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A novel solid Bronsted-Lewis acid catalyst La-PW-SiO2/SWCNTs was synthesized from the synergistic modification of H3PW12O40 (HPW) by single-walled carbon nanotubes functionalized with sidewall hydroxyl groups (SWCNTs–OH) and La3+ via sol-gel method. The freshly prepared catalyst was characterized by several methods, and the catalytic activity and stability of it were studied from the esterification of oleic acid and methanol. Results showed that the highest conversion of oleic acid was 93.1 wt% and maintained as high as 88.7 wt% after six cycles of La-PW-SiO2/SWCNTs. The high catalytic activity and stability of La-PW-SiO2/SWCNTs can be attributed to the strong electron withdrawing effect of La3+ on π bond of SWCNTs, because it can facilitate the formation of a large number of strong Lewis acid sites. Therefore, the reduction of catalytic activity of a solid acid catalyst due to the fact that hydration reaction of its Bronsted acid sites can be effectively reduced. La-PW-SiO2/SWCNTs can be an efficient and economical catalyst, because it shows good catalytic activity and stability.

Iron porphyrins are synthesized by systematically introducing electron withdrawing groups (EWGs) on pyrroles to evaluate the relationship between rate (k) and overpotential (η). The results indicate that while EWGs lead to a rise in the thermodynamic FeIII/II reduction potential (E0), the potential of O2 reduction reaction (ORR) does not scale with E0. More importantly, the iron porphyrins with higher E0 shows an order of magnitude higher rate of ORR than unsubstituted iron tetraphenyl porphyrin. This contests the scaling relationship often offered to predict rates of ORR by iron porphyrins based on their E0. Mechanistic investigations reveal that the rate determining steps of ORR changes between these iron porphyrins with EWG’s as the pKa and E0 of several key intermediate species have likely changed on altering the macrocycle. These results suggests that linear dependence of log(rate) on E0 or η may only be valid for complexes where the rds of ORR remains the same.

As nitrobenzene (NB) is structurally stable and difficult to degrade due to the presence of an electron withdrawing group (nitro group). The sequential nanoscale zero valent iron-persulfate (NZVI-Na2S2O8) process was proposed in this study for the degradation NB-containing wastewater. The results showed that the NB degradation efficiency and the total organic carbon removal efficiency in the sequential NZVI-Na2S2O8 process were 100% and 49.25%, respectively, at a NB concentration of 200 mg L−1, a NZVI concentration of 0.75 g L−1, a Na2S2O8 concentration of 26.8 mmol L−1, an initial pH of 5, and a reaction time of 30 min, which were higher than those (88.53% and 35.24%, respectively) obtained in the NZVI/Na2S2O8 process. Sulfate radicals ( SO 4 · − ) and hydroxyl radicals ( OH) generated in the reaction were identified directly by electron paramagnetic resonance spectroscopy and indirectly by radical capture experiments, and it was shown that both SO 4 · − and OH played a major role in the sequential NZVI-Na2S2O8 process. The possible pathways involved in the reduction of NB to aniline (AN) and the further oxidative degradation of AN were determined by gas chromatography-mass spectrometry.

Imaging in the shortwave-infrared region (SWIR, λ = 1000-2500 nm) has the potential to enable deep tissue imaging with high resolution. Critical to the development of these methods is the identification of low molecular weight, biologically compatible fluorescent probes that emit beyond 1000 nm. Exchanging the bridging oxygen atom on the xanthene scaffold (C10' position) with electron withdrawing groups has been shown to lead to significant redshifts in absorbance and emission. Guided by quantum chemistry computational modeling studies, we investigated the installation of a ketone bridge at the C10' position. This simple modification extends the absorbance maxima to 860 nm and the emission beyond 1000 nm, albeit with reduced photon output. Overall, these studies demonstrate that broadly applied xanthene dyes can be extended into the SWIR range.

In the course of our research on the structure–activity relationship of 5,6-dihydro-2H-pyran-2-one, (S)-6-[(R)-2-hydroxy-6-(4-fluorophenyl)hexyl]-5,6-dihydro-2H-pyran-2-one was found to show 2-3-fold more potent plant growth inhibitory activity against Italian ryegrass shoots (IC50 = 95 µm) and roots (IC50 = 17 µm) than compound bearing unsubstituted phenyl group. The small and electron withdrawing atom at 4-position of the benzene ring caused the higher activity.

Zinc methyl 3-hydroxymethyl-pyropheophorbides-[Formula: see text] bearing an acetyl or nitro group at the 20-position were prepared by chemically modifying natural chlorophyll-[Formula: see text]. The synthetic zinc 20-substituted bacteriochlorophyll-[Formula: see text] analogs self-aggregated in an aqueous Triton X-100 micelle solution to give red-shifted and broadened electronic absorption bands, similarly as in one of the photosynthetic light-harvesting antennas, chlorosomes. Although the sterically bulky 20-substituents of the semisynthetic zinc 31-hydroxy-131-oxo-chlorins partially disturbed the chlorosomal self-aggregates which would be produced by the [Formula: see text]–[Formula: see text] stacking of the chlorin chromophores, their electron-withdrawing abilities should enhance the specific, intermolecular interaction of Zn[Formula: see text]O32–H[Formula: see text]O=C-13 which was essential for the chlorosomal self-aggregation. Such self-assemblies using these model pigments would provide a new clue for constructing of artificial photosynthetic systems.

