Acceptor Pair Research Articles

New Rofecoxib-Based Mechanochromic Luminescent Materials and Investigations on Their Aggregation-Induced Emission, Acidochromism, and LD-Specific Bioimaging.

Development of new mechanochromic luminescent (MCL) materials from aggregation-induced emission luminogens (AIEgens) has attracted wide attention due to their potential application in multiple areas. However, rational design and crafting of new MCL materials from the simple AIEgens skeleton is still a big challenge because of the undesirable concentration quenching effect. In this study, we have constructed a new class of MCL materials by adding one phenyl as a new rotator and incorporating one pair of electron donor (D) and acceptor (A) into the system of rofecoxib skeleton. This strategy endowed the compounds (Y1-Y8) with tunable emission behavior and some of them with the AIE effect and reversible MCL behavior. These properties may be caused by the highly twisted conformation and loosely molecular packing modes, which were elucidated clearly by analyzing the data of single-crystal X-ray diffraction, powder X-ray diffraction, and differential scanning calorimetry. Further investigation revealed that Y7 displayed acidochromic property due to the protonation of the nitrogen atom. Moreover, Y7, as a typical compound, showed its potential applications in the area of anticounterfeiting, pH sensor, and LD-specific bioimaging.

Study of the optical properties of Sb2(Se1-xSx)3 (x = 0–1) solid solutions

This study presents a detailed analysis of the optical properties of the Sb2(Se1-xSx)3 (x = 0–1) polycrystals. Four antimony selenosulfide solid solutions Sb2(Se1-xSx)3 together with Sb2Se3 and Sb2S3 were synthesized from elemental precursors at the same synthesis conditions, only varying the x = S/(Se + S) value with a step of Δx = 0.2. Successful formation of the Sb2(Se1-xSx)3 solid solutions was determined by Raman spectroscopy and X-ray diffraction. As expected for the same type of crystal structure of Sb2Se3 and Sb2S3, the bimodal behavior of Ag Raman mode in Sb2(Se1-xSx)3 was detected. Temperature and excitation power dependent photoluminescence (PL) analysis of Sb2(Se1-xSx)3 was performed in order to look into the electronic and defect structure of these promising semiconductor materials for optoelectronic applications. The shift of the near band edge PL emission in Sb2(Se1-xSx)3 towards higher energies from 1.309 eV to 1.728 eV with increasing sulfur content was detected at T = 3 K. A change in the radiative recombination mechanism was detected being of excitonic origin in samples with x ≤ 0.2 and resulting from deep donor-deep acceptor pair recombination in samples with x > 0.2.

Donor-Acceptor Pair Quantum Emitters in Hexagonal Boron Nitride.

Quantum emitters are needed for a myriad of applications ranging from quantum sensing to quantum computing. Hexagonal boron nitride (hBN) quantum emitters are one of the most promising solid-state platforms to date due to their high brightness and stability and the possibility of a spin-photon interface. However, the understanding of the physical origins of the single-photon emitters (SPEs) is still limited. Here we report dense SPEs in hBN across the entire visible spectrum and present evidence that most of these SPEs can be well explained by donor-acceptor pairs (DAPs). On the basis of the DAP transition generation mechanism, we calculated their wavelength fingerprint, matching well with the experimentally observed photoluminescence spectrum. Our work serves as a step forward for the physical understanding of SPEs in hBN and their applications in quantum technologies.

The Role of Nitrogen Dopants in ZnO Nanoparticle-Based Light Emitting Diodes.

In this work, nitrogen-doped ZnO nanoparticles were synthesized in various conditions by the gas evaporation method with DC arc plasma. Nitrogen concentrations of 6.38 × 1018 cm−3 to 2.6 × 1019 cm−3 were obtained at a chamber pressure of 150 torr, using arc currents of 20 A to 70 A. The intensities of local vibrational modes at 275 cm−1 and 581 cm−1 in the Raman spectra of ZnO nanoparticles showed a dependency on the nitrogen concentration in the ZnO nanoparticles. The ratios of donor–acceptor pair and exciton emissions in the photoluminescence spectra of nitrogen-doped ZnO nanoparticles, and the electroluminescence of light-emitting diodes based on these nanoparticles, were nearly proportional to the Raman peak’s intensity at 275 cm−1. The results indicated that the nitrogen dopants in the ZnO nanoparticles were acting as an acceptor.

