Electron Donor-acceptor Research Articles

DFT study of electron donor-acceptor (EDA) complexes: mechanism exploration and theoretical prediction.

Organic synthesis methods initiated by visible light have received increasing attention from synthetic chemists. Reactions initiated by EDA complexes do not require the use of toxic or expensive photoredox catalysts, unlike traditional photoreaction processes. However, this kind of reaction requires a particular structure for the substrate, so it is important to study the detailed and systematic reaction mechanism for its design. EDA complexes of substituted 1H-indole and substituted benzyl bromide derivatives were studied by density functional theory (DFT). The difference between EDA complexes with substituents of different kinds and locations were compared by theoretical study and a new EDA complex was predicted.

Photo-induced C(sp2)-H difluoroalkylation of anilines.

A photoinduced protocol for the direct difluoroalkylation of C(sp2)-H bonds in anilines under catalyst-free reaction conditions is presented. This transformation is characterized by a wide substrate scope, mild reaction conditions, and operational simplicity, and could serve as an alternative tool to established methods for the synthesis of difluoroalkylated anilines. Mechanistic studies suggest the formation of an electron-donor-acceptor (EDA) complex between anilines and difluoroalkyl bromides in this reaction.

Buckminsterfullerene fragments used as hydrogen carrier: Case of corannulene derivatives

Buckminsterfullerene fragments are interesting to use in hydrogen adsorption because of the suitable properties possessed by their concave structure. In the present paper, adsorption of hydrogen on the bowl-shaped corannulene and its derivatives is investigated. Both electron donor and electron acceptor are explored in the substitution and 28 derivatives are generated. DFT calculations are performed by means of WB97XD functional. The substitution number and the substitution nature of corannulene derivatives are analyzed through results based on several parameters. Besides bowl depth and equilibrium distance, also charge distribution and some reactivity indices, based on MEDT, are reported. Results show that a newly created charge distribution contributes to a better binding process.

Синтез новых S-производных 4-амино-1,3,5-триазин-2-тиона и их исследование методами ЯМР 1Н, 13С и хромато-масс-спектрометрии

4-Amino-1,3,5-triazine-2-thione 1 interacts with allyl bromide, 2-methyl-3-chloro-1-propene, 2,3-dibromopropene-1, prenyl bromide in DMFA/K2CO3 and with cinnamyl chloride, butenyl bromide in DMFA/NaOH to form 4-allylsulfanyl- 2, 4-(2-methylpropene-2-yl)sulfanyl- 3, 4-(2-bromopropene-2-yl)sulfanyl- 4, 4-(2-methylbutene-2-yl)sulfanyl- 5, 4-cinnamylsulfanyl- 6 and 4-(butene-1-yl)sulfanyl-1,3,5-triazine-2-amines 7, respectively. The structure of compounds 2–7 was studied by 1H NMR, as well as of compounds 5 and 7, in their case including 13C NMR; allyl sulfide 2, prenyl sulfide 5 and butenyl sulfide 7 were also studied using chromatography mass spectrometry. In the 1H NMR spectra of compounds 2–7, the weakest field signal in the range of 8.22–8.30 p.p.m. is the signal of the aromatic proton of the triazine cycle, manifested as a singlet. The signals of protons of the S-CH2 group are observed in a strong field – at 3.10–4.19 p.p.m. – depending on the presence of electron donor or electron acceptor groups in the alkenyl fragment. The protons of the =CH2 group are present only in the structure of sulfides 2–4 and 7; they form two signals in the 1H NMR spectra: one signal at 4.85–5.58 p.p.m., the second at 5.03–6.10 p.p.m. In the 13C NMR spectra of prenyl sulfide 5 and butenyl sulfide 7, the carbon atoms of the S-alkenyl groups resonate in the region of strong fields. In the region of weak fields, the signals of aromatic carbon atoms of the 1,3,5-triazine cycle are observed: 182.32–157.95 p.p.m. In the mass spectra of compounds 2, 5 and 7, the characteristic peaks are [M 15]+ and [M-33]+ peaks, the formation of which is associated with the fragmentation of molecular ions undergoing cleavage of the methyl radical and the •SH radical, respectively. The haloalkyl derivative of the heterocyclic series – 2-chloro-1-(2,2,4-trimethyl-4-phenyl-3,4-dihydroquinoline-1(2H)-yl) ethanoate – in reaction with compound 1 has led to the introduction of a new pharmacophore fragment into the simm-triazine molecule, which contributes to the expansion of the spectrum of potential biological activity of its derivatives.

