Butterfly-Shaped Dibenz[a,j]anthracenes: Synthesis and Photophysical Properties.

A strategy for the synthesis of dibenz[a,j]anthracenes (DBAs) from cyclohexa-2,5-diene-1-carboxylic acids is presented. Our approach involves sequential C-H olefination, cycloaddition, and decarboxylative aromatization. In the key step for DBA skeleton construction, the bis-C-H olefination products, 1,3-dienes, are utilized as substrates for [4 + 2] cycloaddition with benzyne. This concise synthetic route allows for regioselective ring formation and functional group introduction. The structural features and photophysical properties of the resulting DBA molecules are discussed.

Micropatterned Poly(3,4-ethylenedioxythiophene) Thin Films with Improved Color-Switching Rates and Coloration Efficiency.

Electrochromic materials carry out redox reactions and change their colors upon external bias. These materials are the primary component in constructing smart windows for energy saving in buildings or vehicles. Enhancing the electrochromic performances of the materials is crucial for their practical applications. Micropatterned poly(3,4-ethylenedioxythiophene) (mPEDOT) thin films are electrodeposited on indium tin oxide conducting glass in this study. Their electrochromic properties, including transmittance modulation ability, color-switching rates, and coloration efficiency, are investigated and compared with nonpatterned PEDOT thin films. The mPEDOT thin films exhibited faster coloring and bleaching speeds and higher coloration efficiency than the PEDOT thin films while keeping similar transmittance modulation ability. The results suggest that micropatterning an electrochromic material thin film might enhance its electrochromic performances. This research demonstrates the possibility of promoting the color-switching rate of a PEDOT thin film by micropatterning it.

Nanoscale redox mapping at the MoS2-liquid interface.

Layered MoS2 is considered as one of the most promising two-dimensional photocatalytic materials for hydrogen evolution and water splitting; however, the electronic structure at the MoS2-liquid interface is so far insufficiently resolved. Measuring and understanding the band offset at the surfaces of MoS2 are crucial for understanding catalytic reactions and to achieve further improvements in performance. Herein, the heterogeneous charge transfer behavior of MoS2 flakes of various layer numbers and sizes is addressed with high spatial resolution in organic solutions using the ferrocene/ferrocenium (Fc/Fc+) redox pair as a probe in near-field scanning electrochemical microscopy, i.e. in close nm probe-sample proximity. Redox mapping reveals an area and layer dependent reactivity for MoS2 with a detailed insight into the local processes as band offset and confinement of the faradaic current obtained. In combination with additional characterization methods, we deduce a band alignment occurring at the liquid-solid interface.

Metal organic framework-organic polymer monolith stationary phases for capillary electrochromatography and nano-liquid chromatography.

In this study, metal organic framework (MOF)-organic polymer monoliths prepared via a 5-min microwave-assisted polymerization of ethylene dimethacrylate (EDMA), butyl methacrylate (BMA), and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) with the addition of various weight percentages (30-60%) of porous MOF (MIL-101(Cr)) were developed as stationary phases for capillary electrochromatography (CEC) and nano-liquid chromatography (nano-LC). Powder X-ray diffraction (PXRD) patterns and nitrogen adsorption/desorption isotherms of these MOF-organic polymer monoliths showed the presence of the inherent characteristic peaks and the nano-sized pores of MIL-101(Cr), which confirmed an unaltered crystalline MIL-101(Cr) skeleton after synthesis; while energy dispersive spectrometer (EDS) and micro-FT-IR spectra suggested homogenous distribution of MIL-101(Cr) in the MIL-101(Cr)-poly(BMA-EDMA) monoliths. This hybrid MOF-polymer column demonstrated high permeability, with almost 800-fold increase compared to MOF packed column, and efficient separation of various analytes (xylene, chlorotoluene, cymene, aromatic acids, polycyclic aromatic hydrocarbons and trypsin digested BSA peptides) either in CEC or nano-LC. This work demonstrated high potentials for MOF-organic polymer monolith as stationary phase in miniaturized chromatography for the first time.

Poly(triallyl isocyanurate-co-ethylene dimethacrylate-co-alkyl methacrylate) stationary phases in the chromatographic separation of hydrophilic solutes.

This study describes the ability of triallyl isocyanurate (TAIC)-co-methacrylate ester polymer monoliths as stationary phases for the separation of hydrophilic compounds (phenolic acids, amino acids and catecholamines) in capillary electrochromatography (CEC) and ultra high pressure liquid chromatography (UHPLC). Several TAIC-co-methacrylate ester polymer monoliths prepared by single-step in situ copolymerization of TAIC, ethylene dimethacrylate (EDMA) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS), with or without alkyl methacrylates were characterized by examining the SEM image, surface area, contact angle, and the thermal decomposition temperature. Compared to the conventional methacrylate ester-based monoliths, these proposed monoliths possessed hydrophilic character thus increased wettability which improved chromatographic separation selectivity of polar phenolic acids. Among the proposed TAIC-co-methacrylate monoliths, poly(TAIC-co-EDMA-AMPS-co-stearyl methacrylate (SMA)) showed separation selectivity with an increased analyte resolution from 0.0 to 0.92 for 4-hydroxybenzoic acid and vanillic acid, which were consistently difficult to resolve in the reversed-phase chromatographic mechanism of these monoliths in aqueous mobile phases. Moreover, stable ionization efficiencies were observed when this monolith was combined with ESI-MS detector possibly because an organic solvent-rich sheath liquid was used in the CEC-MS. This study demonstrates the potentiality of novel TAIC-co-methacrylate polymer monoliths in hydrophilic solute separation either in CEC or UHPLC mode.

