Strong Electron-withdrawing Group Research Articles

Tuning the Thermal Stability of Tetra-o-chloroazobenzene Derivatives by Transforming Push-Pull to Push-Push Systems.

Molecular photoswitches provide interesting tools to reversibly control various biological functions with light. Thanks to its small size and easy introduction into the biomolecules, azobenzene derivatives have been widely employed in the field of photopharmacology. All visible-light switchable azobenzenes with controllable thermostability are highly demanded. Based on the reported tetra-o-chloroazobenzenes, we synthesized push-pull systems, by introducing dialkyl amine and nitro groups as strong electron-donating and electron-withdrawing groups on the para-positions, and then transformed to push-push systems by a simple reduction step. The developed push-pull and push-push tetra-o-chloroazobenzene derivatives displayed excellent photoswitching properties, as previously reported. The half-life of the Z-isomers can be tuned from milliseconds for the push-pull system to several hours for the push-push system. The n-π* and π-π* transitions have better resolution in the push-push molecules, and excitation at different wavelengths can tune the E/Z ratio at the photostationary state. For one push-pull molecule, structure and absorption spectra obtained from theoretical calculations are compared with experimental data, along with data on the push-push counterpart.

Designing Novel Solvents for High Voltage Li-Ion Batteries

The pursuit of higher energy density in lithium-ion batteries has led to the development of new cathode materials that can operate at elevated voltages and provide increased specific capacities. [1-2] One such class of materials is the nickel-rich layered oxide cathodes known as LiNixMnyCozO2 (NMC). These cathodes offer high specific capacities and demonstrate electrochemical stability at high cutoff voltages, making them promising candidates for advanced lithium-ion batteries. [3-4] However, NMC cathodes face a significant challenge in the form of capacity fading during cycling. This issue primarily arises from the voltage instability of the conventional carbonate-based electrolytes used in lithium-ion batteries, which are typically designed for the 4-V lithium-ion chemistry. [5-6] As a result, researchers and scientists have directed extensive efforts toward developing new and improved electrolyte systems that can withstand the high voltage requirements of NMC cathodes and other high-energy applications. [7-8]Designing and synthesizing new molecules for use as electrolyte solvents in lithium-ion batteries is indeed a complex and challenging task. Researchers often focus on optimizing one specific property, which can lead to the development of molecules that excel in that aspect while potentially overlooking other crucial features that are necessary for stable battery cycling. For example, the development of α-fluorinated sulfones as electrolyte solvents was driven by their exceptional anodic stability. [9] This stability is achieved by introducing strong electron-withdrawing trifluoromethyl groups directly attached to the sulfonyl group. However, while this electron-withdrawing effect enhances anodic stability, it can also significantly increase the reduction potential of α-fluorinated sulfones. This heightened reduction potential renders them unstable when used with graphite anodes, highlighting the delicate balance required in designing electrolyte solvents that perform well across various aspects of battery operation.In this presentation, we embraced the concept of a "golden middle way" when designing and synthesizing new electrolyte solvents. The recently developed β-fluorinated sulfone, TFPMS, doesn't claim to be the best in any single property, but it strikes a balance across various key characteristics. This equilibrium has proven to be highly effective in ensuring the long-term stability of high-voltage graphite||NMC622 full cells. Positioned at the β site of the sulfone molecule, the strong electron-withdrawing trifluoromethyl group renders β-fluorinated sulfone sufficiently stable against the high-voltage NMC622 cathode, even if it possesses a slightly lower oxidation potential compared to its α-fluorinated counterparts. Furthermore, its reduction potential is lower than that of α-fluorinated sulfone, making it considerably more stable when paired with the graphite anode. While it may not possess the same high lithium solvating power as the typical sulfone (EMS), the lithium solvating capacity of β-fluorinated sulfone falls somewhere in between, mitigating transition metal dissolution and deposition in the graphite||NMC622 full cell that utilizes a β-fluorinated sulfone-based electrolyte. As a result, the full cell equipped with TFPMS-based electrolyte demonstrates superior cycling performance, with a significantly higher average capacity than cells using regular sulfone or α-fluorinated sulfone-based electrolytes. In summary, our approach exemplifies the successful application of the "golden middle way" in designing and synthesizing new electrolyte solvents.Reference: Santhanam, R.; Rambabu, B., Power Sources 2010, 195, 5442.Lin, F.; Markus, I. M.; Nordlund, D.; Weng, T.-C.; Asta, M. D.; Xin, H. L.; Doeff, M. M., Commun. 2014, 5, 3529.Li, W.; Song, B.; Manthiram, A., Chemical Society Reviews 2017, 46 (10), 3006.Xu, J.; Lin, F.; Doeff, M. M.; Tong, W., Journal of Materials Chemistry A 2017, 5 (3), 874.Xia, J.; Petibon, R.; Xiong, D.; Ma, L.; Dahn, J., Journal of Power Sources 2016, 328, 124.Chen, S.; Wen, K.; Fan, J.; Bando, Y.; Golberg, D., Journal of Materials Chemistry A 2018, 6 (25), 11631.Zheng, J.; Lochala, J. A.; Kwok, A.; Deng, Z. D.; Xiao, J., Advanced Science 2017, 4 (8), 1700032.Yamada, Y.; Wang, J.; Ko, S.; Watanabe, E.; Yamada, A., Nature Energy 2019, 4 (4), 269.Su, C.-C.; He, M.; Redfern, P. C.; Curtiss, L. A.; Shkrob, I. A.; Zhang, Z., Environ. Sci. 2017, 10 (4), 900.

