Electron Donor-acceptor Research Articles

Cucurbit[8]uril-stabilized charge transfer: An efficient supramolecular approach toward a heterogeneous organic photocatalyst for aerobic oxidation reactions.

Host-stabilized charge transfer (HSCT) has been widely utilized in macrocycle-derived supramolecular assemblies and architectures. However, there has been less research attention focused on the direct fabrication of pure organic photocatalysts using HSCT. Herein, four viologen derivatives (m-PV2+, m-BPV2+, d-PV2+, and d-BPV2+) with different electron donor-acceptor (D-A) structures were synthesized. Their host-guest complexes with cucurbit[8]uril (Q[8]) in an aqueous solution could be switched using the substituted electron donor moieties, in which the host-guest complexes of m-BPV2+@Q[8] andd-BPV2+@Q[8] exhibited HSCT interactions. Control experiments revealed that the d-BPV2+@Q[8] complex had the strongest ability to sensitize singlet oxygen (1O2). This was ascribed to the increased π-conjugation of d-BPV2+@Q[8], which led to more effective HSCT upon encapsulation by the Q[8] host. Consequently, the d-BPV2+@Q[8] complex could be easily employed as a heterogeneous photocatalyst for the photooxidation reaction of thioether com-pounds with high selectivity. In particular, d-BPV2+@Q[8] was successfully applied to the synthesis of sulfoxide drugs, such as the con-version of inexpensive Iberverin ($7.0 per gram) to the expensive bioactive inhibitor Iberin ($19500.0 per gram) in high yield (94%).

Photocatalytic C‐I Bond Borylation and Phosphorylation of Diaryliodonium Salts with Excellent Atom‐Economy

Highly atom‐economic conversion of diaryliodonium salts represents an underdeveloped but highly desirable domain. Most reactions involving these species only utilize single aryl group of the diaryliodonium and produce an equivalent of aryl iodide as waste. Herein, by further transforming the side‐product aryl iodide, we report an overall new two‐step one‐pot strategy that allows photocatalytic C−I bond borylation and phosphorylation of diaryliodonium salts and ensures effective conversion of both aryl groups of the diaryliodonium into the relevant arylboronic esters or arylphosphonic esters. Mechanistic investigations suggest that electron‐donor‐acceptor (EDA) complex is formed between the photocatalyst phenothiazine (PTH) and diaryliodonium salt substrate. Upon visible light irradiation, this complex produces aryl radical and aryl iodide. With addition of a base in the second step, the reducing ability of the photocatalyst is enhanced via proton‐coupled electron transfer (PCET) process, thereby aryl iodide produced in the first step is reduced to yield aryl radical again. Both aryl radicals generated in the two steps react with B2(OR)4 or P(OR)3 to produce the corresponding monoarylation product in a quantitative yield.

Organophotocatalytic Reduction of Benzenes to Cyclohexenes.

The reduction of abundant benzene rings to scarce C(sp3)-rich motifs is invaluable for drug design, as C(sp3) content is known to correlate with clinical success. Cyclohexenes are attractive targets, as they can be rapidly elaborated into large product libraries and are stable against rearomatization. However, partial reduction reactions of benzenes to cyclohexenes are rare and have a very narrow scope. Herein we report a broadly applicable method that converts electron-poor benzenes to cyclohexenes and tolerates Lewis-basic functional groups such as triazoles and thioethers as well as reducible groups such as cyanides, alkynes, and sulfones. The reaction utilizes an organic donor that induces mild arene reduction by preassociation to a photoexcitable electron donor-acceptor (EDA) complex and mild isomerization of redox-inert 1,4-cyclohexadienes to reducible 1,3-cyclohexadienes without a strong base in its oxidized thioquinone methide form.

