Electron-deficient Groups Research Articles

Reaction‐Based Colorimetric and Ratiometric Fluorescence Sensor for Detection of Cyanide in Aqueous Media

A stilbene-based compound (1) has been prepared and was highly selective for the detection of cyanide anion in aqueous media even in the presence of other anions, such as F(-), Cl(-), Br(-), I(-), ClO(4)(-), H(2)PO(4)(-), HSO(4)(-), NO(3)(-), and CH(3)CO(2)(-). A noticeable change in the color of the solution, along with a prominent fluorescence enhancement, was observed upon the addition of cyanide. The color change was observed upon the nucleophilic addition of the cyanide anion to the electron-deficient cyanoacrylate group of 1. The spectral changes induced by the reaction were analyzed by comparison with two model compounds, such as compound 2 with dimethyl substituents and compound 3 without a cyanoacrylate group. An intramolecular charge-transfer (ICT) mechanism played a key role in the sensing properties, and the mechanism was supported by DFT/TDDFT calculations.

Synthesis and photovoltaic property of copolymers with phenanthrothiadiazole moiety

A new accepter unit, phenanthro[9,10-c][1,2,5]thiadiazole, was synthesized and utilized for the syntheses of the conjugated polymers containing electron donor–acceptor pairs for OPV devices in order to describe the effect of changing the coupling position with cyclopentadithiophene unit. This novel phenanthro[9,10-c][1,2,5]thiadiazole unit with a phenanthene group possesses an electron deficient thiadiazole group and can promote planarity of the compound. The solid films of PCPDTPTm with meta linkage and PCPDTPTp with para linkage show absorption bands with maximum peaks at about 460 and 484nm and the absorption onsets at 558 and 579nm, corresponding to band gaps of 2.22 and 2.14eV, respectively. The absorption spectrum of the PCPDTPTp was red shifted as compared to that of PCPDTPTm, which reveals that PCPDTPTp has longer conjugated length caused by the coupling position. The electron density of the PCPDTPTm HOMO is distributed not only on the donor moiety but also on the thiadiazole moiety to generate intermolecular charge transfer from cyclopentadithiophene unit to phenanthrothiadiazole unit. The device with PCPDTPTm:PC71BM with TiOx layer showed VOC value of 0.97V, JSC value of 5.50mA/cm2, and FF of 0.33, giving power conversion efficiency of 1.80%.

Practical one-pot preparation of ketones from aryl and alkyl bromides with aldehydes and DIH via Grignard reagents

Various diaryl ketones, alkyl aryl ketones, and dialkyl ketones were efficiently prepared in good yields by the reactions of the Grignard reagents derived from aryl or alkyl bromides, followed by the reactions with aromatic or aliphatic aldehydes and the subsequent treatment with 1,3-diiodo-5,5-dimethylhydantoin and K2CO3, in a one-pot method. The same treatment of aromatic bromides bearing electron-withdrawing groups, such as ester, nitrile, ketone, and nitro groups with i-PrMgCl·LiCl or PhMgCl instead of Mg, also provided the corresponding diaryl and alkyl aryl ketones in good yields. The above methods are simple and practical transition-metal-free methods for the preparation of various diaryl ketones and alkyl aryl ketones bearing electron-rich aromatic groups and electron-deficient aromatic groups, as well as dialkyl ketones.

Ultrafast Infrared and UV–Vis Studies of the Photochemistry of Methoxycarbonylphenyl Azides in Solution

The photochemistry of 4-methoxycarbonylphenyl azide (2a), 2-methoxycarbonylphenyl azide (3a), and 2-methoxy-6-methoxycarbonylphenyl azide (4a) were studied by ultrafast time-resolved infrared (IR) and UV-vis spectroscopies in solution. Singlet nitrenes and ketenimines were observed and characterized for all three azides. Isoxazole species 3g and 4g are generated after photolysis of 3a and 4a, respectively, in acetonitrile. Triplet nitrene 4e formation correlated with the decay of singlet nitrene 4b. The presence of water does not change the chemistry or kinetics of singlet nitrenes 2b and 3b, but leads to protonation of 4b to produce nitrenium ion 4f. Singlet nitrenes 2b and 3b have lifetimes of 2 ns and 400 ps, respectively, in solution at ambient temperature. The singlet nitrene 4b in acetonitrile has a lifetime of about 800 ps, and reacts with water with a rate constant of 1.9 × 10(8) L·mol(-1)·s(-1) at room temperature. These results indicate that a methoxycarbonyl group at either the para or ortho positions has little influence on the ISC rate, but that the presence of a 2-methoxy group dramatically accelerates the ISC rate relative to the unsubstituted phenylnitrene. An ortho-methoxy group highly stabilizes the corresponding nitrenium ion and favors its formation in aqueous solvents. This substituent has little influence on the ring-expansion rate. These results are consistent with theoretical calculations for the various intermediates and their transition states. Cyclization from the nitrene to the azirine intermediate is favored to proceed toward the electron-deficient ester group; however, the higher energy barrier is the ring-opening process, that is, azirine to ketenimine formation, rendering the formation of the ester-ketenimine (4d') to be less favorable than the isomeric MeO-ketenimine (4d).