The dumbbell-shaped type-I conformation is the inherent structure of the [26]hexaphyrin(1.1.1.1.1.1) framework without any perturbations from its peripheral substituents. Conversely, the rectangular type-II conformation can be regarded as a more general structure seen in stable [26]hexaphyrins(1.1.1.1.1.1) because of not only the synthetic limitations but also the steric influences related to the meso-aryl substituents. In this study, the synthesis of [26]hexaphyrins(1.1.1.1.1.1) bearing a series of electron-withdrawing groups and their conformational characterizations were investigated. The 1H NMR spectra showed that [26]hexaphyrin with 3,5-dinitrophenyl groups at the 5,20-positions was obtained as the sole type-I conformer, whereas most other [26]hexaphyrins are in equilibrium between type-I, type-II, and type-II[Formula: see text] conformers. Moreover, UV-vis absorption measurements revealed that type-I conformations can utilize the electronic features of their 5,20-substituents owing to their relatively co-planar arrangements with the macrocycles.

The central role of Coulombic interactions in enzyme catalysis has inspired multiple approaches to sculpting electrostatic potential fields (EPFs) for controlling chemical reactivity, including ion gradients in water microdroplets, the tips of STMs, and precisely engineered crystals. These are powerful tools because EPFs can affect all reactions, even those whose mechanisms do not involve formal charges. For some time now, supramolecular chemists have become increasingly proficient in using encapsulation to control stoichiometric and catalytic reactions. However, the field has not taken advantage of the broad range of nanocontainers available to systematically explore how EPFs can affect reactions within their inner-spaces. With that idea in mind, previously, we reported on how positively and negatively charged supramolecular capsules can modulate the acidity and reactivity of thiol guests bound within their inner, yoctoliter spaces (Cai, X.; Kataria, R.; Gibb, B. C. J. Am. Chem. Soc. 2020, 142, 8291–8298; Wang, K.; Cai, X.; Yao, W.; Tang, D.; Kataria, R.; Ashbaugh, H. S.; Byers, L. D.; Gibb, B. C. J. Am. Chem. Soc.2019, 141, 6740–6747). Building on this, we report here on the cyclization of 14-bromotetradecan-1-amine inside these yoctoliter containers. We examine the rate and activation thermodynamics of cyclization (Eyring analysis), both in the absence and presence of exogenous salts whose complementary ion can bind to the outside of the capsule and hence attenuate its EPF. We find the cyclization rates and activation thermodynamics in the two capsules to be similar, but that for either capsule attenuation of the EPF slows the reaction down considerably. We conclude the capsules behave in a manner akin to covalently attached electron donating/withdrawing groups in a substrate, with each capsule enforcing their own deviations from the idealized SN2 mechanism by moving electron density and charge in the activated complex and TS, and that the idealized SN2 mechanism inside the theoretical neutral host is relatively difficult because of the lack of solvation of the TS.

4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene (BODIPY) and derivatives are an outstanding class of fluorescent dyes. Herein, we report on the introduction of a nitrosyl moiety into the BODIPY structure and its dramatic effect on the observed electrochemical reaction mechanism. 6-Nitrosyl-8-phenyl-BODIPY and its 5-nitrosyl positional isomer, compounds 2 and 3, respectively, were obtained from the meso precursor, 8-phenyl-BODIPY (1), by nitrosation. Electrochemical studies for 1–3 are reported. Cyclic voltammetry and differential pulse voltammetry in degassed DMF or in MeCN (reduction+oxidation), both with n-Bu4NPF6 (0.1 mol L−1), were obtained. Compound 1 displays the usual behaviour for 8-phenyl substituted BODIPYs. The addition of the acceptor nitroso group in compounds 2 (in position β) and 3 (in position α), leads to a different profile. For all the compounds, the nitroso group greatly facilitates the reductions. For compound 3 (EpIc=−0.238 V), the first to be reduced is the nitroso group, due to the stability of the electrogenerated radical anion, along with non-bonding interactions with the electronegative boron difluoride. This is different from compound 2 (EpIc=−0.351 V) with a β-nitroso group, where the nitroso-based facilitated reduction occurs in the substituted BODIPY core. Spectroelectrochemistry coupled with analysis through conceptual density functional theory (CDFT) corroborate the voltammetric results and explain the unexpected reactivity differences.

The combination of strong electron-withdrawing groups in cyclometalated N-heterocyclic carbene ligands (C^C*) with known beneficial auxiliary ligands in phosphorescent platinum(II) complexes leads to efficient light-to-deep-blue emission with quantum yields of up to 92%. All compounds were characterized and investigated regarding their photophysical, electrochemical, and thermal properties, and three complexes could additionally be characterized by solid-state structures. Density functional theory calculations (PBE0/6-311G* with dispersion correction) are reported.

The coumarin skeleton has been a focus of attention for many years, and its fluorescence properties vary depending on the substituents. Fluorescent coumarin derivatives are useful tools for many strategies have been developed for their synthesis. Although 7-diethylaminocoumarin has excellent fluorescence properties, it is unstable. We have developed a facile strategy for the synthesis of 7-diethylaminocoumarin derivatives by increasing the electrophilicity of the ynone moiety to promote nucleophilic addition reactions and cyclization. The reaction tolerates a variety of substitutions at the 4-position.

