Electrochemically Triggered Au Nanoparticles “Sponges” for the Controlled Uptake and Release of a Photoisomerizable Dithienylethene Guest Substrate

Abstract

1,2-Di(2-methyl-5-(N-methylpyridinium)-thien-3-yl)-cyclopentene undergoes a reversible photoisomerization between open and closed states. The closed isomer state exhibits electron acceptor properties, whereas its irradiation using visible light (λ > 530 nm) yields the open state that lacks electron acceptor features. The electropolymerization of thioaniline-functionalized Au nanoparticles (NPs) in the presence of the closed photoisomer state yields a molecularly imprinted Au NPs matrix, cross-linked by redox-active bis-aniline π-donor bridges. The closed isomer is stabilized in the imprinted sites of the bis-aniline-bridged Au NPs composite by donor-acceptor interactions. The electrochemical oxidation of the bis-aniline bridging units to the quinoid acceptor state leads to imprinted sites that lack affinity interactions for the binding of the closed state to the matrix, leading to the release of the closed photoisomer to the electrolyte solution. By the cyclic reduction and oxidation of the bridging units to the bis-aniline and quinoid states, the reversible electrochemically controlled uptake and release of the closed photoisomer is demonstrated. The quantitative uptake and release of the closed isomer to and from the imprinted Au NPs composites is followed by application of CdSe/ZnS quantum dots as auxiliary probes. Similarly, by the reversible photochemical isomerization of the closed substrate to the open substrate (λ > 530 nm) and the reversible photoizomerization of the open substrate to the closed state (λ = 302 nm), the cyclic photonic uptake and release of the closed substrate to and from the imprinted Au NPs matrix are demonstrated. Finally, we demonstrate that the electrochemically stimulated uptake and release of the closed substrate to and from the imprinted Au NPs composite controls the wettability of the resulting surface.