Side Chain Engineering of Polythiophene Derivatives with a Thienylene–Vinylene Conjugated Side Chain for Application in Polymer Solar Cells

Two new conjugated side-chain isolated polythiophene derivatives, PT4TV and PT4TV-C, were designed and synthesized by copolymerization of thiophene unit with thienylene–vinylene (TV) conjugated side chain and unsubstituted terthiophene unit. The difference of the two polymers is an additional carbonyl group on the conjugated TV side chain in PT4TV-C. Compared to previous reported conjugated side chain polythiophenes (CSC-PTs) with concentrated side chains, PT4TV and PT4TV–C showed red-shifted and enhanced π–π* transition absorption of the polymer backbone along with the shoulder peak and steep absorption edge, indicating ordered polymer main chains and well-packed side chains. PT4TV possessed an absorption edge of 663 nm and a HOMO energy level at −5.21 eV. The introducing of electron deficient carbonyl group in PT4TV–C led to 17 nm red-shifted absorption and a down-shifted HOMO energy level at −5.26 eV, but aroused the issue of poorer planarity of the polymer backbone. The more ordered structure in PT4TV...

Triarylborane-functionalized polynorbornenes: Direct polymerization and signal amplification in fluoride sensing

The vinyl-addition homo- and copolymerization of a norbornene monomer bearing an electron-deficient triarylborane side group (M1) using Pd(II) catalyst in the presence of the 1-octene chain transfer agent efficiently produced a novel class of soluble polynorbornenes functionalized with triarylborane groups. The catalytic system provided high-molecular-weight polymers (Mw > 200 × 103 g/mol) with high thermal stability (Td5 = 240–390 °C) depending on the M1 content. Characterization by multinuclear NMR spectroscopy revealed the formation of vinyl-type polynorbornes with a controlled amount of M1 and the presence of a base-free tricoordinate boron center. While UV–vis absorption and PL spectra of the polymers displayed almost identical absorption and emission features to those of M1, indicating the absence of intramolecular aggregation or excimer formation in both the ground and excited states, the homopolymer showed enhanced fluorescence quenching efficiency in the sensing of fluoride anions in comparison with M1. Moreover, a positive correlation between the fluorescence quenching efficiency and the content of borane moiety in the polymer chain was observed for the polymers.

Electrochemistry: An Efficient Way to Chemically Modify Individual Monolayers of Graphene

Fast and efficient surface functionalization of graphene is achieved by the electrochemical formation of aryl radicals from diazonium salts under mild conditions. Precise control of the ratio of electron-deficient nitro groups to electron-rich amino groups is also demostrated, potentially resulting in the controllable tuning of the electrical properties of graphenes.

Derivatization of Bichromic Cyclometalated Ru(II) Complexes with Hydrophobic Substituents

The syntheses and physical properties of cyclometalated Ru(II) complexes containing a triphenylamine (TPA) unit bearing aliphatic groups are reported. Each member of the series consists of an octahedral Ru(II) center coordinated by a tridentate polypyridyl ligand and a tridentate cyclometalating ligand. One of the chelating ligands contains electron-deficient methyl ester groups, while a TPA unit is attached to the central ring of the adjacent chelating ligand through a thiophene bridge. This study builds on our previous work (Inorg. Chem. 2011, 50, 6019-6028; Inorg. Chem. 2011, 50, 5494-5508) by (i) outlining a synthetic protocol for installing aliphatic groups on the TPA substituents, (ii) examining the role that terminal -O-hexyl and -S-hexyl groups situated on the TPA have on the electrochemical properties, and (iii) demonstrating the potential benefit of installing the TPA on the neutral chelating ligand rather than the anionic chelating ligand. The results reported herein provide important synthetic advances for our broader goal of developing bis-tridentate cyclometalated Ru(II) complexes for light-harvesting applications.

