Electron-deficient Groups Research Articles

Charge transfer and first hyperpolarizability: cage-like radicals C59X and lithium encapsulated Li@C59X (X=B, N).

Very recently, two new cage-like radicals (C59B and C59N) formed by a boron or nitrogen atom substituting one carbon atom of C60 were synthesized and characterized. In order to explore the structure-property relationships of combination the cage-like radical and alkali metal, the endohedral Li@C59B and Li@C59N are designed by lithium (Li) atom encapsulated into the cage-like radicals C59B and C59N. Further, the structures, natural bond orbital (NBO) charges, and nonlinear optical (NLO) responses of C59B, C59N, Li@C59B, and Li@C59N were investigated by quantum chemical method. Three density functional methods (BHandHLYP, CAM-B3LYP, and M05-2X) were employed to estimate their first hyperpolarizabilities (β tot) and obtained the same trend in the β tot value. The β tot values by BHandHLYP functional of the pure cage-like radicals C59B (1.30 × 10(3) au) and C59N (1.70 × 10(3) au) are close to each other. Interestingly, when one Li atom encapsulated into the electron-rich radical C59N, the β tot value of the Li@C59N increases to 2.46 × 10(3) au. However, when one Li atom encapsulated into the electron-deficient radical C59B, the β tot value of the Li@C59B sharply decreases to 1.54 × 10(2) au. The natural bond orbital analysis indicates that the encapsulated Li atom leads to an obvious charge transfer and valence electrons distribution plays a significant role in the β tot value. Further, frontier molecular orbital explains that the interesting charge transfer between the encapsulated Li atom and cage-like radicals (C59B and C59N) leads to differences in the β tot value. It is our expectation that this work will provide useful information for the design of high-performance NLO materials.

A ratiometric chemodosimeter for highly selective naked-eye and fluorogenic detection of cyanide

A simple indole-based chemosensor (1) with a very low molecular weight of 207 g mol−1 has been synthesized for the highly reactive and selective detection of CN− in aqueous media, even in the presence of other anions, such as F−, Cl−, Br−, AcO−, S2−, SCN−, NO2−, NO3−, CO3−, BzO−, H2PO4−, and HSO4−. The sensor achieves rapid detection of cyanide anion in 2 min, and the pseudo-first-order rate constant is estimated as 1.576 min−1. The colorimetric and ratiometric fluorescent response of the sensor to CN− is attributable to the addition of CN− to the electron-deficient dicyanovinyl group of 1, which prevents intramolecular charge transfer. The sensing mechanism is supported by density functional theory and time-dependent density functional theory calculations. Moreover, sensor 1 exhibits both high accuracy in determining the concentration of CN− in real samples and 1-based test strips can conveniently detect CN− without any additional equipment. The detection limit of the sensor 1 (1.1 μM) for cyanide is lower than the maximum permissible level of CN− (1.9 μM) in drinking water.

Pyrrolyl-Silicon Compounds as Precursors for Donor-Acceptor Systems Stabilized by Noncovalent Interactions.

Pyrrolyl-silicon compounds were investigated by different theoretical approaches. Model monomers consisted of a pyrrole ring N-substituted with silylmethoxy and silylhydroxy end groups through a propyl chain spacer, designated as PySi and PySiOH. Geometrical, vibrational, and electronic properties, as well as chemical reactivity, are discussed and compared with pyrrole (Py) and N-propylpyrrole (N-PrPy) that were studied in parallel for reference purposes and methods validation. The electronic distribution between PySi and PySiOH differs importantly, the former being an electron donor, as Py and N-PrPy. Conversely, PySiOH presents donor-acceptor character with the LUMO energy level localized on the silanol end group. Global and local reactivity descriptors predict PySiOH more reactive than PySi with two preferential reactive sites: electron-rich Py ring and electron-deficient silanol group. On the basis of experimental studies, oligomers of PySiOH linked α-α' via Py rings (α-α'PynSiOH, n = 2, 3) were considered as model molecules of hydrolyzed PySi. The most stable structures were derived from randomly generated α-α'PynSiOH that were optimized at semiempirical AM1 and refined with M05-2X/6-31G(d,p). Conformational analysis of dimer and trimer structures points to stability enhanced by molecular packing. Nonetheless, NBO and RDG results indicate that oligomer stability is dictated by the cooperative contribution of hydrogen bonding between silanol end groups and dispersive vdW interactions between silanol and the π system of the Py ring. The latter interaction resulting from electron delocalization induced by an electron-deficient silanol group seems to determine the smaller gap energy of T-shaped OH-π arrangements. The theoretical findings support the peculiar chemical behavior revealed by experiment.

