Electron Acceptor Groups Research Articles

Directionality and additivity effects of molecular acidity and aromaticity for substituted benzoic acids under external electric fields.

Our recent study [M. Li et al.Phys. Chem. Chem. Phys., 2023, 25, 2595-2605] unveiled that the impact of an external electric field on molecular acidity and aromaticity for benzoic acid is directional, which can be understood using changes in frontier orbitals and partial charges. However, it is unclear if the effect will disappear when substituting groups are present and whether new patterns of changes will show up. In this work, as a continuation of our efforts to appreciate the impact of external electric fields on physiochemical properties, we find that the directionality effect is still in place for substituted benzoic acid derivatives and that there exists the additivity effect with respect to the number of substituent groups, regardless of the direction of the applied field and the type of substituting groups. We confirm the findings using electron-donating and electron-accepting groups with the electric field applied either parallelly or perpendicularly to the carboxyl group along the benzene ring. The directionality and additivity effects uncovered from this work should enrich the body of our knowledge about the impact of external electric fields on physiochemical properties and could be applicable to other systems and properties as well.

Studying of 2,2′-Bipyrimidine Based Dyes Properties as Photo-Sensitizer for Dye Sensitized Solar Cells (DSSCs)

In this investigation, five novel π-new organic donor-π-acceptor dyes (D-π-A) based on 2,2′-bipyrimidines were used. For optimization and DFT research, respectively, the 6-311+G(d,p) basis set and B3LYP density functional theory were applied. In all the systems, diphenyl amine moiety acts as the electron-donor component, whereas the nitro/cyano moiety as electron acceptor (anchoring) group. In the conjugated spacer, a methyl/ethyl substituent was used to examine the impact of the auxiliary donor group. The computed HOMO-LUMO gap and the spectral data matched well. The oscillator strength (f), electron injection free energy (ΔGinject) and light-harvesting efficiency (LHE) were also computed and explained. The calculated values for the examined dye-sensitizers open-circuit photo voltage (Voc) and electron coupling constant (VRP) were also included in this research. This study demonstrates that every synthetic dye has promising potential as a dye sensitized solar cells (DSSCs) sensitizer.

Caffeic acid, a natural extract, as an activatable molecular probe for viscosity detection in a liquid system.

Liquids, functioning as nutrients and energy systems, regulate various functions during storage programs. Microenvironmental viscosity is one of the most important physical parameters associated with the extent of deterioration, and it is crucial to monitor the mutation of viscosity at a molecular level. Herein, we utilized caffeic acid (CaC), a natural product extracted from thistles, as a molecular probe for viscosity sensing. CaC contains phenol hydroxyl (electron-donor) and carboxyl (electron-acceptor) groups, with both moieties connected by conjugated single and double bonds, forming a typical twisted intramolecular charge transfer system. The fluorescent probe CaC, obtained from a natural product without any chemical processing, exhibits high sensitivity (x = 0.43) toward viscosity, with an obvious visualized turn-on signal. Moreover, it displays good photostability, selectivity, and wide universality in commercial liquids. Utilizing CaC, we have successfully visualized viscosity enhancement during the spoilage process, with a positive correlation between the degree of liquid spoilage and microenvironmental viscosity. Thus, this study will provide a convenient and efficient molecular probe for food safety inspection across the boundaries of traditional biological applications.

Dipole-moment-induced supramolecular assembly of a donor-acceptor-type molecule on a metal surface and in a crystal.