A nitro group is a common fluorescence quencher, but its quenching efficiency can be easily affected by the surrounding environment. To date, there has been no systematic study on the effects of electron-withdrawing groups on the quenching efficiency of nitro groups. Herein, by virtue of experimental validation and theoretical calculations, we found that strong electron-withdrawing groups, such as pyridinium and dicyanovinyl groups, are detrimental to the quenching effect of nitro groups. Decreasing the electron-withdrawing ability could restore the nitro group’s quenching effect.

Purpose: A series of benzylidene-2-(4-bromophenoxy)-2-methyl propane hydrazides (1-10) were synthesized and assay them for their biofilm inhibition, antioxidant and mutagenic. Methods: All derivatives were prepared by condensation of various substituted benzaldehyde and acetophenones with 2-(4-bromorophenoxy)-2-methyl propane hydrazide, which was itself prepared by hydrazinolysis of ethyl-2-(4-bromophenoxy)-2-methyl propanoate and were characterized by FTIR, 1H NMR 13C NMR, mass spectrometry. They were screened for their in-vitro anti-oxidant, biofilm inhibition and mutagenicity by established methods. Results: Anti-oxidant results revealed that the electron donating group enhanced the scavenging ability of the compounds as seen in compounds 4b, 4h and 4i. In biofilm inhibition studies, all compounds were more active against Gram –ive bacterial strain when compared to gram +ive strain. The mutagenicity assay results indicate that the compound having chloro group substitution is mutagenic. Conclusion: The benzylidine compounds of 2-(4-bromophenoxy)-2-methyl hydrazide possessing electron donating substituents exhibit superior activities to the electron withdrawing group substituents.

This study presents the benchmark calculations of proton affinities (PAs) and gas-phase basicities (GBs) of 8-para substituted benzaldehyde compounds using the multilevel model chemistries (G3B3 and G4), density-functional quantum model (B3LYP) and ab initio model (MP2). The results show that the computed properties are strongly correlated with the available experimental data. The PAs and the GBs of other eight para-substituted benzaldehyde compounds, for which the experimental data does not currently exist, have been calculated using G3B3 and B3LYP methods. The correlations between the experimental PAs and GBs with the computed properties such as PA, GB, chemical properties (bond lengths, electron density and δ1 H NMR chemical shift) of the investigated benzaldehydes have been studied and statistically analyzed. The influence of the substituted groups has been discussed in terms of inductive effect and electron donating and electron withdrawing effect. The results obtained show that the chemical properties of the benzaldehyde compounds are controlled by the strong coupling between the CHO group and the nature of the para-substituent groups through the benzene ring as a conducting linkage.

A hitherto unreported heterocyclic imide, thiadiazolo[3,4-g]quinoxaline-fused acenaphthenequinone imide acceptor (TQAI), is designed and synthesized by incorporating an auxiliary electron-deficient...

Perfluoro phthalonitrile substituted separately with perfluoroalkyl (EWG) and NH2, NHMe, and NMe2 (EDG) groups generate a series of aromatic C-H bonds-free nitriles that can now lose electrons, whose HOMO–LUMO gap is narrowed by EDG beyond the level induced by EWG, and whose dipole moments double. Molecular parameters vary linearly with Hammett’s free-energy constants, their electronic underpinning being uncovered by DFT calculations. The phthalonitriles’ assembling in solid-state structures is determined by forces that transition from van der Waals, in the case of EWG, to H-bonding and/or [Formula: see text]-stacking interactions in the case of EDG, as revealed by their single-crystal X-ray structures.

Alkyne metathesis represents a rapidly emerging synthetic method that has shown great potential in small molecule and polymer synthesis. However, its practical use has been impeded by the limited availability of user-friendly catalysts and their generally high moisture/air sensitivity. Herein, we report an alkyne metathesis catalyst system that can operate under open-air conditions with a broad substrate scope and excellent yields. These catalysts are composed of simple multidentate tris(2-hydroxyphenyl)methane ligands, which can be easily prepared in multi-gram scale. The catalyst substituted with electron withdrawing cyano groups exhibits the highest activity at room temperature with excellent functional group tolerance (-OH, -CHO, -NO2, pyridyl). More importantly, the catalyst provides excellent yields (typically >90%) in open air, comparable to those operating under argon. When dispersed in paraffin wax, the active catalyst can be stored on a benchtop under ambient conditions without any decrease in activity for one day (retain 88% after 3 days). This work opens many possibilities for developing highly active user-friendly alkyne metathesis catalysts that can function in open air., Alkyne metathesis catalysts usually suffer from high moisture/air sensitivity, which limit their wide applicability. Here, the authors report efficient alkyne metathesis catalysts that can operate under open-air conditions with a broad functional group tolerance.

