Introduction Of Electron-donating Groups Research Articles

Effects of substitution and conjugation on photophysical properties of ESIPT-based fluorophores with the core of 4-aminophthalimide

4-Aminophthalimide is a highly fluorescent signaling unit with excellent photophysical properties and wide application foregrounds. Based on this, a range of theoretical investigations are conducted on the fluorescent probe (E)-5-((2-hydroxybenzylidene) amino) isoindoline-1, 3-dione (HID) with the core of 4-aminophthalimide using density functional theory (DFT) and time-containing density functional theory (TD-DFT) methods in this paper. The optimized configurations, vertical excitation and emission energies, electronic characteristics and excited-state intramolecular proton transfer (ESIPT) behaviors of the probe HID are discussed in detail. Furthermore, to enhance the luminescent properties of HID, five novel compounds have been designed based on the structure of HID by introducing amino, methoxy and naphthalene groups (–NH2, –OMe and C10H8). Our work thoroughly explores how the property and position of substituents and conjugation affect photophysical characteristics and ESIPT processes. We find that the ESIPT dynamics can be modulated by the substitution and conjugation effects. Specifically, the introduction of amino and methoxy groups at the ortho-position and the introduction of the naphthalene group promote the ESIPT behavior of HID1, whereas the introduction of amino and methoxy groups at the meta-position exhibits the contrary impact. Therefore, we boldly infer that the introduction of electron-donating groups in the ortho-position and the introduction of the conjugated group make the ESIPT process more effortless to occur, whereas the introduction of substituents with opposing natures in the meta-position makes the ESIPT process more difficult to occur. In addition, the ionization potentials (IP), electron affinities (EA) and reorganization energies (λh and λe) of molecules are calculated to assess their potential as luminescent materials. Our work not only reveals the luminescence and ESIPT mechanism of the probe HID1, but also proposes to modulate the ESIPT process through the substitution and conjugation effects. In particular, the designed molecules have better photoelectric properties as a result of their red-shifted absorption and fluorescence spectra, smaller energy gaps, larger transferred charges and greater charge transferred distances, which offers some valuable ideas for the experimental development of more efficient organic luminescent materials with ESIPT properties.

Neutral Nazarov reaction using protic solvents as activators

Abstract Herein, we report a neutral Nazarov reaction using protic solvents instead of strong acids as activators. The key to the success of this reaction lies in the rational design of the divinyl ketone substrates. In particular, the introduction of electron-donating groups (EDGs) at the β- and β′-positions of the carbonyl group in the divinyl ketone increases the Lewis basicity dramatically, an EDG at α-position promotes the cyclization, and the presence of a phenoxy group at β-position enables the irreversible elimination of phenol from the cyclized intermediate, thus shifting the reversible cyclization to the product side. This phenol-releasing reaction can be applied to clip chemistry to target acidic biological environments.

Enhancement of Near-Infrared Emission Based on Hypervalent Germanium(IV)-Fused Azobenzene Compounds with Electron-Donating Groups

Abstract NIR-light emitting materials are significant as a source for NIR-light technology. Previously, we have found that hypervalent germanium-fused azobenzene (GAz) compounds showed NIR emissions despite the small π-conjugated systems owing to trigonal bipyramidal geometry with three-center four-electron (3c-4e) bonds. Herein, we succeed in enhancing their luminescence properties by introduction of electron-donating groups. It is revealed that the frontier molecular orbitals of the π-conjugated systems with the hypervalent bonds can be varied depending on the type of substituents. As a result, a GAz compound with diphenylamine groups shows efficient NIR emission at room temperature (λPL = 761 nm and ΦPL = 0.07) and at 77 K (λPL = 749 nm and ΦPL = 0.20). Furthermore, data from theoretical calculations support the experimental results and provide additional information on the producibility of the hypervalent compounds. Our findings afford strategies to expand the library of the fine-tunable NIR-luminescent materials involving heteroatoms.