The conformation and alignment of molecules in organic materials are important because they affect the materials' bulk physical properties. Because two-dimensional (2D) materials offer a simpler model of three-dimensional (3D) materials, the conformation and alignment of molecules in 2D assemblies have been investigated at the atomic scale by scanning tunnelling microscopy (STM). However, differences in the conformation and alignment of molecules between 2D and 3D assemblies have not been clarified. In this work, the conformation and alignment of a donor-acceptor-type molecule, 4-(3,3-dimethyl-2,3-dihydro-1H-indol-1-yl)benzonitrile (IBN), are studied in 2D and 3D assemblies. Thus, the 2D assembly of IBN on the Au(111) surface was investigated by STM and the 3D assembly of IBN in a single crystal was investigated by X-ray crystallography. Our survey revealed that the conformation of IBN is planar in both 2D and 3D assemblies because of the electron-delocalised structure resulting from the electron-donating and electron-accepting groups of IBN; thus, the values of the dipole moment of IBN in 2D and 3D assemblies are essentially the same. In both the 2D and 3D assemblies, IBN molecules align to cancel out the dipole moment even though the self-assembled structures differ. In the 2D assemblies, the orientation and self-assembled structure of IBN are changed by the surface density of IBN, and they are affected by the crystal orientation and superstructure of Au(111) because of the strong interaction between IBN and Au(111). In addition, scanning tunnelling spectroscopy revealed that the coordination structure is not included in the self-assembled structure of IBN on Au(111).

Investigation of first hyper-polarisability molecular switches between enol–keto equilibrium of phenyl benzodifurantrione: a DFT-based computational study

The contrast of the second-order nonlinear optical response between the enol (anti and syn) and keto tautomeric equilibrium of 7-Phenyl-7H-benzo[1,2-b;4,5-b’]difuran-2,3,6-trione (PBDT) with donor/acceptor substitution at the para position of phenyl group have been computed involving electron correlation, frequency dispersion, and solvent polarity effects. The Hyper Rayleigh Scattering (HRS) first-hyperpolarisability contrast between the enol and keto forms for PBDT and Nitro-substituted PBDT is 3.5 and 2.8, respectively. However, in NMe2-substituted PBDT, a large contrast (12 times) of HRS first hyper-polarisability between enol (anti and syn) and keto form is observed. Present study reveals that electron donor group (–NMe2) in PBDT plays a pivotal role for obtaining very high contrast in the first hyper-polarisability (β HRS and β vec) values between the enol and keto forms compare to the electron acceptor (–NO2) group substitution at the same position. The solvent effect also plays a significant role in further improving the first hyper-polarisability value and its switching behaviour between the enol and keto forms of NMe2-PBDT. NLO switching contrast between the enol and keto forms of donor/acceptor substituted PBDT is also explained using the electronic features including UV-Vis absorption spectra, HOMO–LUMO electron densities, optical energy gaps, charge transfer contribution etc.

Influence of the cooling rate in annealing post-treatment on small molecule with siloxane side chains for solution-processed organic field-effect transistors

In this study, a donor-acceptor-type small molecule possessing a narrow bandgap with siloxane-terminated side chains, namely, S-LBG, was synthesized and characterized to be used as a semiconducting layer in organic field-effect transistors (OFETs). The diketopyrrolopyrrole (DPP)-based small molecule contains silaindacenodithiophene as an electron-donor core and 2-(1,1-dicyanomethylene)rhodanine as an electron-accepting end group. S-LBG films show highly crystalline structures after thermal annealing treatment owing to the strong intermolecular interactions between its siloxane side chains; furthermore, a smooth-surface film with a large polycrystalline grain size can be fabricated by controlling the cooling rate after annealing. Solution-processed OFETs using cooled S-LBG films at a rate of 1 °C/min and exhibits a high hole mobility of 0.102 cm2 V−1 s−1 with a π–π stacking distance of 0.659 nm.

Tuning the Electronic and Charge Transport Properties of Schiff Base Compounds by Electron Donor and/or Acceptor Groups

Organic semiconductors have gained substantial interest as active materials in electronic devices due to their advantages over conventional semiconductors. We first designed four Schiff base compounds, then the effect of electron donor/acceptor groups (methyl/nitro) was studied on the compounds' electronic and transport nature. The absorption spectra (λabs) were computed by time-dependent DFT at TD-B3LYP/6-31+G** level. The effect of different solvents (ethanol, DMF, DMSO, and acetone) was investigated on the λabs. The substitution of the -NO2 group to the furan moiety at the 5th position in Compound 3 leads to a red-shift in the absorption spectrum. A smaller hole reorganization energy value in Compound 3 would be beneficial to get the hole's intrinsic mobility. In contrast, a reduced-electron reorganization energy value of Compound 4 than hole may result in enhanced electron charge transfer capabilities. The reorganization energies of compounds 1 and 2 exposed balanced hole/electron transport probability. The optical, electronic, and charge transport properties at the molecular level indicate that Compound 3 is suitable for organic electronic device applications.