Fifteen chalcone derivatives having D–A–D, D–A–A and A–A–D architectures have been synthesized by Claisen–Schmidt condensation reaction and characterized by UV–Vis, IR, 1H-NMR, 13C-NMR and Mass spectrometry. In order to unambiguously establish the structure–activity relationship for the non-linear optical activity of these compounds, for the first time to our knowledge, we use the femtosecond degenerate four wave mixing (DFWM) technique to quantify and compare the third-order non-linear optical (NLO) activity of all the 15 compounds, under identical conditions. The second harmonics generation (SHG) efficiencies for all the compounds have also been evaluated using the Kurtz-Perry powder method. Among the compounds that we have synthesized here, the ones with A–A–D architecture show the highest NLO activity. Our results show that the NLO activity of a compound with A–A–D architecture can be further enhanced by incorporating a substituent with strong electron withdrawing ability on ring A and strong electron donating substituent on ring B. The results of the in silico studies that we have carried out correlate well with our experimental findings. The compounds (E)-3-(4-(dimethylamino)phenyl)-1-(4-nitrophenyl)prop-2-en-1-one with the compound code (4-N(CH3)2–4′-NO2) and (E)-3-(4-methoxyphenyl)-1-(4-nitrophenyl)prop-2-en-1-one with the compound code (4-MeO-4′-NO2) show the highest NLO activity among the compounds we have reported here.

The reactivity of NiII and PdII olefin polymerization catalysts can be enhanced by introduction of electron-withdrawing substituents on the supporting ligands rendering the metal centers more electrophilic. Reported here is a comparison of ethylene polymerization activity of a classical salicyliminato nickel catalyst substituted with the powerful electron-withdrawing 2,4,6-triphenylpyridinium (trippy) group to the -CF3 analogue. The trippy substituent is substantially more electron-withdrawing (σmeta =0.63) than the trifluoromethyl group (σmeta =0.43) which results in a ca. 8-fold increase in catalytic turnover frequency. An additional advantage of trippy is the high steric bulk relative to the trifluoromethyl group. This feature results in a four-fold increase in polymer molecular weight owing to enhanced retardation of chain transfer. A significant increase in catalyst lifetime is observed as well.

We report on the molecular structure of trimethylsilanes Si(CH3)(3)X in which the substituents X, namely (Z)-pentafluoropropen-1-yl, trifluoropropyn-1-yl, pentafluoroethyl, trifluorovinyl, vinyl, propyn-1-yl, di- and trichloromethyl, display electron withdrawing effects of varying strength. The lengths of the bonds between the silicon and the carbon atoms of X correlate with the hybridization of the respective orbitals and the steric demand of X rather than with the electron withdrawing capability. In case of chlorinated substituents dispersion effects seem to shorten the Si-C bond. Furthermore, a route for generating trifluoropropyn-1-yllithium from the cryogen 2,3,3,3-tetrafluoropropene (HFO-1234yf) and n-butyllithium is described. Tetrafluoropropen-1-yllithium is slowly formed at -80 degrees C but even at this temperature spontaneous elimination of LiF occurs. Deprotonation of the formed 3,3,3-trifluoropropyne requires temperatures of above -60 degrees C leading to trifluoropropyn-1-yllithium which appears as relatively stable at room temperature.

Electrochemical reduction of different aryldiazonium salts in aqueous solution was studied in this work and it is shown that the aryldiazonium salts are converted to the corresponding aryl radical and aryl anion. The results of this research indicate that the reduction of aryldiazonium salts takes place in two single-electron steps. Our data show that when the substituted group on the phenyl ring is H, Cl, OH, NO2, OCH3 or SO3−, the corresponding diazonium salt shows poor adsorption characteristics, but when the substituted group is methyl, the corresponding diazonium salt shows strong adsorption characteristics. In the latter case, the voltammogram exhibits three cathodic peaks. In addition, the effect of various substitutions on the aryldiazonium reduction was studied by Hammett's method. The data are show that with increasing electron withdrawing capacity of the substituent, the reduction of corresponding diazonium salt becomes easier.

The synthesis of two novel n-type molecular organic semiconductors based on a fluorinated indacenodithiophene core in combination with an electron withdrawing N-cyanoimine group is reported, and the influence of the regiochemistry of the solubilizing sidechain is investigated. The N-cyanoimine is confirmed to be a strongly electron accepting group, which in combination with the core fluorination resulted in high electron affinities for both materials. Single crystal analysis demonstrated that whilst both materials arrange in ordered slipped stacks with close π–π stacking distances (∼3.40 Å), significant differences in electron transfer integrals for the two regioisomers were observed, relating to differences in relative molecular displacement along the π-stacking direction. Organic thin-film transistors fabricated via blade-coating displayed electron mobility up to 0.13 cm2 V−1 s−1 for the isomer with the larger transfer integral.

A high-yielding total synthesis of daptomycin, an important clinical antibiotic, is described. Key to the development of this synthesis was the elucidation of a Camps cyclization reaction that occurs in the solid-phase when conventionally used kynurenine (Kyn) synthons, such as Fmoc-l-Kyn(Boc,CHO)-OH and Fmoc-l-Kyn(CHO,CHO)-OH, are exposed to 20% 2-methylpiperidine (2MP)/DMF. During the synthesis of daptomycin, this side reaction was accompanied by intractable peptide decomposition, which resulted in a low yield of Dap and a 4-quinolone containing peptide. The Camps cyclization was found to occur in solution when Boc-l-Kyn(Boc,CHO)-Ot-Bu and Boc-l-Kyn(CHO,CHO)-OMe were exposed to 20% 2MP/DMF giving the corresponding 4-quinolone amino acid. In contrast, Boc-l-Kyn(CHO)-OMe was stable under these conditions, demonstrating that removing one of the electron withdrawing groups from the aforementioned building blocks prevents enolization in 2MP/DMF. Hence, a new synthesis of daptomycin was developed using Fmoc-l-Kyn(Boc)-OH, which is prepared in two steps from Fmoc-l-Trp(Boc)-OH, that proceeded with an unprecedented 22% overall yield. The simplicity and efficiency of this synthesis will facilitate the preparation of analogs of daptomycin. In addition, the elucidation of this side reaction will simplify preparation of other Kyn-containing natural products via Fmoc SPPS.