Co-assembled Nanocarriers of De Novo Thiol-Activated Hydrogen Sulfide Donors with an RGDFF Pentapeptide for Targeted Therapy of Non-Small-Cell Lung Cancer.

Hydrogen sulfide releasing agents (or H2S donors) have been recognized gasotransmitters with potent cytoprotective and anticancer properties. However, the clinical application of H2S donors has been hampered by their fast H2S-release, instability, and lack of tumor targeting, despite the unclear molecular mechanism of H2S action. Here we rationally designed an amphiphilic pentapeptide (RGDFF) to coassemble with the de novo designed thiol-activated H2S donors (CL2/3) into nanocarriers for targeted therapy of non-small-cell lung cancer, which has been proved as a one-stone-three-birds strategy. The coassembly approach simply solved the solubility issue of CL2/3 by the introduction of electron-donating groups (phenyl rings) to slow down the H2S release while dramatically improving their biocompatible interface, circulation time, slow release of H2S, and tumor targeting. Experimental results confirmed that as-prepared coassembled nanocarriers can significantly induce the intrinsic apoptotic, effectively arrest cell cycle at the G2/M phase, inhibit H2S-producing enzymes, and lead to mitochondrial dysfunction by increasing intracellular ROS production in H1299 cells. The mouse tumorigenesis experiments further confirmed the in vivo anticancer effects of the coassembled nanocarriers, and such treatment made tumors more sensitive to radiotherapy then improved the prognosis of tumor-bearing mice, which holds great promise for developing a new combined approach for NSCLC.

Colorimetric and photoluminescent probes based on iridium(III) complexes for highly selective detection of homocysteine

As a biological thiol closely related to the incidence of gastric cancer, homocysteine (Hcy) has been reported to be detected in vivo and in vitro. The design of ratiometric photoluminescent probes often relies on the unique chemical structure of the molecular. In this paper, we designed and synthesized three aldehyde-containing iridium(III) complexes and characterized their structure and photophysical properties. They showed a good specificity for Hcy detection. The color of the solution gradually changed from red to pale yellow. The photoluminescent variation from red to green was observed by the naked eye after addition of Hcy to the solution of the Ir1 ([(CHO-pba)2Ir(bpy-2NH2)]PF6), Ir2 ([(CF3-pba)2Ir(bpy-2NH2)]PF6) and Ir3 ([(CH3-pba)2Ir(bpy-2NH2)]PF6) with a large blue shift by 120, 63 and 106 nm, respectively. Based on the differences in their structures, it could be inferred that this type of ratiometric photoluminescent probe based on iridium(III) complexes with aldehyde was related to the strong electron-donating effect of the nitrogen-containing substituents on the bipyridine ligand in the structure, and the introduction of electron-donating groups on the 4-(2-pyridinyl)benzaldehyde (pba) ligand can enlarge the blue shift of the photoluminescent wavelength upon sensing of Hcy. On the other hand, iridium(III) complexes are currently recognized as a third-generation good photodynamic therapy photosensitizer. The photodynamic therapy properties of the three iridium(III) complexes in this article have also been evaluated. All of them have strong singlet oxygen generation ability and low cytotoxicity which are expected to be used in photodynamic therapy and Hcy detection.

