Electron-deficient Groups Research Articles

Nucleophilic Ring Opening of Donor-Acceptor Cyclopropanes Catalyzed by a Brønsted Acid in Hexafluoroisopropanol.

A general, Brønsted acid catalyzed method for the room temperature, nucleophilic ring opening of donor-acceptor cyclopropanes in fluorinated alcohol solvent, HFIP, is described. Salient features of this method include an expanded cyclopropane scope, including those bearing single keto-acceptor groups and those bearing electron-deficient aryl groups. Notably, the catalytic system proved amenable to a wide range of nucleophiles including arenes, indoles, azides, diketones, and alcohols.

Efficient synthesis of esters through oxone-catalyzed dehydrogenation of carboxylic acids and alcohols.

Since esters are important organic synthesis intermediates, an environmentally friendly oxone catalyzed-esterification of carboxylic acids with alcohols has been developed. A series of carboxylic acid esters are obtained in high yield. This strategy requires mild reaction conditions, providing an attractive alternative for the construction of valuable carbonyl esters. Electron-rich and electron-deficient groups are compatible with the standard conditions and a variety of substrates are demonstrated. Moreover, the reaction could easily be adapted to typical prodrugs, drugs and gram-scale synthesis.

Ratiometric fluorescence probe for hydrazine vapor detection and biological imaging.

Hydrazine (N2H4) has been widely applied in most of the chemical industry; however, it is now believed that it can cause serious damage to protein and nucleic acid upon ingestion. Herein we introduced a specially designed molecular probe 1, with an electron deficient lactone group as a specially designed reactive site and a naphthalimide fluorophore that is easily modified owing to lactone involvement. The free probe 1 exhibited blue fluorescence in neutral buffer owing to the low favorability of ICT (intramolecular charge transfer), while the specially designed lactone group could potentially undergo a ring-opening reaction with hydrazine, resulting in a favoured ICT effect and bathochromically shifted (125 nm) fluorescence response. The ratiometric fluorescence signal enabled quantitative determination of hydrazine using probe 1 in complex applications. Besides, probe 1 features a rapid signal response time (within 5 min) and low detection limit (36 nM) for hydrazine. Utilizing these excellent properties, probe 1 was further applied in hydrazine vapor detection and bio-imaging. Conceptually, we now present a new approach for the detection of hydrazine, and the enhanced performances of probe 1 will promote its applications in living systems and the environment.

Influence of the catalyst structure in the cycloaddition of isocyanates to oxiranes promoted by tetraarylstibonium cations.

In the context of our work on electron deficient group 15 cations as Lewis acid catalysts, we have synthesized the triflate salts of a series of tetraarylstibonium cations of general formula [ArSbPh3]+ with Ar = Mes (4+), o-(dimethylamino)phenyl (5+), and o-((dimethylamino)methyl)phenyl (6+). These new cationic antimony derivatives, along with the known [Ph4Sb]+ (1+), 1-naphthyltriphenylstibonium (2+), and [(Ant)SbPh3]+ (3+), have been evaluated as catalysts for the cycloaddition of oxiranes and isocyanates under mild conditions. While all stibonium cations favor the 3,4-oxazolidinone products, the reactivities of 5+ and 6+ are hindered by the ancillary amino donor which quenches the Lewis acidity of the antimony center. A comparison of the other stibonium cations shows that 4+ is the most selective catalyst.

Energy levels modulation of small molecule acceptors for polymer solar cells

Non-fullerene acceptor exhibits very promising prospect for the development of polymer solar cells (PSCs). It is necessary to carefully investigate the energy level matching between donor and acceptor to optimize the photovoltaic performance. In this paper, we have designed and synthesized two novel planar A-D-A type small molecular acceptors of IDT-RCN and IDT-CA with 2-(1,1-dicyanomethylene)rhodanine and cyanoacetate as the end groups, respectively. Compared to IDT-RCN with stronger electron-deficient end group, IDT-CA displayed 0.15 eV increase in LUMO level while almost the same HOMO level. PSC devices based on P3HT:IDT-CA show a power conversion efficiency (PCE) of 4.19% with VOC of 0.84 V, JSC of 7.77 mA cm−2 and FF of 0.64, which is much higher than that of P3HT:IDT-RCN mainly due to the higher VOC value. This work indicates that end group modification is important for the modulation of PSC device parameters.