Thiol-Michael coupling chemistry: facile access to a library of functional exo-7-oxanorbornenes and their ring-opening metathesis (co)polymerization

The nucleophile initiated thiol-Michael reaction of a wide range of mono and multifunctional thiols with a novel acrylic exo-7-oxanorbornene is described. We highlight how this process affords ready access to a large library of thioether-based substrates in a quick and convenient fashion. New substrates containing, for example, ester, fluoro, and siloxy functionality polymerized in a controlled fashion with Grubbs' first generation (G1) catalyst, RuCl2(PCy3)2CHPh, yielding homopolymers with controlled, predetermined molecular weights and polydispersity indices in the range 1.10–1.31. Other examples containing –OH (alcohol, diols, sugars) and certain heterocyclic functionality could only be polymerized to high conversion in a controlled manner with the Grubbs' third generation catalyst, RuCl2(3-BrPy)2(ImMesH2)CHPh. Examples of copolymers with statistical and block architectures were also prepared yielding well-defined materials with controlled molecular weights and narrow, unimodal molecular weight distributions. Efficient, sequential post-polymerization modification of an AB diblock copolymer bearing protected alkyne and protected sugar functionality afforded access to additional new block copolymers including amphiphilic species as well as a common material susceptible to Cu(I)-catalyzed alkyne-azide coupling. Finally, we show that the common, and key, acrylic functional exo-7-oxanorbornene substrate can, if desired, be directly (co)polymerized with the Grubbs' G1 catalyst yielding (co)polymers containing electron-deficient ene functional groups that can be modified post-polymerization.

Synthesis and characterization of benzodithiophene–isoindigo polymers for solar cells

Three new alternating polymers with the electron-deficient isoindigo group as the acceptor unit and benzo[1,2-b:4,5-b′]dithiophene (BDT) or BDT flanked by thiophenes (or octylthiophenes) as the donor unit were designed and synthesized. All the polymers have good thermal stability, solubility and broad absorption spectra. Their photophysical, electrochemical and photovoltaic (PV) properties were investigated. To understand their different PV performance in the resulting polymer solar cells (PSCs), the morphology of their blends with fullerene derivatives was investigated by atomic force microscopy, and the molecular geometries as well as the molecular frontier orbitals were simulated by density functional theory calculations (Gaussian 09). The polymer PBDT-TIT, with BDT flanked by thiophenes as the donor unit and isoindigo as the acceptor unit, exhibits quite planar backbones and its blend with fullerene derivatives shows optimal morphology. As a result, the PSCs based on PBDT-TIT with a conventional device configuration of ITO/PEDOT:PSS/PBDT-TIT:PC61BM/LiF/Al showed a power conversion efficiency of 4.22%, with a short-circuit current density of 7.87 mA cm−2, an open-circuit voltage of 0.79 V and a fill factor of 0.68 under the AM 1.5G illumination with an intensity of 100 mW cm−2 from a solar simulator.

Theory Design of Two Polymer Donors for Organic Heterojunction Solar Cells

A highly efficient organic solar cell needs a copolymer as donor possessing low-band gap, high open-circuit voltage (Voc), good charge transfer at donor-acceptor (D-A) interface, and good transport properties in polymers. As the first step towards this goal, we constructed two polymers (PBnDT-HTAZ and PBnDT-6CNTAZ) incorporating benzodithiophene (BnDT) as the electron-rich units and either 1H-benzo(d)(1,2,3)triazole (HTAZ) or 1H-benzo(d)(1,2,3)triazole-6-carbonitrile (6CNTAZ) as the electron-deficient unit. The designed PBnDT-6CNTAZ was introduced a cyano in the electron-deficient unit. PBnDT-HTAZ and PBnDT-6CNTAZ as donors and (6,6)-phenyl C61-butyric acid methyl ester (PC60BM) as an ac- ceptor in hetero-organic solar cell, as well as the D-A complexes are investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) in this work. The electronic properties, optical absorption properties, intramolecular and intermolecular charge transfer, exciton binding energy of two polymers and corresponding D-A com- plexes are discussed. By means of Marcus theory, the exciton-dissociation, charge-recombination rate of D-A complex at the D-A interface, and the hole-transport rate of polymer donors are studied. According to the computational results, it indicates that the two polymers have strong and wide absorption peaks in visible region, as well as strong intramolecular charge trans- fer and intermolecular charge transfer for corresponding D-A complex. The designed PBnDT-6CNTAZ possesses lower the energy of the highest occupied molecular orbital (HOMO) so that PBnDT-6CNTAZ exhibits larger open-circuit voltage and better ability of antioxidant in comparison with PBnDT-HTAZ. The two polymers corresponding D-A complexes have small exciton binding energy. The PBnDT-6CNTAZ has good ability of charge transfer and larger hole-transport rate in compari- son to PBnDT-HTAZ. It is thus clear that incorporating cyano in polymer (PBnDT-6CNTAZ) have an important impact on performance of organic solar cell. Therefore, we can infer that PBnDT-6CNTAZ may be a potential donor material of bulk heterojunction solar cells. The present calculated results demonstrated a first attempt of providing a theoretical model for the introduction of electron-deficient groups in copolymer donors. These results may provide a structural guideline for optimiz- ing chemical construction of copolymer donors to improve the performance of bulk heterojunction solar cells. Our computa- tional models and conclusions can be applied to design and predict other new polymer donors. Keywords organic solar cell; donor-acceptor complex; benzotriazole; charge transfer

