RATIONAL DESIGN OF A LIGHT-DRIVEN MOLECULAR SWITCH INCORPORATING AN ALIZARIN-RU(BPY)(2) FRAGMENT

Ab initio and semiempirical AM1 studies are reported concerning the mechanism of a recently observed reversible acid-induced Linkage isomerization in bis(bipyridine)(alizarin)ruthenium(II), where alizarin = 1,2-dihydroxy-9,-10-anthraquinone. The calculations indicate that initial protonation occurs at the alizarin O(1), followed by a concerted proton shift to O(2) and 1,2 --> 1,9 isomerization. The effects of protonation at various sites on the alizarin moiety on the metal to ligand bond orders and isomerization barriers are reported. The theoretically determined mechanism strongly suggests the possibility of utilizing the alizarin-Ru(bpy)(2) isomerization process as the basis for a novel reversible photodriven molecular switch. A prototypical molecular switch is discussed, and its switching mechanism and thermochemistry are investigated by further AM1 calculations.