Capillary electrochromatography-mass spectrometry determination of melamine and related triazine by-products using poly(divinyl benzene-alkene-vinylbenzyl trimethylammonium chloride) monolithic stationary phases.

In this study, a capillary electrochromatography (CEC) method coupled either with UV or mass spectrometric detection was developed for the detection of trace-amounts of melamine and its related by-products (ammeline, ammelide, and cyanuric acid). A series of poly(divinyl benzene-alkene-vinylbenzyl trimethylammonium chloride) monolithic columns, which were prepared by a simple in situ polymerization with divinyl benzene (DVB), vinylbenzyl trimethylammonium chloride (VBTA) and different types of alkene monomers such as 1-octene, 1-dodecene or 1-octadecene were used as separation columns, with the poly(DVB-1-dodecene-VBTA) monolith as the optimal chromatographic material because it provided a better separation. The detection limits of four melamine derivatives were in the ranged of 0.6-2.18 mg L(-1) by the optimal CEC-UV mode, and were reduced from 2.2 to 19.4 µg L(-1) by the optimal CEC-MS mode. Finally, the proposed CEC methods successfully determined melamine contaminations (0.1 mg L(-1) per analyte) in several dairy products as test samples with analyte recovery range of 69-85% (intra-day) and 68-75% (inter-day), and with peak area reproducibility range of 4.3-8.6% and 8.7-15.6% for intra-day and inter-day, respectively. This is the first report for CEC separation coupled with MS detection applied in trace melamine residue analyses with a faster separation and comparable or even better detection ability than previous GC-MS, CE-MS, as well as LC-MS methods.

Analyses of synthetic antioxidants by capillary electrochromatography using poly(styrene-divinylbenzene-lauryl methacrylate) monolith.

In this study, several organic polymer-based monoliths prepared by single step in situ copolymerization of styrene- and methacrylate ester-based monomers (styrene (S), divinylbenzene (DVB) and lauryl methacrylate (LMA)) were developed as stationary phases of capillary electrochromatography (CEC) for the analyses of synthetic antioxidants. These monoliths were characterized by examining the SEM image, IR spectrum, and measuring the pore size, surface area, conversion yield, and thermal decomposition temperature. The polymerization procedure was optimized by varying the reaction temperature, the reaction time, and the LMA-styrene ratio. The LMA-styrene ratio had the most significant influence on the peak symmetry of butylated hydroxyanisole (BHA) and 2, 6-di-tert-butyl-4-methyl phenol (BHT), the latter being greatly affected by excessive peak tailing in the poly(S-DVB) monolith. It showed that the interaction between the poly(S-DVB) monolith and the antioxidant (BHT or BHA) was significantly altered by the insertion of LMA. Compared with the best HPLC and CE methods previously reported, this proposed CEC method provides a comparable separation ability for the five antioxidants analyzed. This study demonstrates that the potentiality of poly(S-DVB-LMA) monolith as stationary phase, especially for CEC system, because of high thermal stability and good column reproducibility.

Analyses of sulfonamide antibiotics by CEC using poly(divinylbenzene-1-octadecene-vinylbenzyl trimethyl ammonium chloride) monolithic columns.

In this study, a series of novel polymeric monolithic columns prepared by single-step in situ copolymerization of 1-octadecene (OD), divinylbenzene (DVB) and/or styrene (S), were developed as separation columns for the sulfonamide analyses. On the CEC method, the composition of monomer mixtures (i.e. the ratio of S versus OD), content of charge-bearing monomer (vinylbenzyl trimethylammonium chloride) and volume fraction ratio of ACN in the mobile phase, was found to be the predominant influences for sulfonamide separation. Furthermore, an online sample concentration step, field-amplified sample injection, was used to enhance the detection sensitivity of sulfonamides. Sample matrix's pH had a significant effect on the sulfonamide sensitivity. For the eight sulfonamides, the proposed poly(DVB-OD) monolithic stationary phase coupled with field-amplified sample injection step could achieve a reproducible baseline separation within 15 min and LODs in the range of 8.1-28.2 microg/L.

Micropipet delivery-substrate collection mode of scanning electrochemical microscopy for the imaging of electrochemical reactions and the screening of methanol oxidation electrocatalysts.