Spectral-Sensing System for Distinguishing CH3OH and CD3OD.

Spectrally discriminating CH3OH and CD3OD, and even detecting CH3OH contents in the CD3OD solvent, are important yet have not been achieved so far, likely owing to their very similar chemical/physical properties. Herein, dynamic transesterification reactions, which can be achieved via two-step proton transfers, can be signaled via ultraviolet UV-visible (UV/vis) absorption and fluorescence spectroscopies under mild experimental conditions. Introduction of strong electron-withdrawing groups, such as -NO2, to the aromatic ring (benzoic acid moiety or phenol moiety) of carboxylate esters to activate the esters is important for transesterification reactions and is an intriguing method for modulating the selectivity of the spectral response. The rate constant of the transesterification reaction enhanced with increasing the total number of strong electron-withdrawing groups. Furthermore, the rate constants of esters in which substituent(s) are connected to the phenol moiety are higher than those of corresponding esters in which substituent(s) are connected to the benzoic acid moiety. In transesterification systems, added aliphatic amines mainly play two roles: (i) lowering the energy barrier of the first transesterification step via the formation of intermolecular hydrogen bonding in ternary systems and (ii) deprotonating the released 4-nitrophenol in UV/vis absorption spectral systems to generate an UV/vis absorption spectral signal reporter, i.e., nitrophenolate anions. As a result of the methanol-mediated transesterification reaction, spectral-sensing systems can be established for discriminating CH3OH and CD3OD and even detecting low CH3OH contents in the CD3OD solvent, owing to the kinetic isotope effect. This is the first example of spectral recognition between CD3OD and CH3OH.

Push-Pull Carbazole-Based Dyes: Synthesis, Strong Ultrafast Nonlinear Optical Response, and Effective Photoinitiation for Multiphoton Lithography.

