Surface Electrochemistry And Bio-Chemistry Systems Based On Photochromic Molecular Switches

During the photoisomerization process, several photochemical and photophysical properties of photochromic materials, such as absorption spectra, emission spectra, dielectric constant, refraction index, redox potential, conjugation, paramagnetic property, dipole property, steric structure and etc., will undergo a distinct change. As reversible molecular switches, photochromic compounds have been widely used in mimicking operations of electronic devices. However, solution systems nowadays no longer meet the requirements of further development and application of photo-switchable materials. To solve this problem, photochromic materials recently have joined in other fields such as surfacial materials, nano-technology and biological systems. This paves a way for the rise of photochromic material family in future scientific research and daily applications.Chapter I:The development and application of photochromic materials are reviewed.Chapter II:A novel gated photochromic compound Nap-Pip-DTE was prepared to mimic a soft gear-shift based on alternative UV/Vis irradiation, protonation/deprotonation and copper (Ⅱ) ion complexation/dissociation. The fluorescence and absorption spectra were used as output signals. Copper (Ⅱ) ion was introduced to mimic the parking (P) state by complexation with two intramolecular piperazine moieties of Nap-Pip-DTE, transforming diarylethene moieties into the photo-inactive parallel form.Chapter III:A dithienylethene derivative was covalently linked to a cysteamine monolayer associated with a Au surface to yield a photoisomerizable monolayer. Electrochemical and XPS analyses reveal that the association of metal ions to themono layer is controlled by its photoisomerization state.We find that Cu2+/Ag+ions reveal a high affinity for the open monolayer state, whereas the closed monolayer state exhibits a substantially lower binding affinity for Cu2+/Ag+.Chapter Ⅳ:The thermosensitive p-NIPAM is electropolymerized onto Au surfaces. The incorporation of the photoisomerizable spiropyran compound into p-NIPAM allows the reversible photochemical control of the gel-to-solid phase-transition temperatures of the polymer. Whereas the gel to solid phase-transition temperature of the spiropyran-modified p-NIPAM is33±2℃, the phase-transition temperature of the merocyanine-functionalized p-NIPAM matrix corresponds to38±1℃Upon the incorporation of Pt nanoparticles (NPs) into the photochemically controlled p-NIPAM, a hybrid photoswitchable electrocatalytic matrix is formed. At a fixed temperature corresponding to36℃, the effective electrocatalytic reduction of H2O2, or the oxidation of ascorbic acid, proceeded in the presence of the merocyanine-functionalized p-NIPAM, yet these electrocatalytic transformations were inhibited in the presence of the nitrospiropyran-modified p-NIPAM.Chapter Ⅴ: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 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>530nm) and the reversible photoizomerization of the open substrate to the closed state (λ=302nm), the cyclic photonic uptake and release of the closed substrate to and from the imprinted Au NPs matrix are demonstrated.Chapter Ⅵ:In this chapter, we show that the integration of para-sulfonato-calix[4]arene with the pore of a-hemolysin regulates its open-pore properties. Using the gating property of a-hemolysin, we studied the host-guest interactions between para-sulfonato-calix[4]arene and4,4’-dipyridinium-azobenzene at the single-molecule level Subsequently, we have extended the application of this gating system to the single-molecule study of light-induced molecule shuttle based on para-sulfonato-calix[4]arene and4,4’-dipyridinium-azobenzene. These experiments highlight the possibility to fabricate a-hemolysin based arrays to study the motions of individual molecular machines.Chapter Ⅶ:In this chapter, some other works are illustrated.Chapter Ⅷ:Conclusion.