Modelling of (N-vinylcarbazole)/Fullerene nanoheterojunction for organic solar cells and photovoltaics applications – A DFT Approach

The current manuscript depicts the construction of a novel hybrid carbon nanomaterials with fascinating electronic and chemical properties and tunable energy bandgap of a nano heterojunction comprising (9-vinyl carbazole), VK and fullerene, C60. A comprehensive investigation of VK/C60 adsorption surface is conducted using ab-initio density functional theory calculations with van der Waals corrections (GGA+vdW) implemented. The novel nanoheterostructure interfaces synthesized by DFT methods have low-bandgap characteristics (1.112–1.223 eV), broaden absorption wavelengths and photovoltaic characteristics. This novel VK/C60 nanoheterostructure composites have finite bandgaps and good stability and, therefore, have promising applications for photovoltaic devices. Optoelectronic features of all three developed systems are recommended for future solar cell applications. The studies reveal that the VK/C60 nanoheterojunctions can behave as efficient electron donor-acceptor components in organic solar cells (OSCs) that make them potential candidates for the development of low-cost optoelectronic devices. The band gap values calculated in this work are low enough to make the nanoheterostructures exceedingly promising for photovoltaic applications.

A new Conjugated mesoporous polymer as fluorescence sensor for the detection of nerve agent simulant dimethyl chlorophosphonate via specific nucleophilic substitution reaction

Conjugated micro/mesoporous polymers (CMPs) represent a category of porous organic materials formed via covalent bonds. Here, DAC-TFP CMP was synthesized using 3,6-diaminocarbazole (DAC) and 2-hydroxy-1,3,5-benzenetricarbaldehyde (TFP) as building blocks. DAC-TFP CMP is a porous conjugation polymer with remarkable thermal and chemical stability. DAC-TFP CMP suspension demonstrates selective "on-off" fluorescence response towards nerve agent simulant dimethyl chlorophosphonate (DMCP) in 1,4-dioxane with exceptionally low detection limits. DMCP and DAC-TFP CMP undergo a nucleophilic substitution reaction, leading to the formation of an N-P bond between N atom on carbazole of DAC-TFP CMP and P atom of DMCP. The new polymer DAC-TFP CMP@DMCP has electron donor-acceptor structure and the fluorescence quenching can be ascribed to the intramolecular charge transfer (ICT) from DAC-TFP CMP unit to DMCP group, as supported by XPS results and DFT calculation. Upon the addition of DMCP to the 1,4-dioxane suspension of DAC-TFP CMP, a subtle blue shift is observed in both the fluorescence emission spectra and UV-vis absorption spectra, providing further validation of the ICT mechanism. DAC-TFP CMP shows excellent recoveries in detecting DMCP in both soil and pesticide samples containing mesotrione and atrazine, highlighting its strong potential as a reliable chemosensor for DMCP detection and analysis.

The Photophysics of Naphthalimide-Phenoselenazine Electron Donor-Acceptor Dyads: Revisiting the Heavy-Atom Effect in Thermally Activated Delayed Fluorescence.

We prepared thermally activated delayed fluorescence (TADF) emitter dyads, NI-PTZ, NI-PTZ-2Br and NI-PSeZ, with naphthalimide (NI) as electron acceptor and 10H-phenothiazine (PTZ) or 10H-phenoselenazine (PSeZ) as electron donor to study the heavy-atom effect on the intersystem crossing (ISC) and reverse ISC (rISC) in the TADF emitters. The delayed fluorescence lifetimes of the dyads containing heavy atoms ( =5.9 μs for NI-PSeZ and =16.5 μs for NI-PTZ-2Br, respectively) are longer than the heavy atom-free counterpart NI-PTZ ( =2.0 μs). Nanosecond transient absorption (ns-TA) spectral study and the time-resolved electron paramagnetic resonance (TREPR) spectra show the presence of both 3LE and 3CS states. These findings represent solid experimental evidences for the spin-vibronic coupling mechanism of TADF. Moreover, the ns-TA spectra show that the heavy atoms don't have a significant effect since the lifetime of the triplet transient species (1.3 μs for NI-PTZ) is not shortened in their presence (4.5 μs for NI-PSeZ and 5.3 μs for NI-PTZ-2Br). These results show that the previously claimed heavy-atom effect on rISC and TADF is not a universal principle. The femtosecond transient absorption (fs-TA) spectra of the compounds indicate the occurrence of fast charge separation within 1-2 ps, and the charge recombination is slow (>4 ns).