The present work reports on the ultrafast nonlinear optical (NLO) properties of a series of D-π-Α and D-A push-pull carbazole-based dyes and establishes a correlation between these properties and their efficiency for potential photonic and optoelectronic applications such as multiphoton lithography (MPL). The ultrafast NLO properties of the studied dyes are determined by two distinct experimental techniques, Z-scan and pump-probe optical Kerr effect (OKE), employing 246 fs laser pulses at 515 nm. The results indicate that chemical functionalization of the carbazole moiety with various strong electron-donating and/or electron-withdrawing groups, such as benzene, styrene, 4-bromostyrene, nitrobenzene, trimethyl isocyanurate, methyl, and indane-1,3-dione, can result in a controlled and significant enhancement of the NLO absorptive and refractive responses. In the context of potential applications, the efficiency of carbazole-based organic materials as photoinitiators (PIs) for MPL applications is demonstrated. The fabricated woodpile microstructure using chemically functionalized carbazole as a PI demonstrates improvements in both feature size and MPL efficiency compared to that using unfunctionalized carbazole as a PI. This is attributed to the efficient charge transfer resulting from chemical functionalization, which leads to a substantial increase (approximately 1 order of magnitude) in the values of the imaginary part of the second-order hyperpolarizability (Imγ) and the two-photon absorption cross section (σ). The achieved feature size of 280 nm is comparable to that obtained with other widely used PIs in MPL applications. Additionally, owing to the strong NLO properties of the studied functionalized carbazole, they could also be promising candidates for further applications in photonics and optoelectronics.

Enhanced mineralization of nitrophenols by a novel C@ZVAl-PS based sequential reduction-oxidation process

Widely employed nitrophenols (NPs) are refractory and antioxidant due to their strong electron-withdrawing group (-NO2). Actually, NPs are readily reduced to aminophenols (APs). However, APs remain toxic and necessitate further treatment. Herein, we utilized a novel sequential reduction-oxidation system of carbon-modified zero-valent aluminum (C@ZVAl) combined with persulfate (PS) for the thorough removal of both NPs and APs. The results demonstrated that p-nitrophenol (PNP, up to 1000 mg/L) exhibited complete reduction to p-aminophenol (PAP), and then over 98.0 % of PAP could be effectively oxidized, in the meantime the removal rate of chemical oxygen demand (COD) was as high as 95.9 %. Based on the SEM and XPS characterizations, we found that C@ZVAl has exceptionally high reactivity that generates massive electrons and reduces PNP to PAP through accelerated electron transfer. In the subsequent oxidation step, PS can be rapidly activated by C@ZVAl to generate SO4− radicals for PAP oxidization. Meanwhile, the mineralization of COD proceeds. The temporal binding of reduction and oxidation can be regulated by varying the PS dosing time. Namely, the appropriate delay in PS dosing facilitates sufficient reduction to provide enough reactants for oxidation, favoring the mineralization of PNP and COD. More crucially, dinitrodiazophenol (DDNP) in an actual explosive wastewater without any pretreatment can be effectively mineralized by this sequential reduction-oxidation system, affirming the excellent performance of this process in practical applications. In conclusion, the C@ZVAl-PS based sequential reduction-oxidation looks very promising for enhanced mineralization of nitro-substituted organic contaminants.

Theoretical study on the effect of different positions of -CN group on photophysical properties and forward-reverse ESIPT behaviours of 2,5-bis(benzo[d]thiazol-2-yl)phenol derivatives

Excited state intramolecular proton transfer (ESIPT) compounds have been widely used in many fields due to its unique photophysical properties, but they are strongly affected by substituents. There are many studies on the effect of substituents at the same position on the ESIPT process, but there are few studies on the effects of substituents at different positions on the proton transfer process. In this work, a strong electron-withdrawing cyano group ( – CN) was introduced into different positions of 2,5-bis(benzo[d]thiazol-2-yl)phenol. The effect of different substituted positions on intramolecular hydrogen bond (IHB), photophysical properties and forward-reverse energy barrier of ESIPT reaction have been systematically investigated adopting density functional theory (DFT) and time-dependent DFT. The result showed that the introduction of – CN group at different positions led to a slight red-shift of absorption, and intramolecular charger transfer is the intrinsic reason for this photophysical phenomenon. The position of – CN group obviously influenced the excited state IHB, and then had an effect on ESIPT process. The substitution positions in the left benzo[d]thiazole ring and phenol ring respectively hinder and promote the ESIPT process, while the substitution in the right benzo[d]thiazole ring not only impetus the ESIPT process, but also increase the tautomer fluorescence.