Reaction of Na[VO(tBuO)4] (generated in situ from VOCl3 and NaOtBu) with p-tert-butyltetrahomodioxacalix[6]areneH6 (L1H6) afforded, after work-up (in MeCN), the mixed-metal complex [(VO)2(μ-O)Na2(L1)(MeCN)4]·5(MeCN) (1·5MeCN), whilst the oxo complex {[VO]4L1} (2·6MeCN) was isolated via the use of [VO(OnPr)3]. Reaction of L1H6 with [V(Np-CH3C6H4)(OtBu)3] afforded the complex {[V(Np-CH3C6H4)]2L1} (3·7MeCN·0.5CH2Cl2). Use of similar methodology afforded the imido complexes {[V(Np-RC6H4)]2L1} (R = OMe (4); CF3 (5); Cl (6); F (7)); on one occasion, reaction of [V(Np-CH3C6H4)(OEt)3] with L1H6 afforded the product [VO(L2)]2·4MeCN (8·4MeCN) (L2 = 2-(p-CH3-C6H4NCH)-4-tBu-C6H2O-6-CH2)-4-tBuC6H2OH) in which L1 has been cleaved. For comparative catalytic ring opening polymerization (ROP) studies, the known complexes [VOL3] (L3 = oxacalix[3]arene) (I), [V(Np-CH3-C6H4)L3]2 (II), [Li(MeCN)4][V2(O)2Li(MeCN)(L6H2)2] (L6H6 = p-tert-butylcalix[6]areneH6) (III) and [(VO)2L8H] (L8H8 = p-tert-butylcalix[8]areneH8) (IV) have also been prepared. ROP studies, with or without external alcohol present, indicated that complexes 1 to 8 exhibited moderate to good conversions for e-Cl, δ-VL and the co-polymerization thereof. Within the imido series, a positive influence was observed when electron withdrawing substituents were present. These systems afforded relatively low molecular weight products and were also inactive toward the ROP of rac-lactide. In the case of ethylene polymerization, complexes 3, 5 and 7 exhibited highest activity when screened in the presence of dimethylaluminium chloride/ethyltrichloroacetate; the activity of 4 was much lower. The products were highly linear polyethylene with Mw in the range 74–120 × 103 Da.

An efficient and versatile method for the synthesis of 1,4-diaryl tetrazolones 1 is reported which involves C–N coupling of aryl tetrazolones 2 with aryl boronic acids 3 in the presence of Cu2O nanoparticles under an oxygen atmosphere and DMSO as solvent. The reaction tolerates a variety of electron donating and electron withdrawing substituents on both substrates and produces the desired 1,4-diaryl tetrazolones 1 in moderate to good yields. In the crystal lattice, the molecules exhibit π⋯π stacking interactions between the adjacent layers as well as weak through-space electrostatic C–H⋯O interactions involving the pendant rings and tetrazolone carbonyl. 1-(4-Methoxyphenyl)-4-(3-tolyl)-1,4-dihydro-5H-tetrazol-5-one 1bk and 1-(3-fluorophenyl)-4-(4-methoxyphenyl)-1,4-dihydro-5H-tetrazol-5-one 1be, differing only in the presence of one group (methyl or fluoro), exhibited an identical pattern of noncovalent interactions in the solid-state. Hirshfeld surface analyses have also been performed to visualize intermolecular interactions.

To explore the role of substituents on ligands in the modification of metal catalysts, a series of Ru–amide/AC catalysts are synthesized with various amide ligands derived from formamide and assessed for acetylene hydrochlorination. Activity evaluation reveals a rule that replacing a hydrogen on formamide with an electron donor substituent can enhance the catalytic performance, while electron withdrawing substituents have the opposite effect. However, formanilide, which violates this law, shows the best modification effect, which is proved to be the effect of steric hindrance by characterization and DFT calculation. Therefore, another rule is concluded that the electron donor ability and steric hindrance of substituents on amide ligands jointly affect the modification effect. Finally, benzanilide, with a superior modification effect, which searched based on the above results, gives strong evidence for the correction of these rules. This work provides a theoretical basis for the search for efficient ligands for acetylene hydrochlorination.

The selective late-stage functionalization of BN-containing polycyclic aromatic hydrocarbons (BN-PAHs) is very challenging. Herein, dithienoazaborines (BNDT, 3a and 3b) were synthesized as model compounds, and two kinds of selective functionalized BNDT precursors, 4a and 4b were synthesized due to the strong polar effect of the BN bond, leading to a series of BNDT derivatives for the following coupling reactions. Based on this, two kinds of BNDT-based small molecules and oligomers with BN bonds on the conjugated main chain and side chain were synthesized accordingly. The BNDT derivatives (5b/6b/7b) with a BN bond on the conjugated side chain showed lower LUMO energy levels and narrower band gaps than those with a BN bond on the conjugated main chain (5a/6a/7a). Different modifications and polymerization have effects on the photophysical properties and all derivatives are highly selective to fluoride ions. This work realized a new strategy for selective late-stage functionalization of BN-PAHs with selective π-conjugated extension, laying a solid foundation for the subsequent BN chemistry and application of functionalized BN-PAHs.