SYNTHESIS AND PHOTOCHEMICAL PROPERTIES OF NEW STYRYLQUINOLINE-CONTAINING POLYMERS

Compounds 1a, 1b and 5c, 5d were obtained by Knoevenagel condensation with the corresponding aromatic aldehydes during 14 hours. The new methacrylic monomers with styrylquinoline containing moiety were synthesized by reaction the alcohols with methacryloyl chloride. Polymers were synthesized by free radical polymerization. Polymerization ability was investigated and kinetic parameters were determined for compounds 2a, 2b and 6c, 6d during thermoinitiated homopolyme­rization. Polymerization was carried out for 10% solutions of monomers in DMF at 80 °C in argon atmosphere with 1% AIBN. Polymers were characterized by 1HNMR spectroscopy. The speed of polymerization of all new mono­mers was higher than for MMA and phenyl methacrylate due to the effect of the substi­tuent in the p-position of the aromatic ring of the styrylquinoline fragment. In addition, the speed of polymerization increased due to the donor effect of the substituent. It was established that the speed of polymerization for 2b is higher than for monomer 2a. It is possible that decrease in the speed of polymerization occurs due to the substituent, which exhibits electron-accepting properties and can be a trap for free radicals. The results of photochemical and optical activities of the corresponding po­lymers are presented. Investigations of the absorption spectra of the synthesized polymers prove that the optically active styrylquinoline fragment in the polymers is preserved. Thus the photochemical properties of the new po­lymers will correspond to the properties of styrylquinoline-containing compounds. It was established that the introduction of electron-donating groups in the styrylquinoline fragment leads to a bathochromic shift of the absorption spectrum. Changes in absorption maxima during UV irradiation of compound 3a demonstrate photoinduced trans-cis isomerization. From the obtained and presented results, it can be concluded that polymers with styrylquinoline and iminostyrylquinoline fragments can be considered as promising materials for creating materials based on them that require photosensitivity in a certain range of wavelengths.

Identification of a Novel Inhibitor of TfR1 from Designed and Synthesized Muriceidine A Derivatives.

The transferrin receptor 1 (TfR1) plays a key role in cellular iron uptake through its interaction with iron-bound Tf. TfR1 is often reported to be overexpressed in malignant cells, and this increase may be associated with poor prognosis in different types of cancer, which makes it an attractive target for antitumor therapy. The marine natural product Muriceidine A is a potent anticancer agent reported in our previous work. In this study, we designed and synthesized a series of Muriceidine A derivatives and described the systematic investigation into their cytotoxic activities against four tumor cells. Most of the derivatives showed stronger antitumor activity and we found that the introduction of electron-donating groups at position C-2 of unsaturated piperidine was beneficial to anticancer activity and unsaturated piperidine was responsible for the antiproliferative activity. Among these compounds, 12b (methyl at position C-2 of unsaturated piperidine) exhibited the strongest cytotoxicity against MDA-MB-231 cells. Further pharmacological research showed that 12b bound to Transferrin receptor 1 (TfR1) directly caused iron deprivation and ROS imbalance along with the degradations of several oncoproteins, especially FGFR1, through the proteasome pathway; thus, inducing cell cycle arrest and apoptosis in MDA-MB-231 breast cancer cells. Our findings indicate that 12b is a promising lead compound targeting TfR1 for triple negative breast cancer.

Efficient gaseous iodine capture enhanced by charge-induced effect of covalent organic frameworks with dense tertiary-amine nodes

Based on the outstanding application advantages of nitrogen-rich materials with regular porous frameworks in the capture of gaseous radioactive iodine, a series of covalent organic frameworks (COFs) with dual channels and abundant tertiary-amine active sites were constructed herein via a unique multi-nitrogen node design. The high density of up-to-six nitrogen adsorption sites in a single structural unit of the products effectively improved the adsorption capacities of the materials for iodine. Moreover, the adsorption affinity of the active sites can be further regulated by charge-induced effect of different electron-donating groups introduced into the COFs. Adsorption experiments combined with DFT theoretical calculations confirmed that the introduction of electron-donating groups can effectively increase the electron density around the active sites and enhance the binding energy between the materials and iodine, and thus improve the iodine adsorption capacity to 5.54 g/g. The construction strategy of multi-nitrogen node and charge-induced effect proposed in this study provides an important guidance for the study of the structure-activity relationship of functional materials and the design and preparation of high-performance iodine adsorption materials.