The oxidation of 2-phenyl ethanols by Fe(NO3)3·9H2O in CF3COOH: The dramatic substituent effect

2-Phenyl ethanol with various substituents on the phenyl ring was oxidized by Fe(NO3)3·9H2O in the present of trifluoroacetic acid (TFA) at 0°C to room temperature. The product was highly dependent on the electronic properties of the substituent. Weak electron-donating and electron-withdrawing groups (Such as CH3, Cl, Br, and F) afforded good to excellent yields (95 – 64 %) of the corresponding phenylacetic acids. Moderate electron-withdrawing groups (Such as CF3, COOH) resulted in ∼ 50 % yield of the corresponding phenylacetic acids. However, strong electron-withdrawing group (such as NO2 and CN) hindered the reaction, the corresponding phenethyl trifluoroacetate was acquired almost quantitatively. Furthermore, the strong electron-donating group of methoxy highly promoted the oxidation, resulted in nitrated benzaldehydes and benzoic acids in relative low yields.

Aramid-Reinforced UV Curable Adhesive Resins for Use As an Interlayer in Laminated Glass.

Colorless, transparent, and mechanically robust aramid polymers are synthesized from two diamine monomers with strong electron-withdrawing groups, using low-temperature solution condensation with diacid chloride. The aramids dissolved very well in the liquid acrylamide monomers. When N,N-dimethylacrylamide (DMA) is used as a reactive diluent, films with the desired features are produced from the hybrid aramid-DMA resins via ultraviolet (UV)curing. The hybrid films are colorless and transparent in the visible region and showed an increase in the glass transition temperature, tensile strength, and elastic modulus in proportion to the aramid content. Laminated glass is manufactured using the hybrid resin as an interlayer, which exhibits very strong adhesion between the two sheets of glass, is not easily broken by an external impact, and do not scatter fragments. Moreover, the laminated glass do not distort images and functioned very effectively in UV blocking, soundproofing, and suppressing changes in the ambient temperature. Heat treatment further improves the light transmittance and impact resistance of the laminated glass. Laminated glass specimens with various fluorescence colors are also manufactured. Aramid-reinforced films prepared using N,N-diethylacrylamide as a reactive diluent underwent thermally induced phase separation in a wet state, providing smart glass with a privacy protection function.

Stable Lithium Oxygen Batteries Enabled by Solvent-diluent Interaction in N,N-dimethylacetamide-based Electrolytes.

In the pursuit of next-generation ultrahigh-energy-density Li-O2 batteries, it is imperative to develop an electrolyte with stability against the strong oxidation environments. N,N-dimethylacetamide (DMA) is a recognized solvent known for its robust resistance to the highly reactive reduced oxygen species, yet its application in Li-O2 batteries has been constrained due to its poor compatibility with the Li metal anode. In this study, a rationally selected hydrofluoroether diluent, methyl nonafluorobutyl ether (M3), has been introduced into the DMA-based electrolyte to construct a localized high concentration electrolyte. The stable -CH3 and C-F bonds within the M3 structure could not only augment the fundamental properties of the electrolyte but also fortify its resilience against attacks from O2- and 1O2. Additionally, the strong electron-withdrawing groups (-F) presented in the M3 diluent could facilitate coordination with the electron-donating groups (-CH3) in the DMA solvent. This intermolecular interaction promotes more alignment of Li+-anions with a small amount of M3 addition, leading to the construction of an anion-derived inorganic-rich SEI that enhances the stability of the Li anode. As a result, the Li-O2 batteries with the DMA/M3 electrolyte exhibit superior cycling performance at both 30 °C (359th) and -10 °C (120th).

Synthesis and Characterization of Octacyano-Cu-Phthalocyanine.