Structures and properties of conjugated Donor–Acceptor copolymers for solar cell applications

With the rapid evolution of photovoltaic polymer materials, power conversion efficiency of polymer solar cells has been markedly improved in recent years, and is now approaching a landmark value of 10 %. This review focuses on Donor–Acceptor (D–A) photovoltaic copolymers. Starting from briefly introducing the D–A concept, the fundamental donor and acceptor units for constructing polymer photovoltaic materials are introduced and classified. By summarizing the structure–property relationships of typical photovoltaic D–A copolymers, the important design rules for such materials are highlighted. Several crucial aspects, including proper combination of D–A units, high planarity of the backbone and proper incorporation of side chains are particularly emphasized. A new D–A architecture, namely main-chain donor and side-chain acceptor is introduced and reviewed. Moreover, the role of the electron-deficient group in fine-tuning energy levels of low-bandgap D–A photovoltaic polymers is discussed.

Free terminal amines in DNA-binding peptides alter the product distribution from guanine radicals produced by single electron oxidation

Purpose: Electron deficient guanine radical species are major intermediates produced in DNA by the direct effect of ionizing irradiation. There is evidence that they react with amine groups in closely bound ligands to form covalent crosslinks. Crosslink formation is very poorly characterized in terms of quantitative rate and yield data. We sought to address this issue by using oligo-arginine ligands to model the close association of DNA and its binding proteins in chromatin.Materials and methods: Guanine radicals were prepared in plasmid DNA by single electron oxidation. The product distribution derived from them was assayed by strand break formation after four different post-irradiation incubations.Results: We compared the yields of DNA damage produced in the presence of four ligands in which neither, one, or both of the amino and carboxylate termini were blocked with amides. Free carboxylate groups were unreactive. Significantly higher yields of heat labile sites were observed when the amino terminus was unblocked. The rate of the reaction was characterized by diluting the unblocked amino group with its amide blocked derivative.Conclusion: These observations provide a means to develop quantitative estimates for the yields in which these labile sites are formed in chromatin by exposure to ionizing irradiation.

Nine in a Row: Taming the Acenes

Stabilization of higher acenes represents a notoriously challenging task. The synthesis developed here takes advantage of the concomitant beneficial effects of silylethyne substituents and electron-deficient phenyl groups. Further, fluorinated extremities are believed to enhance stability and π-stacking interactions. Products 1-3 are isolated as crystalline compounds, suitable for X-ray diffraction analysis. Moreover, solutions are stable enough to allow electrochemical and photophysical measurements to be performed.

Developing Visible Fluorogenic ‘Click-On’ Dyes for Cellular Imaging

New fluorogenic dyes were designed and synthesized based on Cu(I)-catalyzed 'click' reaction. Conjugating weakly fluorescent benzothiazole derivatives with an electron-deficient alkyne group at the 2-position with azide-containing molecules in aqueous solution form 'click-on' fluorescent adducts. Model reactions and cell culture experiment indicated that the developed 'click-on' dye could be applied to labeling various biomolecules, such as nucleic acids, proteins, and other molecules, in cells.