Acetylene Derivatives of Cationic Diazaoxatriangulenes and Diaza [4]Helicenes ‐ Access to Red Emitters and Planar Chiral Stereochemical Traits

Cationic triangulenes, and related helicenes, constitute a rich class of dyes and fluorophores, usually absorbing and emitting light at low energy, in the orange to red domains. Recently, to broaden the scope of applications, regioselective late‐stage functionalizations on these core moieties have been developed. For instance, with the introduction of electron‐donating groups (EDGs), important bathochromic shifts are observed pushing absorptions towards or in the near‐infrared (NIR) spectral domain while emissive properties disappear essentially completely. Herein, to upset this drawback, acetylene derivatives of cationic diazaoxa triangulenes (DAOTA) and [4]helicenes are prepared (16 examples). Contrary to other EDG‐functionalized derivatives, C≡C− functionalized products remain broadly fluorescent, with red‐shifted absorptions (Δλ abs up to 25 nm) and emissions (Δλ em up to 73 nm, Φ PL up to 51 %). Quite interestingly, a general dynamic stereoisomerism phenomenon is evidenced for the compounds derived from achiral DAOTA cores. At low temperature in 1H NMR spectroscopy (218 K), N−CH2 protons become diastereotopic with chemical shifts differences (Δδ) as high as +1.64 ppm. The signal coalescence occurs around 273 K with a barrier of ∼12 kcal mol−1. This phenomenon is due to planar chiral conformations (S p and R p configurations), induced by the geometry of the alkyl (n‐propyl) side‐chains next to the acetylenic substituents. Ion pairing studies with Δ‐TRISPHAT anion not only confirm the occurrence of the chiral conformations but evidence a moderate but definite asymmetric induction from the chiral anion onto the cations. Finally, DFT calculations offer a valuable insight on the geometries, the corresponding stereodynamics and also on the very large difference in NMR for some of the diastereotopic protons.

How to Manipulate Through-Space Conjugation and Clusteroluminescence of Simple AIEgens with Isolated Phenyl Rings.

Apart from the traditional through-bond conjugation (TBC), through-space conjugation (TSC) is gradually proved as another important interaction in photophysical processes, especially for the recent observation of clusteroluminescence from nonconjugated molecules. However, unlike TBC in conjugated chromophores, it is still challenging to manipulate TSC and clusteroluminescence. Herein, simple and nonconjugated triphenylmethane (TPM) and its derivatives with electron-donating and electron-withdrawing groups were synthesized, and their photophysical properties were systematically studied. TPM was characterized with visible clusteroluminescence due to the intramolecular TSC. Experimental and theoretical results showed that the introduction of electron-donating groups into TPM could red-shift the wavelength and increase the efficiency of clusteroluminescence simultaneously, due to the increased electronic density and stabilization of TSC. However, TPM derivatives with electron-withdrawing groups showed inefficient or even quenched clusteroluminescence caused by the vigorous excited-state intramolecular motion and intermolecular photoinduced electron transfer process. This work provides a reliable strategy to manipulate TSC and clusteroluminescence.

Exploring mechanisms of different active species formation in heterogeneous Fenton systems by regulating iron chemical environment

How chemical environment of iron influence active species formation in heterogeneous Fenton processes is poorly understood. Herein, a series of metal organic frameworks (MOFs) with various substituents (UiO-66-X) were prepared as templates for iron chemical environment regulation. The results show that bisphenol A (BPA) degraded in the system modified with electron-donating groups (X = NH2, OH, OCH3) was predominantly attributed to HO. While Fe(IV) was detected in systems modified with electron-withdrawing groups (X = Cl, F, NO2). The introduction of electron-donating groups on FeOx@UiO-66-X increases the length of Fe-O bond from 2.06 to 2.12 Å, and reduces the binding energy of H2O2 on FeOx, which were beneficial for HO generation. However, electron-withdrawing groups (X = Cl, F, NO2) reduces the Fe-O bond length to 1.99 Å, and generates transition product Fe(IV)O. Consequently, this research contributes to the first mechanistic insight into active species regulation during Fenton-like processes by manipulating substituents on MOFs ligand.