High-performance organic solar cells based on a small molecule with thieno[3,2-b]thiophene as π-bridge

Abstract Herein, we synthesized a new acceptor-π-donor-π-acceptor (A-π-D-π-A) type small molecule donor material BTTR based on thienyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT-T) as the electron-donating core, thieno[3,2-b]thiophene (TT) along with two thiophene units as the π-bridge, and 3-ethylrhodanine (TR) as the electron-deficient end group. The optical, electrical, thermal properties and photovoltaic performance were investigated. BTTR shows strong absorption in the range of 300–700 nm, deep-lying HOMO energy level of −5.32 eV and high hole mobility of 1.01 × 10−3 cm2 V−1 s−1. The organic solar cells (OSCs) based on BTTR:PC71BM (1:0.8, w/w) blend with tetrahydrofuran (THF) solvent vapor annealing (SVA) exhibited an optimized power conversion efficiency (PCE) of 8.0% with an open circuit voltage (Voc) of 0.93 V, a short circuit current density (Jsc) of 13.2 mA cm−2, and a fill factor (FF) of 65.4% under the illumination of AM 1.5G, 100 mW cm−2. The good photovoltaic performance indicates BTTR could be a promising donor material in solution-processed OSCs.

Stereoselective green synthesis and molecular structures of highly functionalized spirooxindole-pyrrolidine hybrids – A combined experimental and theoretical investigation

Highly functionalized spirooxindole-pyrrolidine hybrids have been synthesized stereoselectively through a [3 + 2] cycloaddition strategy in an ionic liquid, 1-butyl-3-methylimidazolium bromide ([bmim]Br). The structure of these spiro heterocyclic hybrids was elucidated using one and two dimensional NMR spectroscopy, single crystal X-ray crystallographic studies and Density Functional Theory (DFT) calculations. The calculated geometric parameters are in good agreement with the experimental data obtained from the X-ray structures. The Natural Bond Orbital (NBO) calculations on these molecules confirm the electron rich carbonyl oxygen and electron deficient NH groups. The 1H and 13C NMR chemical shifts calculated using GIAO method are in good agreement with the experimental data. The DFT computed polarizability values also suggest the possible NLO activity of these molecules.

The Phosphinoboration of N‐Heterocycles

The addition of phosphinoboronate ester Ph2 PBpin (pin=1,2-O2 C2 Me4 ) (1) to a number of different N-heterocycles has been investigated. Reaction of 1 with pyridine resulted in highly selective formation of the corresponding 1,4-addition product, with addition of the electron-deficient Bpin group to the pyridine nitrogen atom and the phosphido group to the para carbon atom. Conversely, reactions of para-substituted pyridine derivatives occurred predominately to afford 1,2-addition products while quinoline reacted to afford the 1,2-adduct which ultimately isomerized to afford the corresponding 1,4-addition product. Preliminary computational studies have been undertaken to explore possible pathways for these transformations including transfer of the PPh2- anion from [B(PPh2 )2 pin]- to the 4-position of a borenium/boronium activated pyridine and concerted pathways for 1,2-addition via intramolecular nucleophilic attack of PPh2 at C2 of a Ph2 PBpin-coordinated pyridine via a four-centered transition state and intramolecular transfer of PPh2 to the 2-position of a boron-activated pyridine in a phosphido-bridged dimer involving a six-centered transition state.

The effect of end-capping groups in A-D-A type non-fullerene acceptors on device performance of organic solar cells

A series of novel wide bandgap small molecules (IFT-ECA, IFT-M, IFT-TH and IFT-IC) based on the A-D-A structure with indenofluorene core, thiophene bridge, and different electron-deficient end-capping groups, were synthesized and used as non-fullerene acceptors in organic solar cells. The influences of end-capping groups on the device performance were studied. The four materials exhibited different physical and chemical properties due to the variation of end-capping groups, which further affect the exciton dissociation, charge transport, morphology of the bulk-heterojunction films and device performance. Among them, IFT-IC-based device delivered the best power conversion efficiency of 7.16% due to proper nano-scale phase separation morphology and high electron mobility, while the devices based on the other acceptors achieved lower device performance (4.14% for IFT-TH, <1% for IFT-ECA and IFT-M). Our results indicate the importance of choosing suitable electron-withdrawing groups to construct high-performance non-fullerene acceptors based on A-D-A motif.

Copper-Catalyzed Regioselective Monodefluoroborylation of Polyfluoroalkenes en Route to Diverse Fluoroalkenes.