Octacyano-metal-substituted phthalocyanine MPc(CN)8 is a promising n-type stable organic semiconductor material with eight cyano groups, including a strong electron-withdrawing group at its molecular terminals. However, most MPc(CN)8 have not been thoroughly investigated. Therefore, CuPc(CN)8 was synthesized in this study and its crystal structure, chemical and electronic states, thermal stability, and electrical properties were investigated. This article discusses the various properties of CuPc(CN)8, as compared to those of CuPc and FePc(CN)8. The previously reported FePc(CN)8 is an organic semiconductor molecule with a molecular structure similar to that of CuPc(CN)8. X-ray diffraction (XRD) measurements revealed that CuPc(CN)8 has a crystalline structure in the P1̅ space group. The crystal structure forms an in-plane network parallel to the molecular plane through multiple hydrogen bonds by the cyano groups at the molecular terminals. Interestingly, the crystal structure, especially the molecular stacking, of CuPc(CN)8 differs from that of FePc(CN)8. The absorption edge observed in the ultraviolet-visible spectrum of CuPc(CN)8 shifted to a longer wavelength than that of CuPc, which was attributed to the energy gap of CuPc(CN)8 being smaller than that of CuPc owing to the influence of the cyano groups at the molecular terminals, according to the molecular orbital calculation results using density functional theory. Ultraviolet photoelectron spectroscopy measurements confirmed that CuPc(CN)8 had a stronger n-type character than CuPc because of the orbital energy stabilization by the cyano groups. Thermogravimetry/differential thermal analysis measurements revealed that the thermal stability of CuPc(CN)8 was significantly higher than that of FePc(CN)8. CuPc(CN)8 exhibited photoconduction upon visible-light irradiation, and its electrical conductivity was higher than that of CuPc, which was attributed to a reduction in the electron injection barrier at the electrode interfaces.

Bis(imino)pyridyliron incorporated with NO2, F and benzhydryl substituents as thermostable precatalysts for vinyl-terminated polyethylenes

The electronic and steric properties of ligands are of great importance in late transition metal catalyst mediated ethylene polymerization to tune the catalytic performance. In this contribution, strong electron-withdrawing groups—fluoro and nitro—along with benzhydryl as a steric component, were incorporated into the parent bis(imino)pyridine ligand structure to prepare a series of iron (II) chloride complexes: 2-[MeC=N{2-(Ph2CH)-4-NO2-6-F}C6H2]-6-[MeC=N(Ar)C6H2]C5H3N–FeCl2 (Ar = 2,6-Me2C6H3Fe2Me, 2,6-Et2C6H3Fe2Et, 2,6-iPr2C6H3Fe2iPr, 2,4,6-Me3C6H2Fe3Me and 2,6-Et2-4-MeC6H2Fe2Et,Me). Apart from the structural characterization of all complexes executed via FTIR and elemental analysis, X-ray diffraction analysis unveiled distorted square pyramidal geometry for Fe2Me (τ5 = 0.21) and Fe2Et (τ5 = 0.28). Upon in situ activation with either MAO or MMAO cocatalysts, all iron complexes displayed distinguished polymerization performance, especially in terms of thermo-stability. In particular, the less hindered Fe2Me exhibited high activity: 20.4 × 106 g mol−1 h−1 at 70 °C, 1.5 × 106 g mol−1 h−1 at 110 °C, and 0.6 × 106 g mol−1 h−1 at 120 °C. Whereas, the sterically more hindered Fe2iPr proved to be more productive in generating high molecular weight polyethylene (Mw up to 410.7 kg mol−1 at 70 °C). Moreover, by adjusting the reaction temperature and ligand structure, the chain termination reaction could be modulated from a high proportion of vinyl-terminated polyethylene to saturated polyethylene rich product [CH2CH(CH2)nCH3/CH3(CH2)nCH3 = 0.7/0.3–0.39/0.61], as confirmed by high-temperature 1H/13C NMR spectra. Low molecular weight vinyl-terminated polyethylenes are of significant importance in the synthesis of functional polymers and can serve as valuable additives in lubricants.