Visible light-driven α-sulfonylation of ketone-derived silyl enol ethers via an electron donor–acceptor complex

We herein describe a versatile electron donor–acceptor complex (EDA) mediated α-sulfonylation of ketone-derived silyl enol ethers using thiosulfonates (acceptor) with DABCO (donor) under visible light irradiation.

Photo-driven reduction/cyclization of nitroarenes via electron donor–acceptor complexes: a novel method for the acquisition of N-heterocycles

An EDA complex-based method for the reduction/cyclization of nitroarenes to obtain N-heterocycles with H2O as a clean by-product is presented.

Light-fuelled nitro-reduction via cascaded electron donor–acceptor complexes in aqueous media

Developed herein is a metal-free method for nitro reduction via cascade electron donor acceptor complex photoexcitation in aqueous media.

Engineering an annular donor–acceptor reaction chamber with spontaneous feedstock collection for boosting CO2 photoreduction

The interaction between methyl and phosphorus atoms constructs a porous reaction chamber and an annular electron donor–acceptor structure in g-C3N4, inducing a spontaneous collection mechanism of feedstock to enhance photoreduction of CO2 to CO.

Electron donor–acceptor complex photoactivation for deaminative alkynylation, alkenylation and allenylation: a comprehensive study

Herein, we disclose our study toward photoinduced deaminative alkynylation, alkenylation and allenylation.

Catalyst-free C–H methylation of heteroarenes enabled by electron donor–acceptor complex photoactivation

A visible-light-induced direct C–H methylation of heterocycles (including quinoxalinones, pyrazinones, quinolinones and coumarins) with methylamines via EDA complex photoactivation was developed.

Mechanism study of the photothermal function of lignin: the effect of electron-withdrawing groups

The photothermal effect of lignin was significantly enhanced by introducing electron-withdrawing group attributing to the improved light absorption by electron donor-acceptor structure and the enhanced non-radiative decay through molecular motion.

Real-time capture of nuclear motions influencing photoinduced electron transfer.

Although vibronic coupling phenomena have been recognized in the excite state dynamics of transition metal complexes, its impact on photoinduced electron transfer (PET) remains largely unexplored. This study investigates coherent wavepacket (CWP) dynamics during PET processes in a covalently linked electron donor-acceptor complex featuring a cyclometalated Pt(ii) dimer as the donor and naphthalene diimide (NDI) as the acceptors. Upon photoexciting the Pt(ii) dimer electron donor, ultrafast broadband transient absorption spectroscopy revealed direct modulation of NDI radical anion formation through certain CWP motions and correlated temporal evolutions of the amplitudes for these CWPs with the NDI radical anion formation. These results provide clear evidence that the CWP motions are the vibronic coherences coupled to the PET reaction coordinates. Normal mode analysis identified that the CWP motions originate from vibrational modes associated with the dihedral angles and bond lengths between the planes of the cyclometalating ligand and the NDI, the key modes altering their π-interaction, consequently influencing PET dynamics. The findings highlight the pivotal role of vibrations in shaping the favorable trajectories for the efficient PET processes.

An electron-donor–acceptor complex between two intermediates enables a N–N bond cleavage cascade process to access 2,3-difunctionalized pyridines

A visible-light-enabled catalyst-free [3 + 2] cycloaddition/N–N bond cleavage/intramolecular C–N bond formation cascade process to access 2,3-difunctionalized pyridines was developed.