Monodefluoroborylation of polyfluoroalkenes has been achieved in a regioselective manner under mild conditions via copper catalysis. The method has shown an extremely broad scope of substrates, including (difluorovinyl)arenes, tetrafluoroethylene (TFE), (trifluorovinyl)arenes, and trifluoromethylated monofluoroalkenes. The choice of boron source was important for the efficient transformation of (difluorovinyl)arenes; (Bpin)2 was suitable for substrates with an electron-deficient aryl group and (Bnep)2 for those with an electron-rich aryl group. Derivatization of the (fluoroalkenyl)boronic acid esters to the corresponding potassium trifluoroborate salts has rendered the products easily isolable, which greatly improved the synthetic practicality of the monodefluoroborylation reaction. Stoichiometric experiments indicate that the fate of the regioselectivity depends on the mode of β-fluorine elimination, which depends on the substrate. Further transformation of the boryl group has allowed facile preparation of fluoroalkene derivatives as exemplified by the synthesis of a fluoroalkene mimic of atorvastatin, which potently inhibited the enzyme activity of HMG-CoA reductase.

From Mechanistic Study to Chiral Catalyst Optimization: Theoretical Insight into Binaphthophosphepine-catalyzed Asymmetric Intramolecular [3 + 2] Cycloaddition

Density functional M11 was used to study the mechanism and enantioselectivity of a binaphthophosphepine-catalyzed intramolecular [3 + 2] cycloaddition reaction. The computational results revealed that this reaction proceeds through nucleophilic addition of the phosphine catalyst to the allene, which yields a zwitterionic phosphonium intermediate. The subsequent stepwise [3 + 2] annulation process, which starts with the intramolecular nucleophilic addition of the allenoate moiety to the electron-deficient olefin group, determines the enantioselectivity of the reaction. This step is followed by a ring-closing reaction and water-assisted proton-transfer process to afford the final product with concomitant regeneration of the phosphine catalyst. Theoretical predictions of the enantioselectivity for various phosphine catalysts were consistent with experimental observations, and 2D contour maps played an important role in explaining the origin of the enantioselectivity. Moreover, on the basis of our theoretical study, new binaphthophosphepine catalysts were designed and that are expecting to afford higher enantioselectivity in this cycloaddition reaction.

A highly specific BODIPY-based fluorescent probe for the detection of nerve-agent simulants

Nerve agents such as Sarin, Soman and Tabun are all very toxic organophosphorus (OP) compounds capable of being used as chemical weapons. Unfortunately, the ability to rapidly sense OPCs is still an ongoing challenging. In this report, we designed and synthesized a fast-response fluorescent probe (1) for the detection of OP nerve agent simulants with high selectivity and sensitivity. The probe contains an electron donor-to-acceptor system in which a BODIPY moiety acts as a reporter group and the hydroxyl group as a reaction site for nerve agent simulants. The electron deficient nitrile group was introduced to lower the background fluorescence of the probe. A significant enhancement of fluorescence intensities at 531nm was observed upon gradual addition of nerve agent simulants on excitation at 480nm. The emission intensity rapidly reached its maximum within only 540s on adding 6 equiv. of nerve agent simulants with a quantum yield of the reaction product of 0.808, 81-fold larger than the probe itself (Ф=0.01). A color change in following a paper test experiment verified its portable application.

Mycobacterial F420H2-Dependent Reductases Promiscuously Reduce Diverse Compounds through a Common Mechanism.

An unusual aspect of actinobacterial metabolism is the use of the redox cofactor F420. Studies have shown that actinobacterial F420H2-dependent reductases promiscuously hydrogenate diverse organic compounds in biodegradative and biosynthetic processes. These enzymes therefore represent promising candidates for next-generation industrial biocatalysts. In this work, we undertook the first broad survey of these enzymes as potential industrial biocatalysts by exploring the extent, as well as mechanistic and structural bases, of their substrate promiscuity. We expressed and purified 11 enzymes from seven subgroups of the flavin/deazaflavin oxidoreductase (FDOR) superfamily (A1, A2, A3, B1, B2, B3, B4) from the model soil actinobacterium Mycobacterium smegmatis. These enzymes reduced compounds from six chemical classes, including fundamental monocycles such as a cyclohexenone, a dihydropyran, and pyrones, as well as more complex quinone, coumarin, and arylmethane compounds. Substrate range and reduction rates varied between the enzymes, with the A1, A3, and B1 groups exhibiting greatest promiscuity. Molecular docking studies suggested that structurally diverse compounds are accommodated in the large substrate-binding pocket of the most promiscuous FDOR through hydrophobic interactions with conserved aromatic residues and the isoalloxazine headgroup of F420H2. Liquid chromatography-mass spectrometry (LC/MS) and gas chromatography-mass spectrometry (GC/MS) analysis of derivatized reaction products showed reduction occurred through a common mechanism involving hydride transfer from F420H- to the electron-deficient alkene groups of substrates. Reduction occurs when the hydride donor (C5 of F420H-) is proximal to the acceptor (electrophilic alkene of the substrate). These findings suggest that engineered actinobacterial F420H2-dependent reductases are promising novel biocatalysts for the facile transformation of a wide range of α,β-unsaturated compounds.