Iodocyclization of N-Aryl-3-phenylpropiolamides by I2/CAN: A Convenient Route for the Selective Synthesis of Quinolin-2-ones

A general method has been developed for the selective synthesisof 3-iodoquinolin-2-ones and spiro[4.5]trienesvia intramolecular iodocyclization of N-( ORTHO-substituted aryl)-3-phenylpropiolamidesusing iodine/cerium(IV) ammonium nitrate reagent undermild reaction conditions. The electronic effect of ORTHO-substituents(electron-rich and electron-deficient group) triggers the two differentreaction pathways resulting to iodocyclized quinolin-2-one and IPSO-iodocyclized spiro-type compounds.

Non-redox Oxy-Insertion via Organometallic Baeyer–Villiger Transformations: A Computational Hammett Study of Platinum(II) Complexes

A Hammett analysis of platinum-mediated oxy-insertion into Pt–aryl bonds is performed using DFT calculations. Modeled transformations involve the conversion of cationic PtII-aryl complexes [(Xbpy)Pt(R)(OY)]+ (R = p-X-C6H4; Y = 4-X-pyridine; Xbpy = 4,4′-X-bpy; X = NO2, H, NMe2) to the corresponding [(Xbpy)Pt(OR)]+ complexes via an organometallic Baeyer–Villiger (BV) pathway. Computational modeling predicts that incorporation of an electron-deficient NO2 group at the 4-position of pyridine-N-oxide lowers the activation barrier to the organometallic BV transformation. In contrast, computational studies reveal that increasing the donor ability of the migrating aryl group, by placement of NMe2 at the para position, lowers the activation barrier to the oxy-insertion step. The impact on the calculated activation barrier is greater for variation of the R group than for modification of Y of the oxygen delivery reagent. For the p-NO2/p-NMe2-substituted aryl migrating groups (R), the ΔΔG‡ for X = NMe2 versus X = NO2...

Quantum-Chemical Calculations and IR Spectra of the (F2)MF2 Molecules (M = B, Al, Ga, In, Tl) in Solid Matrices: A New Class of Very High Electron Affinity Neutral Molecules

Electron-deficient group 13 metals react with F(2) to give the compounds MF(2) (M = B, Al, Ga, In, Tl), which combine with F(2) to form a new class of very high electron affinity neutral molecules, (F(2))MF(2), in solid argon and neon. These (F(2))MF(2) fluorine metal difluoride molecules were identified through matrix IR spectra containing new antisymmetric and symmetric M-F stretching modes. The assignments were confirmed through close comparisons with frequency calculations using DFT methods, which were calibrated against the MF(3) molecules observed in all of the spectra. Electron affinities calculated at the CCSD(T) level fall between 7.0 and 7.8 eV, which are in the range of the highest known electron affinities.

Development of a new conjugated polymer containing dialkoxynaphthalene for efficient polymer solar cells and organic thin film transistors

AbstractA new semiconducting polymer, poly((5,5‐E‐α‐((2‐thienyl)methylene)‐2‐thiopheneacetonitrile)‐alt‐2,6‐[(1,5‐didecyloxy)naphthalene])) (PBTADN), an alternating copolymer of 2,3‐bis‐(thiophene‐2‐yl)‐acrylronitrile and didecyloxy naphthalene, is synthesized and used as an active material for organic thin film transistors (OTFTs) and organic solar cells. The incorporation of 2,3‐bis‐(thiophene‐2‐yl)‐acrylronitrile as an electron deficient group and didecyloxy naphthalene as an electron rich group resulted in a relatively low bandgap, high charge carrier mobility, and finally good photovoltaic performances of PBTADN solar cells. Because of the excellent miscibility of PBTADN and PC71BM, as confirmed by Grazing Incident X‐ray Scattering (GIXS) measurements and Transmission Electron Microscopy (TEM), homogeneous film morphology was achieved. The maximum power conversion efficiency of the PBTADN:PC71BM solar cell reached 2.9% with a Voc of 0.88 V, a short circuit current density (Jsc) of 5.6 mA/cm2, and a fill factor of 59.1%. The solution processed thin film transistor with PBTADN revealed a highest saturation mobility of 0.025 cm2/Vs with an on/off ratio of 104. The molecular weight dependence of the morphology, charge carrier mobility, and finally the photovoltaic performances were also studied and it was found that high molecular weight PBTADN has better self assembly characteristics, showing enhanced performance. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Development of benzothiazole ‘click-on’ fluorogenic dyes

‘Click-on’ fluorogenic reaction: a non-fluorescent benzothiazole with an electron-deficient alkyne group at 2-position reacts with azide containing molecules could form fluorescent adducts.