Adsorption mechanisms and optimal production of magnetic biochar composites from red mud and soft wood biomass

We investigated the adsorption capacity of four composites generated by co-pyrolyzing red mud, an iron rich waste product from the production of alumina, together with Canadian soft wood biomasses, including Douglas fir, pine wood, red cedar and hemlock. Pyrolysis conditions included manually mixing of both biomass and red mud together before pyrolyzing at 800 °C for 3 h, with a ramp rate of 10 °C/min and a flow rate of 2 mL/min of CO2. Differences in the surface functional groups and aromaticity were observed in the biochars produced from these biomasses. It was found that oxygen containing functional groups had a greater impact on π-π electron-donor acceptor interactions, whereas greater amounts of carbonyl groups increased the adsorption of compounds with electron donating groups over compounds with electron withdrawing groups. Furthermore, optimal ratios of biomass to red mud were investigated for co-pyrolysis to achieve both strong adsorptive and magnetic properties. A greater biomass content during co-pyrolysis showed greater adsorptive properties, while only a small amount of red mud, as low as 10 wt%, was sufficient to provide the desired magnetic properties. This work was able to successfully produce an adsorbent capable of adsorbing up to 32.8 mg/g of acetaminophen by co-pyrolyzing red mud and pine wood biomass at a 9:1 ratio. The resulting composite also maintained magnetic properties, allowing the adsorbent to be easily removed from water after adsorption.

Utilization of the through-space effect to design donor-acceptor systems of pyrrole, indole, isoindole, azulene and aniline.

Molecular electrostatic potential (MESP) topology analysis reveals the underlying phenomenon of the through-space effect (TSE), which imparts electron donor-acceptor properties to a wide range of chemical systems, including derivatives of pyrrole, indole, isoindole, azulene, and aniline. The TSE is inherent in pyrrole owing to the strong polarization of electron density (PoED) from the formally positively charged N-center to the C3C4 bonding region. The N → C3C4 directional nature of the TSE has been effectively employed to design molecules with high electronic polarization, such as bipyrroles, polypyrroles, phenyl pyrroles, multi-pyrrolyl systems and N-doped nanographenes. In core-expanded structures, the direction of electron flow from pyrrole units towards the core leads to highly electron-rich systems, while the opposite arrangement results in highly electron-deficient systems. Similarly, the MESP analysis reveals the presence of the TSE in azulene, indole, isoindole, and aniline. Oligomeric chains of these systems are designed in such a way that the direction of electron flow is consistent across each monomer, leading to substantial electronic polarization between the first and last monomer units. Notably, these designed systems exhibit strong donor-acceptor characteristics despite the absence of explicit donor and acceptor moieties, which is supported by FMO analysis, APT charge analysis, NMR data and λmax data. Among the systems studied, the TSEs of many experimentally known systems (bipyrroles, phenyl pyrroles, hexapyrrolylbenzene, octapyrrolylnaphthalene, decapyrrolylcorannulene, polyindoles, polyazulenes, etc.) are unraveled for the first time, while numerous new systems (polypyrroles, polyisoindoles, and amino-substituted benzene polymers) are predicted to be promising materials for the creation of donor-acceptor systems. These findings demonstrate the potential of the TSE in molecular design and provide new avenues for creating functional materials.

Modulating photophysical properties in a flexible porous host by regulating guest-assisted charge transfer interactions.

The 1D array of electron donor-acceptor chromophoric organic molecules is of paramount importance for photovoltaic, catalytic and optoelectronic applications. Herein, we report coordination driven 1D arrays of an electron-donor guest (fluorene, carbazole, dibenzofuran, and dibenzothiophene) and o-phen chelator as an acceptor in a Zn-based porous coordination polymer, {[Zn(o-phen)(ndc)]·DMF} (PCP-1). All the guest-encapsulated PCPs were characterized by performing single-crystal structure determinations and showed emission driven by charge transfer. Exciton binding energies were calculated and correlated with electron-donating capabiliities of the guest molecules.

Construction of a redox pathway through a polyoxometalate and covalent organic framework for H2O2 photosynthesis.

A novel type of electron donor-acceptor system was built from a nitrogen-rich covalent organic framework (PC) and a polyoxometalate (BW12), fabricating a composite material (BW12@PC-250), which shows significantly improved photocatalytic H2O2 yield (56.4 μM h-1) under full spectrum illumination in pure water, being about 30 times higher than that of PC. This is due to the opening of the electron and proton transport pathway between PC and BW12, which paves a new way for POMs to modulate the photocatalytic reactions of COFs.