The micropipet delivery-substrate collection (MD-SC) mode of scanning electrochemical microscopy (SECM) is demonstrated. This new mode is intended for the study and imaging of electrochemical as well as electrocatalytic reactions of neutral species that cannot be generated electrochemically. The spontaneous transfer of the analyte from an organic solvent across an interface between two immiscible electrolyte solutions (ITIES) and its diffusion into the aqueous solution served as the mechanism to deliver it to the substrate, where the corresponding electrochemical or electrocatalytic reaction is carried out. High-resolution SECM images of ferrocenemethanol (FcMeOH) oxidation, benzoquinone (BQ) reduction, and the formic acid oxidation reaction (FAOR) at a Pt microelectrode substrate were successfully acquired. Furthermore, this new mode was used for the screening of electrocatalyst arrays for the methanol oxidation reaction (MOR), with the optimization of an efficient candidate, Pt(80)Ce(20). Digital simulations produced quantitative information about the expected current response at the substrate in the proposed MD-SC mode of SECM.

Electrocatalytic activity of Pd-Co bimetallic mixtures for formic acid oxidation studied by scanning electrochemical microscopy.

The electrochemical oxidation of formic acid was studied by the tip generation-substrate collection (TG-SC) mode of scanning electrochemical microscopy (SECM), extending the number of applications of SECM in electrocatalysis. Formic acid was generated at a Hg on Au ultramicroelectrode (UME) tip by reduction of CO(2) in a 0.1 M KHCO(3) solution saturated with this gas. The electrocatalytic activity of different Pd-Co bimetallic compositions was evaluated using a Pd-Co electrocatalyst array formed by spots deposited onto glassy carbon (GC) as a SECM substrate. The SECM tip, which generated a constant formic acid flux, was scanned above the array and the oxidation current generated when formic acid was collected by active electrocatalytic spots was displayed as a function of tip position. This generated a SECM image that showed the electrocatalytic activity of each spot. SECM screening identified Pd(50)Co(50) (Pd/Co = 50:50, atomic ratio) as a better electrocatalyst toward the formic acid oxidation than pure Pd or Pt in 0.1 M KHCO(3) solution and this result was confirmed by cyclic voltammetry. Positive feedback was observed for the most active compositions of Pd-Co which suggests fast reaction kinetics and chemical reversibility during the oxidation of formic acid to CO(2). Moreover this feedback increases the contrast between active and non-active spots in this imaging mode.

Electrochemical oxidation of double-stranded polybisnorbornenes containing linearly aligned ferrocene linkers.

Seventy percent of the ferrocene moieties in double-stranded polybisnorbornenes containing linearly aligned ferrocene linkers are oxidised and each of the neighbouring monomeric units in these polymers may strongly interact with each other; the oxidised form of has been shown to be antiferromagnetic.

Combining light harvesting and electron transfer in silica-titania-based organic-inorganic hybrid materials.

A convenient protocol to fabricate an organic-inorganic hybrid system with covalently bound light-harvesting chromophores (stilbene and terphenylene-divinylene) and an electron acceptor (titanium oxide) is described. Efficient energy- and electron-transfer processes may take place in these systems. Covalent bonding between the acceptor chromophores and the titania/silica matrix would be important for electron transfer, whereas fluorescence resonant energy transfer (FRET) would strongly depend on the ratio of donor to acceptor chromophores. Time-resolved spectroscopy was employed to elucidate the detailed photophysical processes. The coupling of FRET and electron transfer was shown to work coherently to lead to photocurrent enhancement. The photocurrent responses reached a maximum when the hybrid-material thin film contained 60 % acceptor and 40 % donor.

Sequential electrochemical oxidation of alternating benzene-furan oligomers.

Electrochemical oxidation of pentaaryl 2 containing two furan moieties occurs sequentially to give diketone 8 after two-electron transfer. Further oxidation with another two-electron transfer gives the corresponding tetraketone 9. Radical cation intermediate is detected by absorption spectroscopy. The radical intermediates of different regiochemistry have been shown to exhibit different oxidation potentials as revealed by the differential pulse voltammetry.

Convergent/divergent synthesis and photophysical studies of alternating benzene-furan oligoaryls from substituted propargylic dithioacetals.

A range of oligoaryls that contain alternating benzene-furan rings is synthesized by a rapid convergent/divergent method from the annulation of a propargylic dithioacetal and an aldehyde with a propargylic dithioacetal moiety as a substituent. These oligomers are fairly soluble in a range of organic solvents and can be easily purified by reprecipitation. The substituents on the furan rings can be varied according to the substituents in the starting propargylic dithioacetals. This route provides a useful procedure for the synthesis of alternating benzene-furan oligomers without repeated units. These furan-containing oligoaryls are highly fluorescent in the visible region and are electrochemically active. The band gaps of these oligomers appear to be less sensitive towards changes in conjugation length than those of oligofurans.

Furan-containing oligoaryl cyclophanene.

[structure: see text] Furan-containing oligoaryl cyclophanene 1 and the corresponding cyclophane 2 were synthesized from propargylic dithioacetal 3. The electrochemical and photophysical properties and the fluxional behavior of these molecules have been examined. The emission of 1 appeared at 499 nm whereas that of 2 appeared at 389 nm.