Visible-Light-Induced Divergent Oxygenation of Methylbenzene Utilizing Aryl Halides.

The selective oxidation of methylbenzene to value-added products is of indisputable importance in organic synthesis. Although photocatalytic oxidation reactions of toluene have achieved great success for the preparation of its oxidative products, such as carboxylic acids, benzaldehyde, and benzoate, there remains a lack of a unified photocatalytic system for the selective preparation of these oxidation products. Herein, we report a metal- and additive-free photocatalytic protocol enabled by aryl halides using O2 as a green oxidant for the selective synthesis of the above-mentioned three oxidation products by adjusting the reaction solvent. This strategy features many advantages, including environmentally friendly and mild reaction conditions, broad substrate applicability and functional group tolerance, and potential practical application for the synthesis of aromatic carboxylic drugs and polymer materials and degradation of polystyrene waste. The continuous-flow system was utilized for the oxidation of toluene, which resulted in a reduced reaction time and increased production efficiency. Detailed mechanistic investigation revealed that the hydrogen atom transfer process was facilitated by the bromine radical from aryl halides for further oxidation, and an electron donor-acceptor complex of methylbenzene and aryl halides may exist.

Exploring optical, electronic and NLO properties: Growth and characterization of rubidium hydrogen (+)- tartrate crystals

Rubidium, a highly reactive alkali metal, is used in several research areas, such as electronics for its light-emitting properties, and in making glass, ceramics, and in biomedical studies. Single crystals of Rubidium Hydrogen (+)-Tartrate (RHT) suitable for the X-ray analysis were obtained from water solution. The crystal structure of the RHT crystal was determined using single crystal XRD, revealing an orthorhombic system with a non-centrosymmetric space group, P212121. The lattice parameters were a = 7.9233 Å, b = 10.9883 Å, and c = 7.6527 Å, with a unit cell volume of 666.272 ų. The structural vibrations of the RHT compound were analysed using FT-IR and FT-Raman spectroscopy, while NMR provided further insights into its molecular structure. Theoretical investigations at the DFT/RB3LYP/LANL2DZ level were conducted to explore the molecular structure, vibrational spectra, and bonding interactions within the RHT compound's molecular system. Natural Bond Orbital (NBO) analysis of the RHT compound revealed significant charge transfer interactions and stabilization energies, particularly highlighting strong electron donor-acceptor correlations that contribute to the molecule's overall stability. The UV–Vis and HOMO-LUMO calculations were performed in the gas phase. Optical conductivity studies have been performed. The broad spectral curve in the photoluminescence spectrum reflects the optical effects and showed a significant intense peak at 281.22 nm and a moderately intense peak at 395.9 nm. First order hyperpolarizability studies reveals that nonlinear optical efficiency is 1.06 times better than urea and 58.19 times than KDP. Furthermore, Third Harmonic Generation (THG) studies using the Z-scan technique were also conducted to investigate the nonlinear properties.

Harnessing the potential of coal-derived graphene oxide/epoxy nanocomposites: Enhancing thermal conductivity and fracture toughness

The choice of precursor material significantly influences the properties of graphene oxide (GO), thereby providing its adaptability across diverse applications. Coal, with its distinctive molecular structure characterized by graphene-like domains and aliphatic side chains, as well as abundant impurities and heteroatoms featuring specific functional groups, emerges as a promising precursor. Employing a recently developed facile one-pot process for synthesizing semianthracite coal-derived GO (AC-GO), we have, in this study, explored its potential as a nanofiller in an epoxy matrix, resulting in AC-GO-enriched nanocomposites. The main purpose of the project was to introduce AC-GO within the epoxy matrix to enhance its thermal conductivity and fracture resistance by enhancing interfacial interactions. Our findings indicate remarkable enhancements in thermal conductivity (0.646 Wm-1K-1 at 1.0 wt% loading) and fracture toughness (6.7 MPam1/2 at 0.8 wt% loading) within AC-GO loaded nanocomposites, with these improvements being 255 % and 215 %, respectively, over those for the epoxy matrix. Remarkably, they surpass those achieved with graphite-derived GO (Gr-GO) by approximately 112 % and 76 %, respectively. Enhancing thermal conductivity and fracture toughness in epoxy nanocomposites is vital for effective heat dissipation and durability, making them ideal for high-performance electronics, aerospace, and automotive applications. These improvements can be attributed to the enhanced interactions between oxygen moieties located at the periphery of AC-GO and the fundamental epoxy-amine hardener system within the resin formulation, fostering electron acceptor–donor interactions. Furthermore, we introduce a new figure of merit (FOM) that accurately captures the combined role of thermal conductivity and fracture toughness. It is shown that this FOM can serve as a useful design tool for selecting an optimal nanofiller loading for targeted applications. The findings of our paper highlight the versatility and unique attributes of AC-GO, offering promising opportunities for applications in the industrial engineering, owing to their outstanding interfacial properties.