Fluorescence regulation of 4-aminobenzofluoran and its applications for Cu2+-selective fluorescent probe and bioimaging

Fluoran dyes, a large family of colourants, have been widely used as thermosensitive dyes in print industry by taking advantage of the thermo-controlled interconversions between the colorless spirolactone and the colored zwitterion forms. But few attentions have been paid to their fluorescence properties. In this paper, the fluorescence regulation of 4-aminobenzofluoran dye 1 by introducing of electron-deficient acetyl group to tune the energy level of the highest occupied molecular orbital (HOMO) of the amino group has been carried out. Based on this strategy, the N-acetylated product BF derived from its precursor 1 shows stable UV–Vis and fluorescence spectra in water from pH 1.0 to 12.0 due to the blocking of the photoinduced electron transfer (PET) process from the amino group to the excited state of fluoran chromophore. Moreover, BF is cell permeable and can be used as signal reporter for the design of fluorescence probes by taking advantage of the fluorescence controlled mechanism of the ring opening and closing chemical processes of the spirolactone platform. By using BF as precursor, a highly sensitive and selective fluorescent probe BF-Cu for Cu2+ was synthesized by introducing a Cu2+-responsive water soluble 2-hydroxylethyl hydrazine functional group. We expect that the fluorescence recovery of fluoran dyes via the regulation of the HOMO energy level of the amino group enable an additional synthetic effort on the development of fluorescence fluoran dyes and expansion of their applications.

Fine-tuning the emissions of highly efficient thermally activated delayed fluorescence emitters with different linking positions of electron-deficient substituent groups

To further develop a simple method for emission fine-tuning, two novel thermally activated delayed fluorescence (TADF) emitters, 5′-(10H-phenoxazin-10-yl)-[1,1′:3′,1″-terphenyl]- 2′,4,4″- tricarbonitrile (mPTBC) and 2′-(10H-phenoxazin-10-yl)-[1,1′:3′,1″- terphenyl]-4,4″,5′-tricarbonitrile (oPTBC) have been designed and synthesized by employing exactly the same functional units, a ter-benzonitrile and a phenoxazine (PXZ). By adjusting the linking position of the two electron-deficient benzonitrile arms from a meta-position to an ortho-position with the cyano core, the LUMO energy levels of mPTBC and oPTBC are varied to −2.98 and −3.13 eV, respectively; while the HOMO energy levels remain similar. In devices, the new TADF emitters successfully exhibit similar maximum efficiencies, but different-color emissions with a spectral peak at 516 nm for mPTBC and a spectral peak at 540 nm for oPTBC. These results prove the simple modification of adjusting the linking position of electron-deficient substituent groups in the molecules can effectively fine-tune the emissions of TADF emitters but without significantly changing other key performance.

New Fluorescent Conjugates Displaying Solvatochromic Properties

AbstractFour new fluorescent dyes based on bis(phenyl‐ethynyl‐)‐2‐naphthyl (BPEN) were designed and synthesized. To improve the solvatochromic property and enhance the brightness of the fluorescent BPEN, an electron‐donating unit of azetidine and/or an electron deficient group of ‐NO2 was introduced. The corresponding fluorophores are denoted as T1, T2, T3 and T4, respectively. Moreover, to facilitate derivatization of the probes, two ethoxy carbonyl residues were grafted onto the side positions of BPEN. Spectroscopic studies demonstrated that introduction of azetidine leads to superior solvatochromic properties and largely enhanced fluorescence quantum yields as evidenced by the fact that T3 shows more than 150 nm shift in its maximum emission when dissolved in solvents of very different polarities and displays high fluorescence quantum yields in the solvents studied. However, T2, which is the one bearing a ‐NO2 group, is non‐fluorescent. Theoretical analysis and Lippert‐Mataga modeling revealed the intra‐molecular charge transfer (ICT) nature of the solvatochromic behavior of the compounds. Further test reveals that the fluorophores, in particular T3, are sensitive to the presence of trace water in less polar solvents, such as THF and 1,4‐dioxane. Moreover, it is believed that the new fluorophores may serve as building blocks for creating environment‐sensitive fluorescent sensors.