Aldehyde end-capped terthiophene with aggregation-induced emission characteristics

From the viewpoint of practical application, organic materials that are emissive in aggregate or solid state have been a hot research topic. This work demonstrates that 2,2′:5′,2″-terthiophene-5-carbaldehyde (TTA) exhibited aggregation-induced emission (AIE) property. The photophysical properties of the aldehyde in THF/H2O mixtures were studied, and the aggregates formed with different water fractions were studied by scanning electron microscopy. Our results indicated that the presence of an electron deficient aldehyde group as the end-capped group should endow TTA with AIE characteristic. Furthermore, ordered nanoscale aggregates of TTA exhibited distinct AIE behavior when assembled in solutions with appropriate water content.

Boronic Acid Functionalized Aza-Bodipy (azaBDPBA) based Fluorescence Optodes for the Analysis of Glucose in Whole Blood.

A near-infrared fluorescent dye (aza-bodipy or azaBDPBA) functionalized with boronic acid groups was synthesized for the preparation of optodes to measure glucose in 40-fold diluted whole blood. Boronic acid groups as an electron deficient group on aza-bodipy was reacted with hydrogen peroxide into an electron-rich phenolic group leading to the red-shift of emission wavelength from 682 to 724 nm. The emission in near-infrared region offered a low level of background interference from whole blood. Also, the dual-wavelength emission guaranteed our probe to measure glucose in whole blood accurately after the conversion of glucose into hydrogen peroxide using glucose oxidase. The measuring range of glucose from 0.2 to 200 mM in the buffer was achieved with high selectivity. To facilitate the blood test, the probe was immobilized into thin hydrophobic polymer films to prepare the disposal glucose optode, which could detect glucose in the solution from 60 μM to 100 mM. The concentration of glucose in 40-fold diluted whole blood was determined using our optode and the reference method, respectively. The consistence in the concentration obtained from these two assays revealed that our azaBDPBA-based optodes were promising for the clinic assay of glucose in the whole blood.

Polyaniline-based photothermal paper sensor for sensitive and selective detection of 2,4,6-trinitrotoluene.

We report for the first time a photothermal paper sensor for the selective and sensitive detection of 2,4,6-trinitrotoluene (TNT) down to 14 ng/cm(2). In the presence of TNT, a Meisenheimer complex was formed by means of a charge transfer process from an electron-rich group in polyaniline (PANI) to an electron-deficient nitro group in TNT, which resulted in the near-infrared absorption around 800 nm. Upon irradiation with an 808 nm diode laser, the photothermal effect of the PANI/TNT complex caused the temperature increase, and the temperature difference (ΔT) was proportional to the TNT concentration, while the temperature increase was hardly observed for other nitroaromatics including 2,4-dinitrotoluene (DNT), 2,4,6-trinitrophenol (TNP), and nitrobenzene (NB), affording high selectivity toward TNT. All the tests can be conducted both in solution and on paper. Therefore, the proposed photothermal strategy not only offers a fast and convenient protocol for selective detection of TNT but also indicates great potential in practical applications, especially for airport/railway security inspection and prevention of terrorist attacks.

Asymmetric 1,2-perfluoroalkyl migration: easy access to enantioenriched α-hydroxy-α-perfluoroalkyl esters.

This study has led to the development of a novel, highly efficient, 1,2-perfluoro-alkyl/-aryl migration process in reactions of hydrate of 1-perfluoro-alkyl/-aryl-1,2-diketones with alcohols, which are promoted by a Zn(II)/bisoxazoline and form α-perfluoro-alkyl/-aryl-substituted α-hydroxy esters. With (-)-8-phenylmenthol as the alcohol, the corresponding menthol esters are generated in high yields with excellent levels of diastereoselectivity. The mechanistic studies show that the benzilic ester-type rearrangement reaction takes place via an unusual 1,2-migration of electron-deficient trifluoromethyl group rather than the phenyl group. The overall process serves as a novel, efficient, and simple approach for the synthesis of highly enantioenriched, biologically relevant α-hydroxy-α-perfluoroalkyl carboxylic acid derivatives.