Electron Donor-Acceptor Complex-Driven Divergent Routes to α-Amino Bicyclopentyl Iodides and Methylene Cyclobutanols.

Amines are essential due to their structural diversity and biological significance. Introducing the valuable bicyclopentane (BCP) moiety at the α-position of amines offers a promising strategy for developing novel bioactive compounds. This study outlines a divergent synthesis approach to generate α-amino-functionalized bicyclopentyl iodides and methylene cyclobutanols under mild and environmentally sustainable conditions. By employing an electron donor-acceptor (EDA) complex between amine and the inexpensive and readily available inorganic base Cs2CO3, this method circumvents the need for strongly reducing, metal-based photocatalysts typically required for aryl radical generation. This approach enables the α-functionalization of various aliphatic and alicyclic amines via a 1,5-hydrogen atom transfer mechanism.

Photoredox-Catalyzed C-H Methylation of N-Heteroarenes Enabled by N,N-Dimethylethanolamine.

A visible-light-driven radical C-H methylation of N-heteroarenes that is efficient and additive- and catalyst-free and employs readily available N,N-dimethylethanolamine as the methyl source has been developed. The transformation offers the benefits of broad substrate scope, mild reaction conditions, and operational simplicity. A photoactive electron donor-acceptor (EDA) complex between N-heteroarenes and N,N-dimethylethanolamine is essential for this transformation, as revealed by mechanistic investigations.

Intersystem Crossing, Photo-Induced Charge Separation and Regioisomer-Specific Excited State Dynamics in Fully Rigid Spiro Rhodammine-Naphthalene/Anthraquinone Electron Donor-Acceptor Dyads.

We prepared a series fully rigid spiro electron donor-acceptor orthogonal dyads, with closed form of rhodamine (Rho) as electron donor and naphthalene (Np)/anthraquinone (AQ) as electron acceptor, to access the long-lived triplet charge separation (3CS) state, via the electron spin control method. We found strong dependency of the photophysical property of the dyads on the amino substitution positions of the Np chromophores in the dyads 1,8-DaNp-Rho and 2,3-DaNp-Rho. Nanosecond transient absorption (ns-TA) spectra show the population of the 3LE state (lifetime: 47 μs) for 2,3-DaNp-Rho, however, long-lived 3CS state was observed (τCS = 0.62 μs) for AQ-Rho, with a CS quantum yield of ΦCS = 58%. Based on femtosecond transient absorption (fs-TA) spectra, spin orbit charge transfer ISC (SOCT-ISC) is proposed to be responsible for the formation of the triplet states. Time-resolved electron paramagnetic resonance (TREPR) spectra of AQ-Rho indicate the presence of two states, a 3LE state with zero field splitting (ZFS) D parameter of 1400 MHz and E parameter of -410 MHz, formed via radical pair ISC (RP-ISC) and SOCT-ISC mechanism; and a 3CS state with the electron spin-spin interaction in the regime of spin-correlated radical pair (SCRP).