Fine-tuning π-spacer for high efficiency performance DSSC: A theoretical exploration with [formula omitted] based organic dye

Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches, a series of triphenylamine based organic dyes that modified by electron-withdrawing (EW) or electron-deficient (ED) substituent groups are investigated. The properties of all the isolated dyes, including frontier molecular orbital, intramolecular charge transfer, absorption spectra, maximal photon generated current (Jph) and intermolecular interaction between dye and I2 are investigated theoretically to confirm which dyes can produce great performance for dye-sensitized solar cell (DSSC). Subsequently, the structures of dye combined with (TiO2)64 cluster are optimized by means of Vienna ab initio simulation package (VASP) code. Then the interfacial interaction between the dye and semiconductor is further discussed to reveal the interfacial charge injection process by means of interfacial electron transfer code. The importance of fine-tuning π-spacer is also demonstrated by the density of state (DOS) plot and photo-induced charge transfer dynamics. Compared with other dyes, TA-CN dye shows outstanding performance because of the strong coupling of the absorbed dye's orbitals with substrate orbitals and the fast as well as complete charge injection process. The purpose of our study is expected to provide a promising way to design possible candidate sensitizers for DSSC.

Efficient Deep-Blue Electroluminescence Based on Phenanthroimidazole-Dibenzothiophene Derivatives with Different Oxidation States of the Sulfur Atom.

Developing efficient deep-blue materials is a long-term research focus in the field of organic light-emitting diodes (OLEDs). In this paper, we report two deep-blue molecules, PITO and PISF, which share similar chemical structures but exhibit different photophysical and device properties. These two molecules consist of phenanthroimidazole and dibenzothiophene analogs. The distinction of their chemical structures lies in the different oxidation states of the S atom. For PITO, the S atom is oxidized and the resulting structure dibenzothiophene S,S-dioxide becomes electron deficient. Therefore, PITO displays remarkable solvatochromism, implying a charge-transfer (CT) excited state formed between the donor (D) phenanthroimidazole and acceptor (A) dibenzothiophene S,S-dioxide. For PISF, it is constituted of phenanthroimidazole and dibenzothiophene in which the S atom is not oxidized. PISF displays locally excited (LE) emission with little solvatochromism. Compared with PISF, the D-A molecule PITO with an electron-deficient group shows a much lower LUMO energy level, which is in favor of electron injection in device. In addition, PITO exhibits more balanced carrier transport. However, PISF is capable of emitting in the shorter wavelength region, which is beneficial to obtain better color purity. The doped electroluminescence (EL) device of the D-A molecule PITO manifests deep-blue emission with CIE coordinates of (0.15, 0.08) and maximum external quantum efficiency (EQE) of 4.67 %. The doped EL device of the LE molecule PISF, however, reveals an even bluer emission with CIE coordinates of (0.15, 0.06) and a maximum EQE of 4.08 %.

Development of the HERON Reaction: A Historical Account

This account describes the discovery and development of the HERON reaction, a reaction with special connection to the Heron Island Conferences on Reactive Intermediates and Unusual Molecules. This modern ‘named’ reaction describes an unusual rearrangement of bisheteroatom-substituted amides RCON(X)(Y) whereby the more electron deficient group, X, migrates from nitrogen to the carbonyl carbon giving an acyl derivative, RC(O)X, and Y-stabilised nitrenes. In it, the origins, mechanistic elucidation, and theoretical validation are described in more or less chronological order. Along that time line we introduce the concepts of ‘anomeric amides’, ‘amidicity’ in anomeric amides, and their role in the HERON reaction. All known versions of the reaction that have since been discovered are outlined and a basic understanding of the relative roles of reduced resonance and the anomeric driving force, both functions of the heteroatom substituents at the amide nitrogen, are quantified.

Exploring the electrochromic properties of poly(thieno[3,2-b]thiophene)s decorated with electron-deficient side groups

Electron-deficient cyanophenyl side groups decrease the response time and drastically improve the stability of electrochromic polymers.