Constructing bifunctional and robust covalent organic frameworks via three-component one-pot Doebner reaction for Cr(VI) removal

The integral part of covalent organic frameworks (COFs) is covalent bonds. Thus, stable and functional links must be developed to expand the potential applications of COFs. Herein, in situ linkage functionalization using a three-component irreversible Doebner reaction was achieved to fabricate chemically stable carboxylic acid-bearing COFs (Tp-Tta-COOH and Tp-Tapb-COOH), which have abundant chelating groups and ordered electron donor–acceptor moieties facilitating charge separation for effective Cr(VI) adsorption and photoreduction, respectively. These functionalized COFs are more effective at Cr(VI) removal via adsorption and photoreduction than their unfunctionalized counterparts (Tp-Tta and Tp-Tapb). The synergy of adsorption and photocatalysis is crucial to effectively remove Cr(VI) from aqueous solutions. This synergy empowers Tp-Tta-COOH to be used continuously for Cr(VI) removal without any elution after each cycle. Furthermore, Tp-Tta-COOH exhibits high chemical stability, durability, and recyclability. This study will promote the development of durable and useful COF materials for real-world applications.

Photocatalyst‐ and Transition‐Metal‐Free Light‐Induced Formation of Carbon‐Chalcogen Bonds

AbstractPhotoinduced chemical transformations have become a promising aspect of organic synthesis. This review focuses on the recent advancements in harnessing photoinduced processes for the formation of carbon‐chalcogen (C−O, C−S, C−Se, and C−Te) bonds under catalyst‐free conditions. These pathways typically involve either a radical mechanism or the creation of electron‐donor‐acceptor (EDA) complexes. The review explores the intricacies of the underlying mechanisms, discusses limitations, and evaluates the applicability of various methodologies in this field. Notably, photocatalyst and transition metal‐free photochemical reactions offer effective alternatives to enhance sustainability in this research area.

Effect of the charge-separated state on the 3MLCT state: Synthesis and study of the photophysics of electron donor-acceptor dyads based on Pt(II)-Schiff base coordination framework and naphthalenediimide chromophore

We prepared Pt(II)-Salen Schiff base complexes with a naphthalenediimide (NDI) unit attached on the coordination framework, to study the intersystem crossing (ISC), the charge separation, and the possible formation of a long-lived triplet charge separated (CS) state. The Pt(II)-Schiff base coordination framework acts as electron donor and it shows ultrafast ISC (<1 ps) and small Stokes shift. NDI acts as electron acceptor. The two units are attached either via a phenyl linker (Pt-NDI) or phenyl ethynyl linker (Pt-CC-NDI). Negligible electronic interaction between the Pt(II)-Schiff base coordination framework and the NDI unit at ground state was observed for both dyads, whereas the phosphorescence of the Pt(II)-Schiff base coordinated framework was quenched to large extent in the dyads, as compared to the reference complexes containing no NDI unit, especially in polar solvents. Electrochemical and optical spectral data show that the CS state energy is 1.93 eV, 1.82 eV, 1.54 eV, 1.43 eV in n-hexane (HEX), toluene (TOL), tetrahydrofuran (THF), acetonitrile (ACN), respectively. In comparison, the 3MLCT state and 3NDI state energy are 1.97 and 2.04 eV, respectively. Nanosecond transient absorption spectra show the formation of the 3MLCT state for Pt-CC-NDI, whose lifetimes is shortened in polar solvents (τT = 3.5 µs, 2.1 µs, 22 ns, and 19 ns in HEX, TOL, THF and ACN, respectively), similar trend was observed for Pt-NDI. Femtosecond transient absorption spectra show that the charge separation takes less than 1 ps both in toluene and acetonitrile. Quenching of the otherwise long-lived triplet excited state (3.5 µs) by a short lived CS state may be developed as a photo-protection mechanism similar to that found in natural photosynthetic apparatus.