Local charge redistribution enables single ionic conductor for fast charge solid Li battery

Solid polymer electrolytes (SPEs) have been regarded as hopeful candidate electrolyte for solid-state lithium battery. However, the low Li+ transference number and poor interface stability pose great challenges for the high rate capability of SPE. Herein, inspired from the density functional theory (DFT) calculations that local positive charge distribution can be regulated by introducing strong electron-withdrawing groups, which can selectively anchor TFSI−, largely enhance the Li+ transference number. As predicted, the obtained CPE-NO2 deliver a remarkable Li+ transference number of 0.91, equal to a single-ion conductor for Li+, largely high than that of the SPE (0.31), according well with the molecular dynamics (MD) simulations and pyridine complexation experiments. Furthermore, the PEO||Li interfacial stability, flame retardant ability, and mass transfer of Li+ in interface can also be largely enhanced by interfacial by-product, which are fast Li+ conductors according to TOF-SIMS results. Impressively, the Li|CPE-NO2|Li cell exhibit superior cyclability for 2200 h at 0.1 mA cm−2, and the solid LFP|CPE-NO2|Li battery delivers prominent capacity of 127.4 mAh g−1 at a high rate 5 C (12 mins). This work breaks the fast charge limitation of solid lithium battery, and provides a feasible approach for the construction of advanced solid electrolyte.

Afterglow Performance of Phenylenevinylene-Based Semiconducting Polymer Nanoparticles Doped with Photosensitizers Containing Electron-Withdrawing Groups.

It is usually believed that doping with photosensitizers capable of generating singlet oxygen (1O2) plays a pivotal role in enhancing the afterglow performance of semiconducting polymer nanoparticles (SPNs). However, the effect of doping photosensitizer bearing electron-withdrawing groups has not been reported. Here we report the effect of doping with six photosensitizers possessing different electron-withdrawing groups on the afterglow performance of SPNs using poly[(9,9-di(2-ethylhexyl)-9H-fluo-rene-2,7-vinylene)-co-(1-methoxy-4-(2-ethylhexyloxy)-2,5-phenylenevinylene)] (PF-MEHPPV) as substrate. It was found that the afterglow performance of SPNs was significantly influenced by doping with photosensitizers bearing electron-withdrawing groups. For the doped photosensitizers with strong electron-withdrawing groups, the stronger the electron-withdrawing ability of the group, the worse of the afterglow performance of the SPN regardless of the 1O2 generation ability of the photosensitizer. When the doped photosensitizer exhibited weak or none electron-withdrawing effect, the 1O2 generation ability of the photosensitizer played a dominant role on the afterglow performance of the SPNs. This work deepens the understanding of the design and synthesis of SPNs with different afterglow properties.

Robust Radicals Featuring B- and N-Embedded Dioxygen-Bridged Units: Synthesis, Structures, and Optical Properties.

Tris(2,4,6-trichlorophenyl)methyl (TTM) group has been widely used for constructing organic radicals, but the poor optical stabilities limit the application prospects of the TTM radicals. In this work, the rigid B- and N-embedded dioxygen-bridged (BO and NO) units were attached to the TTM skeleton as the strong electron-withdrawing and electron-donating groups, respectively. The rigidity and strong electronic effect of the BO and NO units contribute to the high chemical and optical stability of BO-TTM and NO-TTM radicals. Notably, NO-TTM exhibits near-infrared emission at 830 nm with a narrow full width at half maximum (FWHM) of 55 nm (100 meV), while BO-TTM shows blue-shifted luminescence at 635 nm and a narrower FWHM of merely 43 nm (130 meV). This study has developed a methodology to produce highly efficient and enduring luminescent radicals, which could tune emission properties such as wavelength and FWHM.

Theoretical Investigation on Dialumenes toward Dihydrogen Activation: Mechanism and Ligand Effect.