Investigation of spin-charge-structure in human heme using the DFT method

The enzyme heme oxygenase (HO) plays an essential role in the destruction of heme molecules. Heme oxygenase uses dioxygen to open the specific orientation of the porphyrin ring at the position of the [Formula: see text]-meso carbon. This reaction is called mesohydroxylation, which produces [Formula: see text]-bilirubin, and the [Formula: see text]-bilirubin produced by the second enzyme bilirubin reductase is converted into bilirubin. The destruction of heme is carried out by a special enzymatic process, and the enzymes heme oxygenase and bilirubin reductase are responsible for the enzymatic role of this process. All calculations were done using Gaussian 2003 and Gaussian 2009 on an Asus NW522 computer and with the help of the Gaussian viewer, and Hyperchem software. Calculation and optimization of different configurations of molecules using the quantum computing method from the beginning of B3LYP were performed using the 631G-basis set using the FOPT keyword. The calculation of charge and spin was done based on Mulliken’s charge and spin. The analysis of bonding orbitals (NBO) was done to fully investigate the distribution of [Formula: see text] and [Formula: see text] spins in d orbitals of iron and ring. The molecule is optimized using the quantum calculation method from the beginning, B3LYP with the basis set 6-31G. The results of DFT studies showed that the LUMO-HOMO energy gap values reflect the chemical activity of the molecule. The higher the HOMO-LUMO energy gap, the harder and more stable the molecule is and the less reactive it is. The reduction of the HOMO and LUMO energy gap explains the final charge transfer interaction that occurs inside the molecule due to the ability to accept electrons in the electron acceptor group.

The effect of electron donor and acceptor conformations on thermally activated delayed fluorescence

A novel organic molecule, 2-(9,9-dimethyl-9 H -acridin-10-yl)-anthraquinone (DMAC-AQ), is designed and synthesized by introducing a dual-conformation electron donor 9,9-dimethyl-9,10-dihydroacridine to a typical electron acceptor anthraquinone. DMAC-AQ exhibits decent thermally activated delayed fluorescence (TADF) property. However, using DMAC-AQ as an emitter, the doped and non-doped electroluminescence devices show maximum external quantum efficiency values of 5.63% and 0.32%, respectively, which are much lower than expected. Crystallographic analysis reveals that DMAC-AQ has two nearly orthogonal conformers (C1 and C2), in which planar and non-planar DMAC moieties are both linked to the AQ group with high twisting angles. Interestingly, the non-planar conformations of donor (D) and acceptor (A) units contribute to the generation of luminescent enantiomers in C2. C1 exhibits obvious TADF while C2 shows no TADF. The results suggest that nonplanar conformation of the donor in the emitter may inhibit TADF and significantly reduce device efficiency. The present work may provide new insight into understanding the effect of D and A conformations in TADF emitters. The non-planar conformations of electron donor and acceptor groups in thermally activated delayed fluorescence (TADF) emitters may inhibit TADF and significantly reduce device efficiency. • A TADF emitter with dual conformations was designed and synthesized. • The effect of donor and acceptor conformations on TADF was investigated. • Nonplanar conformation of the donor in the emitter may inhibit TADF.

