A photoactivated 'molecular train' for optoelectronic applications: Light-stimulated translocation of a β-cyclodextrin receptor within a stoppered azobenzene-alkyl chain supramolecular monolayer assembly on a Au-electrode

A light-driven molecular shuttle is organized on a gold electrode surface. The assembly consists of a ferrocene-functionalized β-cyclodextrin, Fc-β-CD, molecule threaded on a monolayer-immobilized long alkyl component containing a photoisomerizable azobenzene unit, and terminated with a bulky anthracene group. The Fc-β-CD resides preferentially on the trans-azobenzene component, and photoisomerization of the trans-azobenzene to the cis-azobenzene state causes the translocation of the Fc-β-CD to the alkyl-chain component of the assembly. The state of the molecular shuttle is electronically transduced by chronoamperometry. The interfacial electron transfer rate constants for the oxidation of the ferrocene units of Fc-β-CD in the respective positions are k_t=65 s^-1 and k_c=15 s^-1. The light-driven translocation of Fc-β-CD is reversible, and proceeds by the cyclic isomerization of the azobenzene component between the trans and cis states.