Effect of the π Bridge and Acceptor on Intramolecular Charge Transfer in Push-Pull Cationic Chromophores: An Ultrafast Spectroscopic and TD-DFT Computational Study.

Three (donor-π-acceptor)(+) systems with a methyl pyridinium or quinolinium as the electron-deficient group, a dimethyl amino as the electron-donor group, and an ethylene or butadiene group as the spacer have been investigated in a joint spectroscopic and TD-DFT computational study. A negative solvatochromism has been revealed in the absorption spectra, which implies a solution color change, and interpreted by considering the variation in the permanent dipole moment modulus and orientation upon photoexcitation. The fluorescence efficiency decreases upon increasing solvent polarity, in agreement with the excited-state optimized geometries (planar in low-polarity media and twisted in high-polarity media). Femtosecond transient absorption has revealed the occurrence of a fast photoinduced intramolecular charge transfer (ICT) and the molecular factors that determine an efficient ICT. Considering the crucial role of the ICT in tuning the nonlinear optical (NLO) properties, these compounds can be considered promising NLO materials.

Ruthenium sensitizers with various 2-thiophenimidazo[4,5-f][1,10]phenanthroline based ancillary ligands and their performance for dye-sensitized solar cells

This paper reports four new ruthenium sensitizers (S1–S4) for the studies on dye-sensitized solar cells. The four ruthenium sensitizers have been synthesized via a step-by-step synthetic strategy via their respective precursors (D1–D4), where 2-thiophenimidazo[4,5-f][1,10]phenanthroline based ancillary ligands are present with different substituents at α and β positions of the thiophene unit. It is found that the introduction of an electron-deficient radical at β positions of the thiophene unit in the ancillary ligand has a positive influence on the efficiency of the final dye-sensitized solar cells, where sensitizer S3 shows the best overall power-conversion efficiencies in this group of ruthenium sensitizers (4.95% compared to 6.07% for sensitizer N3). In addition, three single-crystal structures of organometallic precursors (D1–D3) are included, which are the first structural examples on Ru(II) complexes containing p-cymene and TIP based ligands simultaneously.

Molecular design and theoretical investigation on the thieno[3,2-b]thienobis(silolothiophene)-based low band gap donor polymers for efficient polymer solar cell

Donor–acceptor (D–A) copolymers have been proved to be excellent candidates for efficient polymer solar cells. In this paper, a series of D–A polymers with the same donor unit of Si4T and different acceptor units are theoretically designed. Two novel strategies (extending the length of π-conjugation and using the electron-deficient groups) have been considered for the conjugated polymer design. The energy levels and band gaps are theoretically investigated using the confirmed density functional theory/time-dependent density functional theory method. The results show that, compared with two original polymers, the newly designed D–A polymers have better predicted performances with smaller band gaps and lower highest occupied molecular orbital energy levels. When combined with fullerene derivatives (PCBM) for organic solar cells, these polymers can produce power conversion efficiencies as high as ∼10%, estimated by Scharber diagrams.

ChemInform Abstract: Copper‐Catalyzed N‐Arylation of 2‐Arylindoles with Aryl Halides.

Abstract 10 mol% CuI combined with the DMEDA ligand can efficiently catalyze the N -arylation of 2-arylindoles with aryl iodides and aryl bromides in good to excellent yields. The aryl halides bearing electron-rich or electron-deficient functional groups can be well tolerated under this mild reaction conditions.