The effects of electron-withdrawing and electron-donating groups on the photophysical properties and ESIPT of salicylideneaniline

The photophysical properties and excited state intramolecular proton transfer (ESIPT) of salicylideneaniline (1a) and its derivatives (1b-1e) with different substituents have been investigated using the DFT and TD-DFT methods. The calculated results indicate that the introduction of electron-withdrawing group CN weakens the intramolecular hydrogen bond (H···N). However, the introduction of electron-donating group N(CH3)2 strengthens it. When the CN and N(CH3)2 groups are introduced simultaneously, the intramolecular hydrogen bond (H···N) is weakened. In addition, swapping the CN and N(CH3)2 group positions can enhance the intramolecular hydrogen bond (H···N). Compared to 1a, the absorption and emission spectra of compounds 1b-1e are red-shifted. Frontier molecular orbital analyses prove that the more intense intramolecular charge transfer characters caused by CN and N(CH3)2 substituents is responsible for the red shift of spectra. Potential energy curves indicate that ESIPT in salicylideneaniline (1a) and the CN substituted derivative (1b) is a non-barrier process, while in the N(CH3)2 substituted derivative (1c) and the CN and N(CH3)2 co-substituted derivative (1d), ESIPT needs to overcome the energy barriers of 2.32kcal/mol and 3.38kcal/mol, respectively. Exchanging the positions of CN and N(CH3)2 groups (1e) makes the ESIPT into a barrier-free process. Therefore, the substitution and position of CN and N(CH3)2 groups can affect the ESIPT process and induce different photophysical properties.

New quinacridone derivatives: Synthesis, photophysical and third-order nonlinear optical properties

A series of quinacridone third-order nonlinear optical chromophores containing phenyl, 4-methoxyphenyl and N,N-bis(4-methoxyphenyl)aniline groups were designed and synthesized. The optical properties, electrical properties, theoretical calculations and Z-Scan of the compounds were measured and analyzed to investigate the relationship between structure and third-order NLO properties. The experimental results showed that the introduction of electron-donating groups at the N-position of quinacridone decreases the energy gap (Egap) between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecule, and promotes intramolecular charge transfer (ICT). Quinacridone derivatives containing N, N-bis (4-methoxyphenyl) aniline have good third-order nonlinear optical properties, with the nonlinear absorption coefficient (β) value of 1.4319 × 10−13 and the second-order superpolarizability (γ) of 2.6849 × 10−33 esu.

An exploration of new avenues regarding deep tissue penetration and highersinglet oxygen efficiencies: novel near-IR photosensitizers for photodynamictherapy

A series of novel BODIPY-bearing electron-withdrawing groups at the meso position are reported here. According to the optical measurements, it may be clearly seen that the introduction of electron-donating groups into 3,5-positions and the presence of electron-withdrawing groups at the meso position of the BODIPY core resulted in spectacular bathochromic shifts (up to ∼ 304 nm), and the projected photosensitizers had absorption bands in the therapeutic window of the electromagnetic spectrum (600-900 nm). The absorption maxima of compounds 4,5,6, and 7 were at 886 nm, 890 nm, 760 nm, and 761 nm, respectively. The singlet oxygen generation experiments revealed that compounds 6 and 7, with high singlet oxygen quantum yields (0.52 and 0.93, respectively), were excellent and promising candidates for photodynamic therapy. The singlet oxygen quantum yield of 0.93 was the highest reported value so far for BODIPY-based photosensitizers.

Progress of polymer chain structure regulation of alkaline anion-exchange membranes for fuel cells