Anaerobic mineralization of toluene by enriched soil-free consortia with solid-phase humin as a terminal electron acceptor

The anaerobic biodegradation of toluene proceeds very slowly owing to limited electron acceptors in contaminated aquifer. The liquid reagents traditionally used to enhance this process readily migrate away from the contaminated site, and continuous addition would cause secondary pollution. In our previous study, the reduced solid-phase humic substances (humin), which are redox active, were found to act as electron donors to promote the microbial reactions. Here, we provide new evidence that humin can promote the anaerobic biodegradation of toluene as a terminal electron acceptor. When inoculating nitrate-reducing (NR) and iron-reducing (IR) consortia with toluene degradation activities, the average toluene degradation rates reached 21.20 ± 1.18 μmol/(L·d) and 15.43 ± 0.41 μmol/(L·d) in the presence of a sediment humin (HMcj), and 94.69% ± 4.26% and 93.20% ± 3.73% of the electrons released from toluene oxidation to CO2 could be recovered by the reduction of HMcj, respectively. Spectroscopy analyses revealed that quinone moieties and nitrogen-containing moieties may be the electron-accepting groups of HMcj. Based on 16S rRNA sequencing, Cellulomonas spp. were the possible functional bacteria in the culture with NR consortium as the inoculum, while Azospira spp., Cellulomonas spp. and Bacillus spp. were the possible functional bacteria in the culture with IR consortium as the inoculum. Further Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analyses indicated that toluene oxidation and extracellular electron transfer functions were more abundant in HMcj amended cultures, suggesting a possible enhancement mechanism by HMcj. Additionally, experiments using natural groundwater illustrated that toluene degradation was highly dependent on its concentration, HMcj dosage, pH, and salinity. The study of a column filled with HMcj-coated quartz sand demonstrated a desirable level of toluene degradation in a continuous-flow mode without the presence of other electron acceptors. This study provided an effective and green approach for the remediation of the toluene-contaminated groundwater.

Planar chiral AIEgens based on [2.2]paracyclophane as efficient solid-state deep red circularly polarized luminescent emitters

In this work, a series of [2.2]paracyclophane-based 4-(dicyanomethylene) -4H-pyran compounds (2a−2d) with aggregation-induced emission (AIE) and circularly polarized luminescence (CPL) properties were designed and synthesized. These compounds exhibit orange and deep red emissive fluorescence at 585–686 nm with high fluorescence quantum yields (Φf) of 40–97% in solid-state. More importantly, (Rp)/(Sp)-2a−2b form different aggregation states due to the influence of different substituents, resulting in different Cotton effects. Moreover, (Rp)/(Sp)-2a−2b display aggregation-induced circularly polarized luminescence (AICPL) signals in the deep red region with moderate luminescence dissymmetry factors (1.4–1.9 × 10−3). These photophysical properties are rationalized by single crystal structure analysis, TD-DFT calculations, cyclic voltammetry and SEM. These results clearly demonstrate the introduction of strong electron-accepting group on [2.2]paracyclophane derivatives to enhance the ICT process is an efficient approach to construct planar chiral deep red circularly polarized luminescence emitters.

Experimental and theoretical studies of photophysical properties of N-Substituted iminocoumarins

The photophysical properties of a set of new synthesized iminocoumarins and their N-substituted dyes have been investigated by means of experimental spectroscopy and DFT and TDDFT theoretical calculations. These materials act as push-pull systems consisting of free iminocoumarins and N-substituted by the dicyanovinyl function, that bearing different electron donor and acceptor groups. All the dyes were firstly characterized by NMR and IR experimental spectroscopy. Their photophysical properties are then examined by solid state UV–Vis absorption and fluorescence. Good agreement between experimental and theoretical UV–Vis absorption features was found. The main interests revealed are the substitution and coupling effects on the light absorption and emission characteristics. Attractive and motivating findings were spelled out such a bathochromic shift, gap energy lowering and Stokes shift enhancement. The N-substitution leaded to new red emitting dyes with good stabilities that could be very interesting in optoelectronic devices applications.

Latent Carbene: Diaminomethylation of Thiophenes

AbstractThe reaction of silylformamidine with various halo‐ and ethoxycarbonyl substituted thiophenes was studied. It proceeded via C−H bond insertion of the nucleophilic diaminocarbene that exists in an equilibrium with silylformamidine affording aminals. The reaction proceeded more readily at the 2(5)‐position compared to the 3(4) one. The number of halogens at the thiophenes markedly influences the reaction. The more halogens, the higher the reaction rate. Even one electron acceptor group at the thiophene ring is enough to promote the reaction. As a rule, the reaction does not require solvents or catalysts. Hydrolyses of the aminals provides a novel convenient approach to substituted thiophene aldehydes.