The position effect of electron-deficient quinoxaline moiety in porphyrin based sensitizers

An electron-deficient group, 2,3-diphenylquinoxaline (DPQ), is incorporated as an auxiliary acceptor into the different positions of the porphyrin (Por) based donor-π bridge-acceptor (D-π-A) dye (FNE57) to construct D-A′-Por-π-A (FNE58) and D-Por-A′-π-A (FNE59) configurations. The incorporation of DPQ unit between the donor and porphyrin unit has negligible influence on the absorption property, whereas the DPQ unit located between the porphyrin unit and acceptor significantly increases the absorbance for the Soret band and the valley between the Soret and Q bands. Theoretical calculation reveals that incorporating the DPQ unit adjacent to the acceptor is more advantageous to delocalize the lowest unoccupied molecular orbital and enhance the electronic asymmetry, which facilitates the intramolecular charge transfer. The effect of DPQ unit and its linkage position on the performance of related quasi-solid-state dye-sensitized solar cells (DSSCs) is systematically investigated. The quasi-solid-state DSSC with sensitizer FNE59 displays a power conversion efficiency of 6.02%, which is 23% and 51% higher than those for FNE57 and FNE58 based DSSCs. Our studies facilitate the understanding of the crucial importance of molecular engineering and pave a new path to design novel porphyrin based sensitizers for highly efficient DSSCs.

Mechanism of Selective C–H Hydroxylation Mediated by Manganese Aminopyridine Enzyme Models

The mechanism of selective oxidation of aliphatic C–H groups with H2O2 in the presence of aminopyridine Mn complexes, modeling the reactivities of natural oxygenases of the cytochrome P450 superfamily, has been examined. The oxygenation of C–H groups proceeds via hydrogen atom abstraction by the electrophilic metal site; the logarithm of C–H oxidation rates correlates linearly with bond dissociation energies for homolytic C–H bond cleavage. Hammett correlations and stereospecificity studies reflect the formation of a short-lived electron-deficient radical intermediate. Isotopic labeling studies confirm the incorporation of 18O from added H218O, thus providing so far lacking evidence for the oxomanganese(V)-mediated oxidation mechanism.

Efficient Aerobic Oxidative Synthesis of Benzimidazoles with Fe(III) based PEG1000 Dicationic Imidazolium Ionic Liquid/toluene Temperature‐dependent Biphasic System

AbstractA green protocol for the synthesis of benzimidazoles with Fe(III) based PEG1000 dicationic imidazolium ionic liquid ([PEG1000mim2][FeCl4]2)/toluene temperature‐dependent biphasic system was described. Conformed by IR analysis, FeCl4− is the dominating anion species. It could be seen that aldehydes aryla mines and aromatic aldehydes bearing electron‐deficient group (Cl, Br, NO2) and electron‐rich groups (OH, N(CH3)2) on the aromatic rings gave good yields (78–96 %). Moreover, the Fe(III) based PEG1000 dicationic imidazolium ionic liquid could be recycled and reused without significant loss of catalytic activity after seven runs.

A new conjugated polymer PPV-PCN: synthesis, characterization, and applications

A new conjugated polymer PPV-PCN containing alternating alkoxy-substituted aromatic and cyano-substituted aromatic units was synthesized and characterized by NMR, FIR, GPC and TGA. The UV–vis absorption spectra and photoluminescence emission spectra in solution/films were characterized. The results indicate PPV-PCN has a smaller optical band gap value (2.05 eV) compared to homopolymer MEH-PPV, it is ascribed to PPV-PCN with structure of alternative electron-rich alkoxy substituted aromatic and electron-deficient cyano group along conjugated backbone. Its photoinduced charge transfer application in trinitrotoluene (TNT) detection was studied, and the results show that this polymer can be a potential material for detecting TNT in solution. Two types of cells, including inverted-type and conventional-type were studied for PSCs application as well, and the results indicate that the inverted-type device demonstrates better long-term ambient stability as compared to the conventional device and achieves 0.91 % power conversion efficiency finally

Synthesis by Direct Arylation of Thiazole–Derivatives: Regioisomer Configurations–Optical Properties Relationship Investigation

The synthesis of thiazole(Tz)-based regioisomer materials using selective direct arylation to avoid any protection steps has been developed. A series of trimers in which the Tz groups sandwich either an electron-rich or an electron-deficient unit, with a regioselective orientation of the respective Tz unit, has therefore been synthesized. This chemical strategy has also been followed to synthesize a second series of pentamers in which the Tz group is used as a π-conjugated bridge between an electron-rich central unit and electron-deficient end-capping groups and vice versa. On both trimers and pentamers, the effect of Tz orientation on the conjugation properties of the synthesized materials was investigated by a combination of experimental measurements and density functional theory calculations. This study highlights that control of the orientation of the Tz unit leads to the synthesis of the most conjugated regioisomer derivative. The present work gives chemical synthesis tools for the synthesis of selectively oriented Tz-based materials as well as a general guideline for the design of Tz-based materials with the highest conjugation length, including the Tz-orientation effect.