Discriminative Detection of Aliphatic, Electron‐Rich and Electron‐Deficient Aromatic Volatile Organic Contaminants Using Conjugated Polymeric Fluorescent Nanoaggregates with Aggregation Induced Emission Characteristics

AbstractDiscrimination of aromatic, aliphatic volatile organic compounds (VOCs) with high sensitivity and easy operational techniques is important due to related environmental implications. Herein the development of fluorescent conjugated polymers is reported, consisting of donor–acceptor pairs and their nanoaggregates as fluorophores with differential emission behavior in the presence of aromatic, aliphatic VOCs and electron‐deficient VOCs both in aqueous solution and solid state. The polymeric network consists of fluorene moiety with dangling alkyl groups as donors and aggregation‐induced emission (AIE) active tetraphenylethylene (TPE) unit as an acceptor. The corresponding fluorescent nanoaggregates exhibit enhancement in the emission intensity owing to restriction in intramolecular motion of AIE unit in the presence of aliphatic VOCs, whereas the fluorescence enhancement is accompanied by a bathochromic shift in emission maxima in the case of aromatic VOCs owing to the conformational change in the phenyl rings of TPE unit. On the other hand, the fluorescence of nanoaggregates quenches in the presence of an electron‐deficient VOC through a possible nonradiative electron transfer. Detailed mechanistic studies are corroborated through a variety of spectroscopic, density functional theory calculations, and theoretical simulations. The discriminatory response of the polymeric nanoaggregates toward a different kind of VOCs can also be observed visually in the thin‐film state.

EPR of Type I photosynthetic reaction centers.

Light-induced reactions in photosynthetic reaction centers are initiated by the absorption of a photon, which results in the transfer of a single electron and the generation of radical ions in the donor and acceptor molecules involved in the charge-separated state. Electron paramagnetic resonance (EPR) spectroscopy is the ideal method for the study of such reactions. In addition to measuring spectra of the electron transfer cofactors in continuous light, reactions can be initiated by brief flashes of light, thereby allowing the kinetics of forward electron transfer as well as recombination reactions to be obtained. Because the donor and acceptor pairs are so closely spaced and because light induced charge separation is so rapid, the donor and early acceptors are in a quantum mechanically spin entangled state, which confers properties such as increased sensitivity, the ability to measure reactions on the nanosecond timescale, and the determination of bond angles between cofactors. Additionally, distances between pairs of cofactors can be measured by detecting the modulation of a phase shifted "out-of-phase" electron spin echo signal. In this methods article, we will describe how continuous wave EPR, time resolved EPR, and pulsed EPR can be used to measure these properties in Type I photosynthetic reaction centers. Methods of analysis are described for the bound electron transfer cofactors in the heterodimeric Photosystem I reaction center of plants and cyanobacteria and in the homodimeric reaction centers found in phototrophic members of the phyla Bacillota, Chlorobiota, and Acidobacteriota.

Near-infrared photothermal conversion properties of carbazole-based cocrystals with different degrees of charge transfer

Three charge transfer carbazole-based cocrystals were obtained and demonstrated regulated photothermal conversion efficiency by the modulation of the charge transfer degree via intelligent design of donor–acceptor pairs.

Mechanisms of long-distance allosteric couplings in proton-binding membrane transporters.

Membrane transporters that use proton binding and proton transfer for function couple local protonation change with changes in protein conformation and water dynamics. Changes of protein conformation might be required to allow transient formation of hydrogen-bond networks that bridge proton donor and acceptor pairs separated by long distances. Inter-helical hydrogen-bond networks adjust rapidly to protonation change, and ensure rapid response of the protein structure and dynamics. Membrane transporters with known three-dimensional structures and proton-binding groups inform on general principles of protonation-coupled protein conformational dynamics. Inter-helical hydrogen bond motifs between proton-binding carboxylate groups and a polar sidechain are observed in unrelated membrane transporters, suggesting common principles of coupling protonation change with protein conformational dynamics.