Acceleration of Nonradiative Charge Recombination Reactions at Larger Distances in Kinked Donor-Bridge-Acceptor Molecules.

Photoinduced electron transfer in donor-bridge-acceptor (D-B-A) molecular systems can occur via tunneling over long distances (rDA) of well over 10 Å. We commonly observe decreasing rates of electron transfer with increasing distances, a result of a decrease in the electronic coupling of the donor and acceptor moiety. In the study of D-B-A molecules with Ru(bpy)32+ as a bridge/core, Kuss-Petermann and Wenger observed the opposite trend (J. Am. Chem. Soc.2016, 138, 1349); a maximum rate constant of electron transfer was observed at an intermediate electron transfer distance. Within the high-temperature limit of the classical Marcus equation, their observation was qualitatively explained by a sharp distance dependence of outer sphere (or solvent) reorganization energy, as predicted by Sutin and co-workers (J. Am. Chem. Soc.1984, 106, 6858), and almost distance-independent electronic couplings. Here, we report another example of such an underexplored behavior with three kinked D-B-A systems of rDA ∼ 10-19 Å, showing increasing rates of nonradiative charge recombination with increasing rDA. The three D-B-A systems are based on boron dipyrromethene and triphenylamine as electron acceptor and donor groups, respectively, with aryl bridges where the donor and acceptor moieties are connected at meso-positions. These D-B-A molecules exhibit radiative electron transfer reactions (or charge-transfer emission), which enables us to experimentally determine the solvent reorganization energy and the electronic couplings. The analysis of charge-transfer emission that explicitly considers electron-vibration coupling, in conjunction with the temperature-dependent analysis and computational method, revealed that the solvent reorganization energy indeed increases with distance, and at the same time, the electronic coupling decreases with distance expectedly. Therefore, under the right conditions for solvent reorganization energy and electronic coupling values, our results show that we can observe the acceleration of electron transfer reactions with increasing distance, even when we have the expected distance dependence of electronic coupling. This work indicates that the acceleration of electron transfer with increasing distance may be achieved with a fine-tuning of molecular design.

(2,6-Dichloro-4-iodophenyl)bis(2,4,6-trichlorophenyl)methane as a precursor in efficient cross-coupling reactions for donor and acceptor functionalized triphenylmethyl radicals

To date, the functionalization of the tris(2,4,6-trichlorophenyl)methyl radical (TTM) is restricted to strong electron donating groups, whereas other substituents give only low or no reaction yields. Here, we present the synthesis of a mono-iodized derivative of the protonated TTM precursor (HTTM). It reacts readily in various types of cross-coupling reactions to give access to triphenylmethyl radicals functionalized with the respective electron donating or electron accepting groups. Iodized HTTM overcomes current limitations in accessibility and yield for TTM radicals functionalized with weaker electron donating groups and electron accepting groups, enabling the synthesis of virtually any desired TTM radical derivative. The performance of iodized HTTM is demonstrated by the synthesis of new stable radical compounds that are otherwise not or hardly accessible. Trimethoxyphenyl is introduced as a first nitrogen-free substituent of electron donating strength comparable to carbazole or diphenylamine. As electron accepting groups, we employ motifs such as benzophenone and pyrimidine and study the respective radicals for their optical properties.

Trianionic 1,3,2-Dioxaborine-Containing Polymethines: Bright Near-Infrared Fluorophores.