Alkaline anion-exchange membrane fuel cells (AAEMFCs) have attracted worldwide interest due to their advantages including fast oxygen reduction kinetics, high compatibility with non-precious-metal catalyst and low cost. As one of the key components in AAEMFCs, the performance of alkaline anion exchange membranes (AAEMs) directly affects the power output and durability of the fuel cells. During fuel cell operating, AAEMs require high ionic conductivity, excellent dimensional and chemical stability to ensure high efficiency and outstanding durability. However, it is still difficult for any type of the AAEMs to meet all these requirements. This monograph summarizes recent development around the world for AAEMs, especially for the trade-off effect between ionic conductivity and stability of AAEMs as well as the proposed strategies for this issue. The charge carrier in AAEMs is OH-, and it has a lower transporting efficiency owing to its lower mobility, higher dependence on water molecular and the blocking of many hydrophobic domains in AAEMs. The improvement of ion-exchange capacity (IEC) by increasing the grafting degree (GD) of cationic functional groups can, to some extent, solve this issue. however, a high GD always bring the following negative issues: (1) Excessive swelling of AAEMs and significant reducing in the dimensional stability of membranes; (2) the increase of OH- concentration accelerates the kinetics of nucleophilic substitution and Hofmann elimination, leading to the degradation of cationic groups; (3) the enhanced polarization of the cationic groups and the hydrophilicity of the main chain enable the polymer backbone susceptible to nucleophilic attack by OH-, resulting in the degradation of the membrane, and even short-circuit of the fuel cells. In order to solve these issues, various of polymer chain architectures have been designed and regulated. To balance the ionic conductivity and the dimensional stability in AAEMs, double, triple and multi-cations are grafted on one site of polymer backbone to achieve a sufficiently high IEC at relatively low GD. Another realistic strategy is constructing 3D anion channels by the segregated hydrophilic/hydrophobic phase. The alkali stability of the cationic groups is affected by many factors including field effects, steric effects and conformation of substituent groups, and so on. The improvement of chemical stability of AAEMs has been another formidable scientific challenge. Researchers reduce the kinetics of the nucleophilic substitution and elimination reactions, and improve the basic stability of the cationic groups by modulating the structure of substituent groups such as the introduction of electron-donating groups, increased steric hindrance, and adequate hydration of OH-. Among various cationic groups, the piperidinium-based cations show high resistance against both nucleophilic substitution and elimination in alkaline conditions and at elevated temperature. Furthermore, the polymer backbones without ether band and electron-withdrawing groups have been synthesized and exabit highly resistant to alkali hydrolysis. Recently, new strategy for constructing ordered ion channels in AAEMs by novel porous materials such as metal-organic frameworks (MOF), Trogers base, and macrocyclic crown ether compounds, provide for efficient ionic transport. Additionally, highly stable metal complexes have been used as cationic group in AAEMs. These new trends will open up an exciting opportunity to design high-performance AAEMs. The appearance of highly stable AAEMs enables the AAEMFCs to be operated at 80°C, and the cell works stably in a period of study over 100 h. Although this progress is encouraging, there still remains work for improving the cell performance and stability. A 1000 h of stable operation at elevated temperatures will be the next mission for AAEMFCs. In addition, there are some fundamental issues necessary to explore, such as the transport mechanism of OH- in the membrane, the molecular interaction of polyelectrolytes and their self-assembly mechanism in solution and film formation, the mechanism of the influence of morphology on the chemical stability of AAEMs, and the factors affecting the long-term stability of AAEMFCs. These scientific issues will be the focus of future research. The development of AAEMFCs is on its way, and it calls for more efforts in fundamental study, polymer chain architectures and morphology designing, and fuel cell engineering to make it viable.

Exploration on Charge Transfer and Absorption Spectra of Spiro[fluorene-9,90-xanthene]-based Polyoxometalate Hybrids Toward High Performance Dye-sensitized Solar Cell

Based on spiro[fluorene-9,90-xanthene](SFX, dye 1), the Lindqvist-type polyoxometalate(POM) functio-nalized with SFX and its derivatives(dyes 2―4) used in dye-sensitized solar cells(DSSCs) were designed and inves-tigated with the density functional theory(DFT) and time-dependent DFT(TD-DFT) calculations. The results indicate that Lindqvist-type POM is the main contribution to the lowest unoccupied molecular orbital(LUMO) and affects the LUMO energies of dyes 2―4. The maximum absorptions of the designed dyes containing POM(dyes 2―4) are red shifted comparing with that of dye 1. The introduction of electron-donating group onto SFX segment is helpful to red shift the absorption spectra. The major factors affecting the performance of DSSCs, including light harvesting and electron injection were evaluated. Considering the absorption spectra and photovoltaic parameters, dyes 3 and 4 are promising high performance dye sensitizers in n-type DSSCs.