Visible light induced reactions of quinones

AbstractThis review covers the visible light induced reactions of quinones such as benzoquinone, naphthoquinone, and anthraquinone. These quinones are distinguished by their fully conjugated structures, which feature minimal energy gaps, and nonbonding electron pairs on the oxygen atoms. Such structural attributes facilitate np → π* transition, allowing for easy access to excited states and rendering quinones highly reactive under visible‐light irradiation. We describe three primary types of reactions facilitated by these electronic characteristics: Paternò–Büchi (PB) reactions, which entail [2 + 2] photocycloaddition between the carbonyl groups of quinones and alkenes or alkynes; CH activation processes, which showcase quinones' versatility in functionalizing hydrocarbons; and the formation of electron donor–acceptor complexes, demonstrating quinones' capability to engage in charge transfer interactions. Through this review, we highlight the critical role quinones play in photochemistry, their unique electronic properties, and their broad applicability in synthetic organic chemistry.

Visible-light-induced hydrosulfonylation of alkynes driven by electron-donor–acceptor (EDA) complexes

The method toward the vinyl sulfones has been realized by visible-light-induced hydrosulfonylation of alkynes via an EDA process. DIPEA was used as both electron donor for EDA complex and hydrogen donor for hydrogen atom transfer.

Precise Single-Atom Modification of Hybrid Lead Chlorides for Electron Donor-Acceptor Effect and Enhanced Photocatalytic Aerobic Oxidation.

Hybrid lead halides show significant potential in photocatalysis due to their excellent photophysical properties, but the atomically precise modification of their organic component to achieve synergistic interactions with the lead halide units remains a great challenge. Herein, for the first time, we have employed the crystal engineering strategy to construct a class of single-atom-substituted hybrid lead halides with electron donor-acceptor (D-A) effect. The lead halide frameworks consist of 1D linear [PbCl]+ chains as inorganic building units and benzoxadiazole/benzothiadiazole/ benzoselenadiazole-funtionalized dicarboxylates as linkers. The covalent bonding between the organic ligands with electron-withdrawing groups and the electron-rich lead halide units not only facilitate the charge separation, but also enhance structural robustness that is critical for photocatalysis. The D-A structured lead halides serve as highly efficient heterogeneous photooxidation catalysts, including aerobic oxidation of C(sp3)-H bonds, oxidative coupling of primary amines, oxidation of phenylboronic acids and selective oxidation of sulfides that are demonstrated in 30 examples. Importantly, these photooxidation reactions are able to be driven by natural sunlight and ambient air to afford quantitative yields. Moreover, our lead halide photocatalysts are successful to fix into a photocatalytic flow system, which enables the flow-type synthesis of high value-added photooxidation products on a gram scale.

Photoactivated Formal [3 + 2]/[4+2] Cycloaddition of N‐Aryl Cyclopropyl and Cyclobutylamines

AbstractOrganic transformations initiated by photochemical activation have been at the forefront of reaction discovery. In this study, we present a formal photochemical [3+2] and [4+2] cycloaddition using N‐aryl cyclopropylamines and N‐aryl cyclobutylamines in conjunction with α,β‐unsaturated carbonyl systems, unveiling two distinct mechanistic pathways. The [3+2] cycloaddition is elucidated as being guided by the photochemical activity of an electron donor‐acceptor (EDA) complex. Simultaneously, intermolecular [4+2] annulation of cyclobutylanilines is achieved by visible‐light photoredox catalysis. These simple methodologies have wide applicability, facilitating the synthesis of N‐arylaminocycloalkyl compounds in yields ranging from good to excellent.

C(sp2)-Arylsulfones Directly from Arylsulfonyl Chlorides with Boronic Acids by Photoactivation of Boosted EDA Complexes.

Directly with arylsulfonyl chlorides, a green and efficient deborylativesulfonylation of aryl(alkenyl)boronic acids has been developed to access both diarylsulfones and vinylarylsulfones in moderate to excellent yields at room temperature under visible-light irradiation. This protocol features broad C(sp2)-arylsulfone applicability, simple operation, accessibility of raw materials and ease of scale-up. The key to the success of this photoredox transformation is introducing catalytic amounts of additives, naphthalen-2-ols, thus boosting the formed electron donor-acceptor (EDA) complexes, which can dramatically improve not only the reaction efficiency but also the selectivity. This strategywas inspired and derived from specific substrates, representing a rare paradigm of how to exploit a more general reaction system. Moreover, extensive control experiments provide insights into the proposed mechanism.

