Multi-stimuli Photo and Redox-active Nanostructured Mesoporous Silica Films on Transparent Electrodes

Reversible Photochromism of 4,4'-Disubstituted 2,2'-Bipyridine in the Presence of SO3

We report an unusual photochromic behavior of 4,4'-disubstituted-2,2'-bipyridine. It was found that in the presence of a SO3 source and HCl, 2,2'-bipyridine-4,4'-dibutyl ester undergoes a color change from yellow to magenta in solution with maximum absorbance at 545 nm upon irradiation with 395 nm light. The photochromism is thermally reversible in solution. Different from the known bipyridine-based photoswitching pathways, the photo response does not involve any metal which form colored complexes or the formation of colored free radical cations like the photo-reduction of viologens. A combination of experimental and computational analysis was used to probe the mechanism. The results suggest the colored species to be a complex formed between N-oxide of the 2,2'-bipyridine-4,4'-dibutyl ester and SO2; the N-oxide and SO2 are formed from photoactivated oxidation of the bipyridine with SO3 serving as the oxygen source. This complex represents a new addition to the library of photoswitches that is easy to synthesize, reversible in solution, and of high fatigue resistance, making it a promising candidate for applications in photo-switchable materials and SO3 detection. We also demonstrated experimentally similar photochromic behaviors with 2,2'-bipyridine-containing polymers.

Composite Silica-Based Films as Platforms for Electrochemical Sensors

Sol-gel-derived silica thin films generated onto electrode surfaces in the form of organic-inorganic hybrid coatings or other composite layers have found tremendous interest for being used as platforms for the development of electrochemical sensors and biosensors. After a brief description of the strategies applied to prepare such materials, and their interest as electrode modifier, this review will summarize the major advances made so far with composite silica-based films in electroanalysis. It will primarily focus on electrochemical sensors involving both non-ordered composite films and vertically oriented mesoporous membranes, the biosensors exploiting the concept of sol-gel bioencapsulation on electrode, the spectroelectrochemical sensors, and some others.

Doping of Transparent Electrode Based on Oriented Networks of Nickel in Poly(3,4-Ethylenedioxythiophene) Polystyrene Sulfonate Matrix with P-Toluenesulfonic Acid

This work aimed to obtain an optically transparent electrode based on the oriented nanonetworks of nickel in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate matrix. Optically transparent electrodes are used in many modern devices. Therefore, the search for new inexpensive and environmentally friendly materials for them remains an urgent task. We have previously developed a material for optically transparent electrodes based on oriented platinum nanonetworks. This technique was upgraded to obtain a cheaper option from oriented nickel networks. The study was carried out to find the optimal electrical conductivity and optical transparency values of the developed coating, and the dependence of these values on the amount of nickel used was investigated. The figure of merit (FoM) was used as a criterion for the quality of the material in terms of finding the optimal characteristics. It was shown that doping PEDOT: PSS with p-toluenesulfonic acid in the design of an optically transparent electroconductive composite coating based on oriented nickel networks in a polymer matrix is expedient. It was found that the addition of p-toluenesulfonic acid to an aqueous dispersion of PEDOT: PSS with a concentration of 0.5% led to an eight-fold decrease in the surface resistance of the resulting coating.

Weak Coordinating Character of Organosulfonates in Oriented Silica Films: An Efficient Approach for Immobilizing Cationic Metal-Transition Complexes

Iron (II) tris(2,2′-bipyridine) complexes, [Fe(bpy)3]2+, have been synthesized and immobilized in organosulfonate-functionalized nanostructured silica thin films taking advantage of the stabilization of [Fe(H2O)6]2+ species by hydrogen bonds to the anionic sulfonate moieties grafted to the silica nanopores. In a first step, thiol-based silica films have been electrochemically generated on indium tin oxide (ITO) substrates by co-condensation of 3-mercaptopropyltrimethoxysilane (MPTMS) and tetraethoxysilane (TEOS). Secondly, the thiol function has been modified to sulfonate by chemical oxidation using hydrogen peroxide in acidic medium as an oxidizing agent. The immobilization of [Fe(bpy)3]2+ complexes has been performed in situ in two consecutive steps: (i) impregnation of the sulfonate functionalized silica films in an aqueous solution of iron (II) sulfate heptahydrate; (ii) dipping of the iron-containing mesostructures in a solution of bipyridine ligands in acetonitrile. The in situ formation of the [Fe(bpy)3]2+ complex is evidenced by its characteristic optical absorption spectrum, and elemental composition analysis using X-ray photoelectron spectroscopy. The measured optical and electrochemical properties of immobilized [Fe(bpy)3]2+ complexes are not altered by confinement in the nanostructured silica thin film.