A series of dyes with the D-π-A architecture has been designed and studied for dye sensitized solar cells (DSSCs). We have used phenothiazine (PTZ) and coumarin (COU) derivatives as the donor unit and benzopyrrole (BTZ) and 2-methyl-2H-isoindole-1,3-(3aH,7aH)-diene (IND) as the acceptor unit along with the azomethine group and thiophene ring as the π-spacer unit. Three electron donating groups viz. -CH3, -NH2, and -OH and four electron withdrawing groups viz. -CF3, -COCl, -F and -NO2 have been attached at the donor and the acceptor units respectively of the four unsubstituted dyes COU-BTZ, PTZ-BTZ, COU-IND and PTZ-IND. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods have been employed to investigate the structural, electronic and photochemical properties of these dyes. The study reveals that the unsubstituted dye PTZ-BTZ possesses the lowest value of ΔH-L. Our study also reveals that attachment of the -NO2 group at the acceptor unit lowers the ΔH-L values of all the dye molecules. We have observed that the excited state oxidation potential (ESOP) of all the dyes lies above the conduction band of the TiO2 semiconducting surface. However, the ground state oxidation potential (GSOP) of most of the dyes belonging to the COU-BTZ and COU-IND groups lies below the redox potential of the I-/I3- redox couple. The total reorganization energy (λtot) values of the COU-BTZ and COU-IND groups of dyes are observed to be low compared to the other groups of dyes. The study of the charge transport properties of the dyes confirms that the designed dyes will act as electron transport materials. The absorption properties of the dyes show that the COU-BTZ group of dyes possesses the maximum values of the absorption wavelength (λmax values) and attaching the -NO2 group at the acceptor unit shifts the λmax values of all the dyes to the longer region. From the study of the electronic properties of the dye-TiO2 complexes it has been observed that the performance of the dyes has been enhanced compared to the isolated dye molecules.

Synthetic oligosaccharides are objects of interest as model compounds in studies on the biological activity of natural compounds, but also as components for new drugs, glycoconjugate vaccines, carbohydrate diagnostic agents and various other products. The key stage in oligosaccharide synthesis is the glycosylation reaction, which leads to the formation of a linkage between carbohydrate fragments. This review highlights a current problem in modern glycochemistry – the methods of stereocontrol in the glycosylation reaction. Protecting groups within the structure of glycosyl donors are considered as stereocontrolling factors, affecting the reaction mechanism by means of (1) participation or anchimeric assistance, (2) deactivation, (3) intramolecular aglycone delivery. The well-established mechanism of neighboring group participation at O-2 for the synthesis of 1,2- trans glycosides is shown, as well as its modern modifications, including activating ethers, chiral protecting groups and achiral bicyclic glycosyl donors. The mechanisms of remote participation from O-3, O-4 and O-6 of the glycosyl donor are discussed in detail. In addition, approaches to stereocontrol using deactivating protection (conformation constraining and electron withdrawing groups) are described. Finally, synthetic approaches based on intramolecular aglycone delivery are considered. Both classical and novel protecting groups used to control the steric outcome of glycosylation are presented, the mechanisms underlying the presented approaches are discussed in detail, while also showing how the described strategies apply to the synthesis of complex structures.

Electron transport type host materials for blue thermally activated delayed fluorescent (TADF) organic light-emitting diodes (OLEDs) were synthesized by engineering the electron withdrawing CN units in the molecular structure. The two host materials having twisted molecular structure by ortho orientation of dibenzofuran and CN modified carbazole were developed as the electron transport type hosts to obtain high triplet energy for blue TADF application. Two CN units were introduced in the molecular structure for electron transport properties. One host had one CN unit in the phenyl core and one CN unit in the carbazole, and the other host had two CN units in the carbazole. The two hosts showed similar triplet energy above 3.0 eV, but different lowest unoccupied molecular orbital (LUMO) energy levels and orbital distributions. The host with one CN unit in the phenyl core showed superior device performances such as EQE over 20% and device lifetime of 32.2 h up to 80% of initial luminance of 500 cd m−2 as the electron transport type host in the mixed host because of deep LUMO level suppressing electron trapping.

Ionic liquids, which are widely known as room temperature molten salts, have been the subject of much scientific debate for more than a decade. These compounds can be used as green solvents or even as additives in many reactions. Due to their noticeable conductivity, which is a function of the interaction energies existing between the ion pairs in ionic liquids, the synthesis and introduction of new families of these chemicals are of importance. The target of this paper is to design new carboxylate-based ionic liquids containing OH and CF3 groups. Our results indicate that the properties of these ILs are highly affected by the presence of OH and CF3 groups, in which OH stabilizes the negative charge of the anion via intramolecular hydrogen bonds and CF3 stabilizes it through the electron withdrawing effect. These groups decrease the binding energy between the anion and cation of the carboxylate-based ionic liquids and thus affect their physical properties such as melting point and density as well as their chemical properties. All calculations in this study were performed in the gas phase at the B3LYP/6-311++G(d,p) level.

