Layered molecular optoelectronic assemblies

Abstract

Layered functionalized electrodes are used as optoelectronic assemblies for the electronic transduction of recorded photonic signals. Functionalization of a Au electrode with a photoisomerizable redox-activated monolayer enables the amperometric transduction of the photonic information recorded by the interface. This is exemplified with the organization of a phenoxynaphthacenequinone monolayer (1a). Organization of a photoactivated command layer on an electrode can be used to control interfacial electron transfer and might be applied for the electrical transduction of recorded optical signals. This is addressed with the assembly of a nitrospiropyran photoisomerizable monolayer (2a) on a Au electrode which acts as a command surface for controlling by light interfacial electron transfer. The monolayer undergoes photoisomerization between the neutral state (2a) and the positively charged protonated merocyanine state (2b). The charged interface controls the oxidation of dihydroxyphenylacetic acid, DHPAA (3), and of 3-hydroxytyramine, DOPA (4), and the system is used for the electrochemical transduction of optical signals recorded by the monolayer. Functionalization of electrodes with a β-cyclodextrin monolayer or with an eosin π-donor layer enables the light-stimulated association or dissociation of the photoisomerizable N,N′-bipyridinium azobenzene (5t) and of bis-pyridinium azobenzene (8t) to or from the modified surfaces. Association and dissociation of the surface-associated supramolecular complexes are transduced by electrochemical or piezoelectrical signal outputs. The organization of a supramolecular system where a molecular component is translocated by light-signals between two distinct positions enables one to design ‘molecular machines’. This is exemplified by the organization of a molecular assembly consisting of a ferrocene-functionalized β-cyclodextrin (11) threaded onto an azobenzene-alkyl chain wire and stoppered with an anthracene barrier which acts as a nanoscale molecular machine, a light-stimulated ‘molecular train’. The ferrocene-functionalized β-cyclodextrin is reversibly translocated between the trans-azobenzene and the alkyl chain by cyclic light-induced isomerization of the photoactive monolayer. The position of the β-cyclodextrin receptor is transduced by its chronoamperometric response.