Herein, we report a computation study based on the density functional theory calculations to understand the mechanism and ligand effect of the base-stabilized dialumenes toward dihydrogen activation. Among all of the examined modes of dihydrogen activation using the base-stabilized dialumene, we found that the concerted 1,2-hydrogenation of the Al═Al double bond is kinetically more preferable. The concerted 1,2-hydrogenation of the Al═Al double bond adopts an electron-transfer model with certain asynchrony. That is, the initial electron donation from the H-H σ bonding orbital to the empty 3p orbital of the Al1 center is followed by the backdonation from the lone pair electron of the Al2 center to the H-H σ antibonding orbital. Combined with the energy decomposition analysis on the transition states of the concerted 1,2-hydrogenation of the Al═Al double bond and the topographic steric mapping analysis on the free dialumenes, we ascribe the higher reactivity of the aryl-substituted dialumene over the silyl-substituted analogue in dihydrogen activation to the stronger electron-withdrawing effect of the aryl group, which not only increases the flexibility of the Al═Al double bond but also enhances the Lewis acidity of the Al═Al core. Consequently, the aryl-substituted dialumene fragment suffers less geometric deformation, and the orbital interactions between the dialumene and dihydrogen moieties are more attractive during the 1,2-hydrogenation process. Moreover, our calculations also predict that the Al═Al double bond has a good tolerance with the stronger electron-withdrawing group (-CF3) and the weaker σ-donating N-heterocyclic carbene (NHC) analogue (e.g., triazol carbene and NHSi). The reactivity of the dialumene in dihydrogen activation can be further improved by introducing these groups as the supporting ligand and the stabilizing base on the Al═Al core, respectively.

The mechanism and origins of the chemo- and regio-selectivity of ruthenium porphyrin catalyzed C[sbnd]H bonds oxidation

Selective functionalization of polymers derived from branched alkane monomers is extremely challenging due to the low reactivity of CH bonds and uncontrolled depolymerization. In this work, the chemoselective and regioselective catalytic oxygenation mechanism of hydrocarbons with ruthenium porphyrin complexes and aromatic N-oxides was investigated by density functional theory (DFT) calculations. The results revealed that the oxoruthenium porphyrin species with remarkable reactivity as oxygen transfer agents is responsible for the hydrogen abstraction from CH bonds followed by fast hydroxyl radical rebound. Details regarding the calculations of various oxidation processes show that the regioselectivity is related to the intrinsic strength of different CH bonds in branched alkanes and the charge transfer of the hydrogen atom transfer (HAT) step. Comparing the oxidations of branched alkanes to alcohols and ketones, the chemoselectivity is attributed to the relative barriers of HAT pathways in the two-step oxidation stage. Finally, the substituent effects of fluorine in the porphyrin ligand are elucidated and a stronger electron-withdrawing group is predicted to promote the HAT process and regulate hydroxyl radical rebound, ultimately enabling more efficient oxidation. These findings provide relevant information for understanding the selective oxidation of polyolefins through transition metal catalysis and enzymatic catalysis.

Functionalized Phenanthrene Imide-Based Polymers for n-Type Organic Thin-Film Transistors.

High-performing n-type polymers are crucial for the advance of organic electronics field, however strong electron-deficient building blocks with optimized physicochemical properties for constructing them are still limited. The imide-functionalized polycyclic aromatic hydrocarbons (PAHs) with extended π-conjugated framework, high electron deficiency and good solubility serve as promising candidates for developing high-performance n-type polymers. Among the PAHs, phenanthrene (PhA) features a well-delocalized aromatic π-system with multiple modifiable active sites . However, the PhA-based imides are seldom studied, mainly attributed to the synthetic challenge. Herein, we report two functionalized PhAs, CPOI and CPCNI, by simultaneously incorporating imide with carbonyl or dicyanomethylene onto PhA. Notably, the dicyanomethylene-modified CPCNI exhibits a well stabilized LUMO energy level (-3.84 eV), attributed to the synergetic inductive effect from imide and cyano groups. Subsequently, based on CPOI and CPCNI, two polymers PCPOI-Tz and PCPCNI-Tz were developed. Applied to organic thin-film transistors, owing to the strong electron-deficiency of CPCNI, polymer PCPCNI-Tz shows an improved electron mobility and largely decreased threshold voltage compared with PCPOI-Tz. This work affords two structurally novel electron-deficient building blocks and highlights the effectiveness of dual functionalization of PhAs with strong electron-withdrawing groups for devising n-type polymers.

