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)(3)(2+) tethered cyclobis (paraquat-p-phenylene) (CBPQT(4+)) 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 CBPQT(4+) 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((center dot+)) radical cations under the influence of the photosensitizer Ru(bpy)(3)(2+), resulting in the movement of the CBPQT2(center dot+) ring from the DNP to the BIPY(center dot+) recognition site as a consequence of the formation of the more energetically favorable trisradical complex, BIPY(center dot+) C CBPQT2(center dot+). Upon introducing O-2 in the dark, the BIPY(center dot+) radical cations are oxidized back to BIPY2+ dications, leading to the reinstatement of the CBPQT(4+) 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.