Spiropyrans and spirooxazines 13. Synthesis and photochromic properties of benzoxazolyl-substituted spirobenzopyrans

New benzoxazolyl-substituted spiroindoline-benzopyrans with electron-withdrawing groups in the indoline fragment were obtained. These compounds exhibit positive P- and T-type photochromism. Structural correlations of the spectrokinetic properties depending on the variation of substituents in the indoline part of the spiropyran molecules were established. Electronwithdrawing groups were found to cause a bathochromic shift of the long-wavelength absorption maxima of the merocyanine isomers as compared to the unsubstituted spiropyran and decrease their lifetime. Conversely, an introduction of electron-donating groups results in a hypso chromic shift of the absorption maxima and an increase in the lifetime of the colored isomers of spiropyrans. Electron-withdrawing substituents at the position 5 of the indoline fragment cause the increase of the colorability of the spiropyrans.

Sodium perborate/NaNO2/KHSO4-triggered synthesis and kinetics of nitration of aromatic compounds

Sodium perborate (SPB) was used as efficient green catalyst for NaNO2/KHSO4-mediated nitration of aromatic compounds in aqueous acetonitrile medium. Synthesis of nitroaromatic compounds was achieved under both conventional and solvent-free microwave conditions. Reaction times were comparatively shorter in the microwave-assisted than conventional reaction. The reaction kinetics for nitration of phenols in aqueous bisulfate and acetonitrile medium indicated first-order dependence on [Phenol], [NaNO2], and [SPB]. Reaction rates accelerated with introduction of electron-donating groups but retarded with electron-withdrawing groups. Kinetic results did not fit well quantitatively with Hammett’s equation. Observed deviations from linearity were addressed in terms of exalted Hammett’s constants (\( \bar{\sigma } \) or σeff), para resonance interaction energy (ΔΔGp) parameter, and Yukawa–Tsuno parameter (r). This term provides a measure of the extent of resonance stabilization for a reactive structure that builds up charge (positive) in its transition state. The observed negative entropy of activation (−ΔS#) suggests greater solvation and/or cyclic transition state before yielding products.

Near-infrared electron acceptors based on terrylene diimides for organic solar cells

The introduction of electron-donating groups into TDI broadens the absorption spectra and enhances the charge transport and photovoltaic performance.

Potassium Periodate/NaNO2 /KHSO4 -Mediated Nitration of Aromatic Compounds and Kinetic Study of Nitration of Phenols in Aqueous Acetonitrile

Synthesis and kinetics of potassium periodate(KIO4)/NaNO2/KHSO4)-initiated nitration of aromatic compounds have been studied in aqueous acetonitrile medium. Synthesis of nitroaromatic compounds is achieved under conventional and solvent-free microwave conditions. Reaction times in microwave-assisted reaction are comparatively less than in conventional reaction. The reaction kinetics for the nitration of phenols in aqueous bisulfate and acetonitrile medium indicated first-order dependence on [phenol], [NaNO2], and [KIO4]. An increase in [KHSO4] accelerated the rate of nitration under otherwise similar conditions. The rate of nitration increased in the solvent of high dielectric media (solvents with high dielectric constant (D)). Observed results were in accordance with Amis and Kirkwood plots [log k′ vs. (1/D) and [(D − 1)/(2D + 1)]. These observations probably indicate the participation of anionic species and molecular or (dipolar) species in the rate-determining step. In addition, the plots of (log k′) versus volume% of organic solvent were also linear, which probably indicate the importance of both electrostatic and nonelectrostatic forces, solvent–solute interactions during nitration of phenols. Reaction rates accelerated with the introduction of electron-donating groups and retarded with electron-withdrawing groups, but results could not be quantitatively correlated with Hammett's equation and depicted deviations from linearity. These deviations could probably be attributed to cumulative effects arising inductive, resonance, and steric effects. Leffler's plot (ΔH# vs. ΔS#) was found linear indicating the compensation (cumulative) effect of both enthalpy and entropy parameters in controlling the mechanism of nitration.