Preparation and Properties of Mechanically Robust, Colorless, and Transparent Aramid Films.

In this study, various diamine monomers were used to synthesize aramid polymer films via a low-temperature solution condensation reaction with diacid chloride. For diamines with relatively high basicity, the reaction system became opaque because amine salt formation inhibited polymer synthesis. Meanwhile, low-basicity diamines with strong electron-withdrawing groups, such as CF3 and sulfone, were smoothly polymerized without amine salt formation to provide highly viscous solutions. The acid byproduct HCl generated during polymerization was removed by adding propylene oxide to the reaction vessel and converting the acid into highly volatile inert substances. The resulting solutions were used as varnishes without any additional purification, and polymer films with an excellent appearance were easily obtained through a conventional casting and convection drying process. The films neither tore nor broke when pulled or bent by hand; furthermore, even when heated up to 400 °C, they did not decompose or melt. Moreover, polymers prepared from 2,2-bis(trifluoromethyl)benzidine (TFMB) and bis(4-aminophenyl)sulfone (pAPS) did not exhibit glass transition until decomposition. The prepared polymer films showed a high elastic modulus of more than 4.1 GPa and a high tensile strength of more than 52 MPa. In particular, TFMB-, pAPS-, and 2,2-bis(4-aminophenyl)hexafluoropropane-based polymer films were colorless and transparent, with very high light transmittances of 95%, 96%, and 91%, respectively, at 420 nm and low yellow indexes of 2.4, 1.9, and 4.3, respectively.

Defect and nanostructure engineering of polymeric carbon nitride for visible-light-driven CO2 reduction

Sunlight-induced photocatalytic carbon dioxide (CO2) reduction to energy-rich chemicals by metal-free polymeric carbon nitride (CN) semiconductor is a promising tactic for sustained solar fuel production. However, the reaction efficiency of CO2 photoreduction is restrained seriously by the rapid recombination of photogenerated carriers on CN polymer. Herein, we incorporate 2-aminopyridine molecule with strong electron-withdrawing group into the skeleton edge of CN layers through a facile one-pot thermal polymerization strategy using urea as the precursor, which renders a modified carbon nitride (ACN) with extended optical harvesting, abundant nitrogen defects and ultrathin nanosheet structure. Consequently, the ACN photocatalyst with desirable structural features attains enhanced separation and migration of photoexcited charge carriers. Under visible light irradiation with Co(bpy)32+ as a cocatalyst, the optimized ACN sample manifests a high CO2 deoxygnative reduction activity and high stability, providing a CO yielding rate of 17 μmol h−1, which is significantly higher than that of pristine CN. The key intermediates engaged in CO2 photoreduction reaction are determined by the in situ diffuse reflectance infrared Fourier transform spectroscopy, which sponsors the construction of the possible photocatalytic CO2 reduction mechanism on ACN nanosheets.

Investigating the Effects of Fluorine Substituents on Organic Dyes in Dye-Sensitized Solar Cells

We synthesized and evaluated five organic dyes that featured both mono- and di-substituted fluorine atoms for application in dye-sensitized solar cells (DSSCs). The dye structure was designed with N, N-dimethylaniline as a donor, fluorophenyl as an π-conjugated bridge, and cyanoacetic acid as an anchoring and acceptor group. The fluorine substituents are strong electron-withdrawing groups, introducing different numbers and positions of fluorine atoms (ortho and meta) that were expected to the ability of the acceptor parts of the dye. The results showed that adding the fluorine mono-substitution in the ortho position can enhance the efficiency of the solar cells in comparison with the meta-substitution and unsubstituted one. However, the di-substitution by fluorine atoms in two ortho positions and ortho, meta positions reduced the performance of the solar cells. The reason was related to the effect of π-conjugation between the fluorine substituent and the carbonyl group of the carboxylic acid. The DSSCs based on dye 14 achieved the best results with power conversion efficiency (PCE) = 3.33%, (Jsc = 5.43 mA cm-2, Voc = 0.81V and FF = 75.85%) under standard conditions with I3-/I- as the electrolyte.