Electron-Donor-Mediated Divergent Transformation of Br-RF via EDA Complex for the Synthesis of Fluorine-Containing Oxindoles and Amides.

We have developed an unprecedented electron-donor-controlled divergent reaction between N-alkylsulfonylated acrylamides and Br-RF, facilitated by an electron donor-acceptor (EDA) complex, for the synthesis of fluorine-containing oxindoles and amides. Key to this divergent transformation is the EDA complex generation by altering electron donors. This approach has several advantages, such as broad substrate scope, being metal-catalyst- and photocatalyst-free, and having good functional group tolerance.

Visible light-promoted, catalyst-free synthesis of isoniazid azomethines: In vitro antioxidant activity, molecular docking, ADME and toxicity prediction

Green synthesis of biologically active molecules is essential for environmental sustainability, resource efficiency, reduced environmental impact, and compliance with regulations. It ensures a safer working environment, and fosters innovation in sustainable chemistry practices. In this context, we introduce an electron donor-acceptor (EDA)-mediated visible light-promoted, catalyst-free (VLCF) scalable synthesis of isoniazid azomethines. This synthesis encompasses the drug salizide and its analogues, which were subsequently evaluated for their antioxidant activities. Isoniazid azomethines 3e demonstrated superior activity compared to salizide and ascorbic acid, with an IC50 of 0.078 mg/mL in the hydrogen peroxide antioxidant assay. Specifically, 3e exhibited greater antioxidant properties (79.02 %) than isoniazid azomethine 3b (75.82 %), isoniazid azomethine 3d (62.2 %), isoniazid azomethine 3c (59.86 %), and isoniazid azomethine 3a (54.62 %). In the superoxide dismutase antioxidant assay, 3e was also identified as the most active, with a SOD activity level of 650 U/mg of protein, surpassing other compounds (3a-d) with SOD activity levels of 330, 560, 350, and 420 U/mg of protein, respectively. Molecular docking against horseradish peroxidase (1W4Y) showed compound 3e with the best binding energy (-6.561 kcal/mol), forming key hydrogen bonds (Asn135, Pro139) and a π-cation interaction with Arg38. These interactions suggest 3e may effectively inhibit hydrogen peroxide catalysis. The in silico assessment of the physicochemical properties, pharmacokinetics, and toxicology of synthesized compounds suggests that these compounds exhibit promising ADMET characteristics, with no identified toxicological concerns.

Solvent Dictated Organic Transformations.

Solvent plays an important role in many chemical reactions. The C-H activation has been one of the most powerful tools in organic synthesis. These reactions are often assisted by solvents which not only provide a medium for the chemical reactions but also facilitate reaching to the product stage. The solvent helps the reaction profile both chemically and energetically to reach the targeted product. Organic transformations via C-H activation from the solvent assistance perspective has been discussed in this review. Various solvents such as tetrahydrofuran (THF), MeCN, dichloromethane (DCM), dimethoxyethane (DME), 1,2-dichloroethane (1,2-DCE), dimethylformamide (DMF), dimethylsulfoxide (DMSO), isopropyl nitrile (iPrCN), 1,4-dioxane, AcOH, trifluoroacetic acid (TFA), Ac2O, PhCF3, chloroform (CHCl3), H2O, N-methylpyrrolidone (NMP), acetone, methyl tert-butyl ether (MTBE), toluene, p-xylene, alcohols, MeOH, 1,1,1-trifluoroethanol (TFE), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), tert-amyl alcohol and their roles are discussed. The exclusive role of the solvent in various transformations has been deliberated by highlighting the substrate scope, along with the proposed mechanisms. For easy classification, the review has been divided into three parts: (i) solvent-switched divergent C-H activation; (ii) C-H bond activation with solvent as the coupling reagent, and (iii) C-H activation with solvent caging and solvent-assisted electron donor acceptor (EDA) complex formation and autocatalysis.