Photochemically-, Chemically-, and pH-Controlled Electrochemistry at Functionalized Spiropyran Monolayer Electrodes

Abstract

A photoisomerizable nitrospiropyran monolayer assembled on a Au electrode provides a functionalized interface for the photochemical, pH, and thermal control of electrochemical processes of charged electroactive redox probes. (Mercaptobutyl)nitrospiropyran 1 was assembled as a monolayer on a Au electrode. The monolayer exhibits reversible photoisomerizable features, and illumination of the nitrospiropyran monolayer, SP state, 320 nm < λ < 350 nm, yields at pH = 7.0 the protonated nitromerocyanine monolayer state, MRH+ state. Further irradiation of the MRH+ monolayer, λ > 495 nm, regenerates the SP state of the monolayer. The light-induced transformation of the monolayer between a neutral and a positively-charged interface allows the control of the electron transfer processes at the electrode interface. Electrooxidation of the negatively-charged (3,4-dihydroxyphenyl)acetic acid, DHPAA, is enhanced at the MRH+ monolayer electrode as compared to the SP-functionalized monolayer electrode. Electrooxidation of the positively-charged 3-hydroxytyramine (dopamine), DOPA, is inhibited at the MRH+ monolayer electrode as compared to its oxidation by the SP monolayer electrode. The control of the electrochemical oxidation of DHPAA and DOPA at the photoisomerizable monolayer electrode is attributed to the electrostatic interactions of the MRH+ monolayer electrode with the redox-active substrates. Electrostatic attraction of DHPAA and repulsion of DOPA by the MRH+ monolayer results in enhancement or inhibition of the electrochemical processes, respectively. By reversible isomerization of the monolayer between the SP and MRH+ states, cyclic amperometric transduction of the optical signals recorded by the monolayer is accomplished. In the presence of a mixture of oppositely-charged redox substrates, i.e. DHPAA and 2,5-bis[[2-(dimethylbutylammonio)ethyl]amino]-1,4-benzoquinone (3) or pyrroloquinoline quinone, PQQ, (4) and 3, photostimulated selective electrochemistry is accomplished in the presence of the photoisomerizable monolayer electrode. The transformation of the protonated nitromerocyanine monolayer, MRH+ state, generated at pH = 7.0, to the zwitterionic nitromerocyanine configuration, MR± state at higher pH, allows the pH-controlled electrooxidation of DHPAA and DOPA at the monolayer electrode. Similarly, thermal isomerization of the SP monolayer electrode, pH = 7.0, 60 °C, yields the MRH+ monolayer electrode. These thermochromic features of the monolayer are employed to respectively activate or deactivate the electrooxidation of DHPAA or DOPA at the functionalized electrode. By cyclic thermal isomerization of the SP monolayer to the MRH+ monolayer followed by photochemical isomerization of the MRH+ monolayer followed by photochemical isomerization of the MRH+ monolayer to the SP state, λ > 495 nm, the thermochromic and photochromic features of the monolayer are amperometrically transduced via the oxidation of DHPAA and DOPA, respectively. Electrochemical oxidation of DHPAA and DOPA is further accomplished by the applicatio...

Oxidative Electrochemical Switching in Dithienylcyclopentenes, Part 1: Effect of Electronic Perturbation on the Efficiency and Direction of Molecular Switching

“…The photochromic process is quite robust with regard to the environment, and indeed several studies have demonstrated the application of dithienylethene- [7] and spiropyran-based [8] compounds in modified electrode devices. Recently, we demonstrated one-way optoelectronic switching of dithienylethenes on gold using breakjunction techniques.…”

Oxidative Electrochemical Switching in Dithienylcyclopentenes, Part 2: Effect of Substitution and Asymmetry on the Efficiency and Direction of Molecular Switching and Redox Stability

“…These studies have focussed on understanding the factors which control their photophysical and electrochemical properties. Although the photochromic behaviour of materials based on diarylethenes, fulgides [7] and spiropyrans has been investigated extensively in recent years and has been adapted to drive changes in bulk material properties, [8][9][10][11][12][13] a detailed understanding of the electrochemical properties of these systems is not yet available, and relatively few studies have been reported in the literature. [14][15][16] In Part 1, we examined the electrochemical and spectroelectrochemical properties of two representative sets of dithienylethene switches (1 Ho/1 Fo and 2 Ho/2 Fo, Scheme 1) and investigated the mechanism and solvent dependence of the electrochemically driven ring-opening/closing processes.…”

Photochemical and Electrochemical Encoding of Erasable Magnetic Patterns

“…[25] Treatment of the surface with the Co 2+ solution resulted in the association of the Co 2+ ions only to the nitromerocyanine sites (1 a; Scheme 1). The subsequent electrochemical reduction of the Co 2+ ions yielded a magnetic pattern composed of the Co 0 NPs (Figure 3 It should be noted that in the absence of cobalt species the photogenerated nitromerocyanine (1 a) patterns can be erased by irradiation of the surface with visible light, resulting in photochemical isomerization to the nitrospiropyran (1 b) state.…”