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 me chanism of a recently observed reversible acid-induced Linkage isomeri zation 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 prot on shift to O(2) and 1,2 --> 1,9 isomerization. The effects of protona tion at various sites on the alizarin moiety on the metal to ligand bo nd orders and isomerization barriers are reported. The theoretically d etermined mechanism strongly suggests the possibility of utilizing the alizarin-Ru(bpy)(2) isomerization process as the basis for a novel re versible photodriven molecular switch. A prototypical molecular switch is discussed, and its switching mechanism and thermochemistry are inv estigated by further AM1 calculations.