Photosensitizers with high energy, long lasting charge-transfer states are important components in systems designed for solar energy conversion by multistep electron transfer. Here, we show that in a push-pull type, μ-oxo-bridged porphyrin heterodimer composed of octaethylporphyrinatoaluminum(iii) and octaethylporphyrinatophosphorus(v), the strong excitonic coupling between the porphyrins and the different electron withdrawing abilities of Al(iii) and P(v) promote the formation of a high energy CT state. Using, an array of optical and magnetic resonance spectroscopic methods along with theoretical calculations, we demonstrate photodynamics of the heterodimer that involves the initial formation of a singlet CT which relaxes to a triplet CT state with a lifetime of ∼130 ps. The high-energy triplet CT state (3CT = 1.68 eV) lasts for nearly 105 μs prior to relaxing to the ground state.

Ligand-based mixed valent (MV) complexes of Al(iii) incorporating electron donating (ED) and electron withdrawing (EW) substituents on bis(imino)pyridine ligands (I2P) have been prepared. The MV states containing EW groups are both assigned as Class II/III, and those with ED functional groups are Class III and Class II/III in the (I2P-)(I2P2-)Al and [(I2P2-)(I2P3-)Al]2- charge states, respectively. No abrupt changes in delocalization are observed with ED and EW groups and from this we infer that ligand and metal valence p-orbitals are well-matched in energy and the absence of LMCT and MLCT bands supports the delocalized electronic structures. The MV ligand charge states (I2P-)(I2P2-)Al and [(I2P2-)(I2P3-)Al]2- show intervalence charge transfer (IVCT) transitions in the regions 6850-7740 and 7410-9780 cm-1, respectively. Alkali metal cations in solution had no effect on the IVCT bands of [(I2P2-)(I2P3-)Al]2- complexes containing -PhNMe2 or -PhF5 substituents. Minor localization of charge in [(I2P2-)(I2P3-)Al]2- was observed when -PhOMe substituents are included.

Three anthracene derivatives, referred to as 2-phenyl anthracene (Ph-Ant), 2-thiazole anthracene (TZ-Ant), and 2-pentafluorophenyl anthracene (F5Ph-Ant), were designed and synthesized to reveal the effects of the electron-withdrawing substituents on the molecular packing structure and photoelectric properties of the anthracene core. As the electron-withdrawing abilities of the substituents increased, the molecular structures of the three semiconductors showed a progressive deterioration in intermolecular interactions and molecular accumulation, and the photoelectric properties became worse. Interestingly, the energy levels of the three semiconductors showed gradually decreasing changes with an enhancement of the electron-withdrawing abilities of the substituents, indicating a possible strategy for fabricating n-type anthracene derivative semiconductor materials.

The ability to control the chemical conformation of a system via external stimuli is a promising route for developing molecular switches. For eventual deployment as viable sub-nanoscale components that are compatible with current electronic device technology, conformational switching should be controllable by a local electric field (i.e. E-field gateable) and accompanied by a rapid and significant change in conductivity. In organic chemical systems the degree of π-conjugation is linked to the degree of electronic delocalisation, and thus largely determines the conductivity. Here, by means of accurate first principles calculations, we study the prototypical biphenyl based molecular system in which the dihedral angle between the two rings determines the degree of conjugation. In order to make this an E-field gateable system we create a net dipole by asymmetrically functionalising one ring with: (i) electron withdrawing (F, Br and CN), (ii) electron donating (NH2), and (iii) mixed (NH2/NO2) substituents. In this way, the application of an E-field interacts with the dipolar system to influence the dihedral angle, thus controlling the conjugation. For all considered substituents we consider a range of E-fields, and in each case extract conformational energy profiles. Using this data we obtain the minimum E-field required to induce a barrierless switching event for each system. We further extract the estimated switching speeds, the conformational probabilities at finite temperatures, and the effect of applied E-field on electronic structure. Consideration of these data allow us to assess which factors are most important in the design of efficient gateable electrical molecular switches.

Anions perform several important functions in biological processes. Thus, structures that are able to interact with anions are of great relevance. Here, light is shed on the main characteristics of the bonds between the anions chloride (Cl−), bromide (Br−) and nitrite (NO2−) and the –CH groups of trioxane structures non-substituted and polarized by the ligands (i) –CH3, (ii) –CH2Cl, (iii) –CHCl2, and (iv) –CCl3. There is a less attractive recognition of the anions Cl−, Br− and NO2− using trioxane substituted by the –CH3 groups compared to the receptors non-substituted due to the destabilization of the electrostatic interactions C–H⋯(Cl−, Br− and NO2−). The presence of electron withdrawing groups in the receptor structure improves the interaction with the anions through more favorable σ bonds between the –CH groups and anions Cl−, Br− and NO2−. The anion NO2− is recognized with (i) more favorable and (ii) similar energy and rate by receptors containing (i) –CH3 and (ii) –CH2Cl, –CHCl2 or –CCl3, compared to anions Cl− and Br−. The lower values of the Pauli repulsion contribution in receptors⋯Cl− bonds when compared to the interactions receptors⋯Br− explain the more favorable recognition of the anion Cl− in relation to Br−. The larger recognition rate of the anion Cl− regarding to anion Br− is determined by more favorable electrostatic and orbital interactions. These data provide relevant information about the recognition of anions using C–H bonds and can be used to guide the development of new receptors.

