Functionalization of Conductive Polymers through Covalent Postmodification

Organic chemical reactions have been used to functionalize preformed conducting polymers (CPs). The extensive work performed on polyaniline (PANI), polypyrrole (PPy), and polythiophene (PT) is described together with the more limited work on other CPs. Two approaches have been taken for the functionalization: (i) direct reactions on the CP chains and (ii) reaction with substituted CPs bearing reactive groups (e.g., ester). Electrophilic aromatic substitution, S_EAr, is directly made on the non-conductive (reduced form) of the CPs. In PANI and PPy, the N-H can be electrophilically substituted. The nitrogen nucleophile could produce nucleophilic substitutions (SN) on alkyl or acyl groups. Another direct reaction is the nucleophilic conjugate addition on the oxidized form of the polymer (PANI, PPy or PT). In the case of PT, the main functionalization method was indirect, and the linking of functional groups via attachment to reactive groups was already present in the monomer. The same is the case for most other conducting polymers, such as poly(fluorene). The target properties which are improved by the functionalization of the different polymers is also discussed.

Counter Electrode Impact on Quantum Dot Solar Cell Efficiencies

The counter electrode (CE), despite being as relevant as the photoanode in a quantum dot solar cell (QDSC), has hardly received the scientific attention it deserves. In this study, nine CEs (single-walled carbon nanotubes (SWCNTs), tungsten oxide (WO₃), poly(3,4-ethylenedioxythiophene) (PEDOT), copper sulfide (Cu₂S), candle soot, functionalized multiwalled carbon nanotubes (F-MWCNTs), reduced tungsten oxide (WO_3-x), carbon fabric (C-Fabric), and C-Fabric/WO_3-x) were prepared by using low-cost components and facile procedures. QDSCs were fabricated with a TiO₂/CdS film which served as a common photoanode for all CEs. The power conversion efficiencies (PCEs) were 2.02, 2.1, 2.79, 2.88, 2.95, 3.78, 3.66, 3.96, and 4.6%, respectively, and the incident photon to current conversion efficiency response was also found to complement the PCE response. Among all CEs employed here, C-Fabric/WO_3-x outperforms all the other CEs, for the synergy between C-Fabric and WO_3-x comes to the fore during cell operation. The low sheet resistance of C-Fabric and its high surface area due to the meshlike morphology enables high WO_3-x loading during electrodeposition, and the good electrocatalytic activity of WO_3-x, the very low overpotential, and its high electrical conductivity that facilitate electron transfer to the electrolyte are responsible for the superior PCE. WO₃-based electrodes have not been used until date in QDSCs; the ease of fabrication of WO₃ films and their good chemical stability and scalability also favor their application to QDSCs. Futuristic possibilities for other novel composite CEs are also discussed. We anticipate this study to be useful for a well-rounded development of high-performance QDSCs.

Exploring the flexible chemistry of 4-fluoro-3-nitrophenyl azide for biomolecule immobilization and bioconjugation

Bioconjugation and functionalization of polymer surfaces are two major tasks in materials chemistry which are accomplished using a variety of coupling agents. Immobilization of biomolecules onto polymer surfaces and the construction of bioconjugates are essential requirements of many biochemical assays and chemical syntheses. Different linkers with a variety of functional groups are used for these purposes. Among them, the benzophenones, aryldiazirines, and arylazides represent the most commonly used photolinker to produce the desired chemical linkage upon their photo-irradiation. In this review, we describe the versatile applications of 4-fluoro-3-nitrophenyl azide, one of the oldest photolinkers used for photoaffinity labeling in the late 1960s. Surprisingly, this photolinker, historically known as 1-fluoro-2-nitro-4-azidobenzene (FNAB), has remained unexplored for a long time because of apprehension that FNAB forms ring-expanded dehydroazepine as a major product and hence cannot activate an inert polymer. The first evidence of photochemical activation of an inert surface by FNAB through nitrene insertion reaction was reported in 2001, and the FNAB-activated surface was found to conjugate a biomolecule without any catalyst, reagent, or modification. FNAB has distinct advantages over perfluorophenyl azide derivatives, which are contemporary nitrene-generating photolinkers, because of its simple, single-step preparation and ease of thermochemical and photochemical reactions with versatile polymers and biomolecules. Covering these aspects, the present review highlights the flexible chemistry of FNAB and its applications in the field of surface engineering, immobilization of biomolecules such as antibodies, enzymes, cells, carbohydrates, oligonucleotides, and DNA aptamers, and rapid diagnostics. Graphical Abstract An overview of the FNAB-engineered activated polymer surfaces for covalent ligation of versatile biomolecules.

Dopamine amperometric detection at a ferrocene clicked PEDOT:PSS coated electrode

Chemically modified electrodes are widely employed in electroanalytical chemistry and an important goal is to strongly anchor redox mediators on the electrode surface. In this work, indium tin oxide (ITO) electrodes have been coated with PEDOT:PSS that has been ferrocene-functionalized, by a two-step procedure consisting of the electrodeposition of PEDOT-N₃ followed by copper-catalyzed azide-alkyne cycloaddition of ethynylferrocene. The coated electrodes have been characterized by XPS, showing successful ferrocene immobilization, by AFM, and by cyclic voltammetry (CV), which is dominated by the stable and highly reversible response of ferrocene. The electrocatalytical performance of the device is assessed by analyzing 3,4-dihydroxyphenyl ethylamine, also commonly known as dopamine (DA). The sensor presents a linear range between 0.01 and 0.9 mM, a mean sensitivity of 196 mA M^-1 cm^-2 and a limit of detection (LoD) of 1 µM.

The influence of charge trapping on the electrochromic performance of poly(3,4-alkylenedioxythiophene) derivatives

This paper describes the electrochromic properties of a series of poly(3,4-alkylenedioxythiophene) (PXDOT) derivatives featuring various ring sizes and substitutions. The presence of a bulky group on the monomer resulted in a polymer possessing a more-open morphology, which promoted reversible ionic transfer. We used an electrochemical quartz crystal microbalance and cyclic voltammetry to investigate the properties of these polymers. We found that both cations and anions were involved in the charge compensation process. Furthermore, PXDOT derivatives possessing larger ring sizes and/or longer alkyl substituents exhibited less trapping of ions within the polymer during the redox process. The long-term electrochromic stability of these PXDOTs depended strongly on the number of trapped ions. Although the transmittance attenuation of poly(3,4-ethylenedioxythiophene) (PEDOT) decreased from 53 to 42%, we observed no significant decay for poly(diethyl-3,4-dihydro-2H-thieno[3,4-b]-[1,4]dioxepine) (PProDOT-Et(2)) after 400 cycles.

Solvent-annealing-induced self-organization of poly(3-hexylthiophene), a high-performance electrochromic material

We have systematically studied the self-organization of poly(3-hexylthiophene) (P3HT), an electrochromic material, upon control of the solvent evaporation rate. We characterized these polymer films using atomic force microscopy and X-ray diffraction measurements. Well-ordered P3HT structures were developed after solvent annealing; these highly crystalline structures exhibited enhanced electrochromic contrast and reduced resistance within the film, leading to larger coloration efficiencies and faster switching times. The optical contrast (Delta%T), coloration efficiency, and switching time of the P3HT films increased from 54.2%, 182.6 cm(2) C(-1), and 5.3 s, respectively, prior to solvent annealing to 64.8%, 293.5 cm(2) C(-1), and 3.2 s, respectively, after application of the solvent-annealing conditions.