Diarylureas as allosteric modulators of the cannabinoid CB1 receptor: structure-activity relationship studies on 1-(4-chlorophenyl)-3-{3-[6-(pyrrolidin-1-yl)pyridin-2-yl]phenyl}urea (PSNCBAM-1).

The recent discovery of allosteric modulators of the CB1 receptor including PSNCBAM-1 (4) has generated significant interest in CB1 receptor allosteric modulation. Here in the first SAR study on 4, we have designed and synthesized a series of analogs focusing on modifications at two positions. Pharmacological evaluation in calcium mobilization and binding assays revealed the importance of alkyl substitution at the 2-aminopyridine moiety and electron deficient aromatic groups at the 4-chlorophenyl position for activity at the CB1 receptor, resulting in several analogs with comparable potency to 4. These compounds increased the specific binding of [3H]CP55,940, in agreement with previous reports. Importantly, 4 and two analogs dose-dependently reduced the Emax of the agonist curve in the CB1 calcium mobilization assays, confirming their negative allosteric modulator characteristics. Given the side effects associated with CB1 receptor orthosteric antagonists, negative allosteric modulators provide an alternative approach to modulate the pharmacologically important CB1 receptor.

Surface Chemistry of GaAs(100) and InAs(100) Etching with Tartaric Acid

Incorporating substrates with higher charge mobilities than Si and Ge in metal-oxide-semiconductor field-effect transistors (MOSFETs) would extend the scaling of this device architecture. III-V semiconductors are candidates, and etching and passivation processes are needed that are selective and yield smooth surfaces. The (100) face of III-V compounds contains both electron-deficient group III (Ga, In) atoms and electron-rich group V (P, As, Sb) atoms. Etching InP(100) in a mixture of HCl and H2O2 chlorinates the In (group III) atom forming a soluble product [1,2], yet the P (group V) atom is more reactive and is depleted from the surface [3]. α-Hydroxy acids (lactic, citric, malic, and tartaric) have been shown to bind to the group III atom [3] and could promote more uniform etching. This paper compares the surface chemistry of GaAs and InAs after etching in HCl and H2O2 mixtures with and without tartaric acid.

Design and synthesis of star-burst triphenyamine-based π-conjugated molecules

A series of star-shaped π-conjugated molecules with triphenylamine as the core and a thiophene unit as the π-bridge were designed and synthesized based on a donor-π-bridge-acceptor type of molecular framework. Various peripheral electron-deficient groups including octyl-2-cyanoacrylate, octyl-2,3-dicyanoacrylate and 1,3-diethyl-2-thiobarbituric were incorporated as electron-withdrawing moieties. By altering the terminal groups, star-shaped molecules with symmetric and asymmetric architectures were obtained. It was worth noting that the asymmetric molecules exhibited well-extended absorbance with the combination of absorption features of different donor-acceptor species. Electrochemical investigation indicated that the frontier molecular orbital energy levels can be modified by the terminal electron-withdrawing groups. Despite the fabricated organic photovoltaic devices based on the new molecules as electron-donating materials exhibited less pronounced performances, we surmise the current work illustrated an effective molecular design strategy for the realization of broad absorbance that was beneficial for the utilization of solar photon flux.

Synthetic route to soluble sulfonated poly(arylene sulfone imide)

A target polymer was synthesized by the oxidation of a poly(arylene sulfide imide), which was readily synthesized by the conventional synthetic route for polyimides. A synthetic route to high-molecular-weight sulfonated poly(arylene sulfone imide), which cannot be prepared via the direct synthesis of a polyimide moiety due to the presence of electron-deficient groups in the monomers, has been developed.