Pummerer reaction is a well-known protocol for α-functionalization of alkyl sulfoxides. However, in contrast to the progress in developing intramolecular variants, the development of intermolecular Pummerer-type C–C coupling reactions has lagged with limited success, which relies heavily on the use of bases and/or Lewis acids. Herein, we demonstrate that difluoroenol silyl ether is an effective C-nucleophile to perform intermolecular Pummerer reaction without any additives, leading to highly selective α-C–H difluoroalkylation of a wide variety of alkyl sulfoxides including drug analogues and natural product derivatives. Mechanistic studies reveal that the success of the reaction originates from the electron withdrawing effect of fluorine in difluoroenol silyl ether which gives it the ability to distinguish different S(IV) species.

Two mononuclear Dy3+ compounds [Dy(bmbpen-F)X] (X = Cl, 1; Br, 2) with a pentagonal bipyramidal (PBP) geometry were obtained from N,N′-bis-(5-methyl-2-hydroxybenzyl)-N,N′-bis(5-fluoro-2-methylpyridyl)ethylenediamine (H2bmbpen-F) and dysprosium halides. The magnetic anisotropy and single-molecule magnet (SMM) behavior of these PBP compounds were regulated by introducing both electron-withdrawing F atoms into the equatorial pyridine rings and electron-donating –CH3 groups into the axial phenolic hydroxyl rings. The results of magnetic characterization show that 1 and 2 exhibit single molecule magnet behavior with magnetization reversal barriers of 990(13) and 1189(16) K under a zero dc external field and magnetic hysteresis loops up to 26 K and 36 K, respectively. The results of ab initio calculations are consistent with the experimental observations, confirming that the simultaneous introduction of electron-withdrawing groups into the equatorial positions and electron-donating groups into the axial positions can lead to PBP Dy-SMMs with improved properties.

We describe a novel mechanism of stabilization of the E-ac isomer of an arylhydrazide via nN → π*Ar interactions. We further show that when a leaving group (F) is present at the ortho-position of the carbonyl group of such an arylhydrazide, the nN → π*Ar interaction facilitates an SNAr autocyclization reaction to produce indazolone, an important heterocycle with biological activity. Faster autocyclization of arylhydrazide is observed when an electron withdrawing group is present in the aryl ring, which is a characteristic of SNAr reactions.

Five new PdII complexes are reported and have been obtained by the reaction of monomeric [Pd(bipy)(py)2]2+, which serves as a builing block, and substituted (ArSe)2 or Pd(SeAr)2. Complexes [Pd2(μ-SeAr)2(bipy)2](PF6)2, Ar = Ph (1), p-ClC6H4 (2), p-FC6H4 (3), [Pd3(μ3-Se)2(bipy)3](PF6)2·5THF (4) and [Pd3(μ-SeMes)4(bipy)2](PF6)2·2MeCN (5) showed that the nuclearity of these structures is affected by electron donating groups (EDGs) and electron withdrawing groups (EWGs) from the selenium-containing ligands, where changing the stoichiometry ratio of the reactants does not affect the number of palladium centers. The distinct behaviors of 1–5 in the solid state, solution phase and gas phase were investigated by single-crystal XRD, NMR and ESI-TOF-MS. In solution, the dinuclear 1–3 structures exist in equilibrium with trinuclear species. In the gas phase, trinuclear and tetranuclear aggregates of 1–3 are detected, as well as dinuclear and tetranuclear aggregates for 5, while compound 4 maintains the same nuclearity. The solid-state electrochemical behavior was studied, and all complexes were electrochemically active, exhibiting irreversible electrochemical processes, where selenium is indicated to be the active species which oxidizes under such conditions. The complexes are potential candidates to act as semiconductor sensitizers for photocatalytic hydrogen evolution, as they absorb in the visible region with optical band gap energies in the range of 2.6 eV.

Trinitromethane moieties are very important for the design and development of high performing dense green oxidizers. The novel oxidizer 1,2-bis(5-(trinitromethyl)-1,2,4-oxadiazol-3-yl)diazene, 14 is stable in water in contrast to 1,2,4-oxadiazoles with other electron withdrawing substituents at the C5-position. Compound 14 is a CNO-based oxidizer with positive oxygen balance (+6.9%), moderate thermostability, and mechanical insensitivity that may find useful applications in the field of green rocket propallant.

Graphitic carbon nitride (CN) is a promising candidate for use in photocatalytic pollutant degradation, but it only shows moderate activity because of its sluggish photocarrier transfer and insufficient light absorption. Herein, CN@DMAP-X (DMAP is 4-dimethylaminopyridine and X is the amount of DMAP) samples were synthesized using a simple polycondensation strategy via grafting DMAP onto the edge of a g-C3N4 framework. The nucleophilic pyridine ring induces the delocalization of the local electrons of the large number of π-bonds, which alters the electron distribution and avoids in-plane carrier recombination. The steric hindrance effects of the 4-dimethylamino groups on DMAP limit the random growth of the g-C3N4 framework and contribute more layered structures, which can enhance visible light absorption via providing more scattering of light, and this can also provide more accessible active sites for the sunset yellow (SY) macromolecule. CN@DMAP-200 showed optimum visible light degradation efficiency toward SY, up to 2.51 times that of pristine g-C3N4. 1O2 was determined to be the dominant active species for SY degradation, whereas ˙O2− and h+ played secondary roles in photodegradation.