Trianionic polymethines of the A'-π-A-π-A-π-A' type comprising dioxaborine rings (A) and different electron-accepting end groups (A') have been synthesized. The obtained dyes absorb and emit light in the near-infrared region with remarkably high molar attenuation coefficients (ϵ up to 495 000 M-1 cm-1 in DMF) and fluorescence quantum yields (Φf up to 0.73 in DMF). Thus, the novel trianionic dyes stand among the brightest individual fluorophores known to date - with a magnitude of fluorescence brightness (ϵ⋅Φf ) of 313 000 M-1 cm-1 in DMF. The synthesized dyes demonstrate a minor negative solvatochromism and small Stokes shifts. X-ray data reveal the nearly planar geometry of the trianionic chromophore. All the obtained compounds are stable in the solid state and in a solution, although the relative stability is much higher in polar aprotic than in protic solvents.

Linear and nonlinear absorption properties of hemicyanine dyes containing 5-(4H)-oxazolone as heterocyclic ring

A series of dyes containing electron-donating (D) and electron-accepting (A) groups connected through a π-conjugated linker were designed and their linear and nonlinear absorption properties were studied. The dyes combined 1,3-oxazol-5(4H)-one core with methoxy, methyl, phenyl, cyano, and nitro group in the para-position of a phenyl ring. Spectrally resolved two-photon absorption cross-section measurements carried out by the femtosecond Z-scan technique showed wide wavelength regions of nonlinear optical absorption. The studied compound containing the phenyl ring exhibits relatively high effective two-photon absorption cross-section equal to 772 ± 100 GM at 600 nm. The experimental optical characterization is supported by the results of electronic-structure calculations.

Evolving a novel red-emitting two-photon dye with optically tunable amino group for monitoring the degree of hypoxia during liver fibrosis

Two-photon imaging has attracted increasing attention owing to its deep tissue imaging capabilities. Therefore, many fluorophores have been developed to satisfy its requirements. However, long-wavelength emission fluorophores with an optically tunable group are rarely developed. In this study, two long-wavelength emission fluorophores with an optically tunable amino group were successfully developed by introducing strong electron acceptor and large conjugated group to the TPQL dye. TPCO2 displayed a bright red emission (λem = 638 nm, Φ = 0.15) together with high two-photon action cross section and good water solubility, which enabled higher signal-to-background ratios and deep tissue imaging. The proof-of-concept probe (TPCONO2) was successfully applied to the high signal-to-background ratio imaging of nitroreductase in liver fibrosis, further realizing diagnosis of the degree of hypoxia during liver fibrosis.

SUBSTITUTED HETEROCYCLIC CHALCONES: ELECTROCHEMICAL, SPECTROSCOPIC AND THEORETICAL STUDY

We have studied the electronic and electrochemical properties of seven substituted heterocyclic chalcones (CHL 1-6) wich are functionalized with 2-thienyl groups. The phenyl ring of the chalcone scaffold has been substituted in orto or para position with electron donnor and acceptor groups (-F, -NO2, -CH3O). The electrochemical features were analyzed by cyclic voltammetry; irreversible processes were observed and attributed to the oxidation and reduction of the 2-thienyl group and the carbonyl group of the chalcone, respectively. DFT calculations were made to gain more in-depth understanding of their electronic properties. Relatively high HOMO level and low LUMO values were calculated, Eg values computed varies between 3.0-3.29 eV. These values enable us to postulate that these type of compounds are suitable building blocks to fabricate optoelectronic devices.

Effects of Xanthene Fluorophore on Light Physical Properties and their Dyeing Performance on Modacrylic Fabrics.

We designed the new xanthene dyes by introducing the donor and acceptor group of electrons in the 5' position of the carboxyphenyl ring. These synthesized dye molecules were identified using spectroscopy. And the photophysical studies, such as solvent optimization, were further explored before and after photodegradation of all synthesized dye compounds in both states (solution and solid). The resulting dyed modacrylic fabrics and measured their K/S values, reflectance (%), solid UV absorbance, and photoluminescence. All compounds are plotted on a chromaticity map in the pink region. During photodegradation, the stability of the molecule depends on the effect of the functional groups (donor to acceptor). In this case, ln[C/C0] (%) became the decreasing sequence from an electron donor to acceptor, as the electrons followed from the donation function group to the carboxylic function group. Therefore, the electron-accepting group dyes decompose rapidly during ultraviolet radiation.