ORBITAL INTERACTIONS AND STABILIZATION ENERGIES OF METHYL 5-6 DIHYDRO BENZO(H) QUINOLINE-4-CARBOXYLATE

Quinolines are aromatic compounds consisting of benzene rings with a pyridine heterocyclic system. In this study, the structure and orbital interactions of the methyl 5-6 dihydro benzo(h) quinolone-4-carboxylate (MDQC) molecule, which is a quinoline derivative, were analyzed. In the calculation using the B3LYP/6-311++g(d,p) level, three conformers were found in the minimum energy state according to the O=C-O-C dihedral angle scan. The energy difference (E+ZPV) between the conformers was calculated ca. 1.9 and 34.8 kJ mol-1, respectively. The relative stability of the conformers was explained using the natural bond orbital (NBO) method and performed. The Fock matrix equation calculated donor and acceptor pairs and orbital energies for NBO pairs for the most stable conformer (MDQC-1). Dominant orbital interactions of selected NBOs for MDQC-1 were calculated at the theory level B3LYP/6-311++g(d,p) and plotted. The molecular electrostatic potential (MEP) surfaces were calculated by the DFT/B3LYP/6-311++g(d,p) method and drawn. NBO charges were calculated for MDQC-1 and MDQC-2 and analyzed.

Charge carrier dynamics and photovoltaic properties of near-infrared absorbing squaraine incorporated solution-processed additive-free PTB7:PCBM based ternary solar cells

The introduction of a third component vehemently modifies the morphology and charge carrier dynamics in the blend of a donor–acceptor pair, thereby affecting the photovoltaic properties of organic solar cells (OSCs). Combining steady-state, impedance, and transient spectroscopic measurements, photovoltaic properties of 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (SQ) incorporated additive-free PTB7:PC70BM OSCs are assessed. As observed from steady-state measurements, concomitant enhancement in open-circuit voltage (VOC) and short-circuit current density (JSC) has caused a 33% enhancement in power conversion efficiency (PCE) with good reliability and reproducibility. On introducing 25 wt.% SQ to the OSCs, V OC has increased from 0.74 to 0.80 V, while J SC has improved from 11.3 to 13.9 mA cm−2 with an increment in exciton dissociation probability rate from 81.5% to 94.9%. However, the fill factor values show inconsistent marginal variations with SQ addition. Equivalent circuit modeling of bias-voltage dependent impedance spectra along with transient photovoltage measurements reveal an improvement in effective charge carrier lifetime for the SQ incorporated OSCs, in comparison to the binary device. The addition of SQ also ensures better charge transport and extraction, as evidenced by photo-CELIV and transient photocurrent analysis. Atomic force microscopy (AFM) images confirm the effective tuning of the morphology of the active layer when SQ is introduced into the binary blend, favoring efficient charge dissociation and transport. The possible operation mechanism of SQ incorporated ternary OSCs is proposed based on photoluminescence and AFM measurements. Moreover, the un-encapsulated OSC with 25 wt.% SQ has retained 91% of the initial PCE, while for the binary device the PCE declined to ∼75% of the initial value after 200 h of continuous 1 sun illumination from a white LED in ambient atmosphere.

Si−doped In0.145Ga0.855As0.123Sb0.877: A novel p−type quaternary alloy with high crystalline quality

Antimonide−based p−n junctions are particularly attractive for a wide variety of optoelectronic applications in the near and mid-infrared wavelength range. In this work, novel p−type Si−doped In0.145Ga0.855As0.123Sb0.877 epitaxial layers were grown on GaSb(100) substrates by Liquid Phase Epitaxy (LPE) technique. The XPS spectra measured on Si−doped In0.145Ga0.855As0.123Sb0.877 layers indicate that Si atoms behave as acceptors. The analysis of the surface depletion region and its relationship with phonon−plasmon L_ coupling were investigated using Raman spectroscopy, giving an acceptor concentration of NA ