photochemically and chemically by sequential reduction and oxidation.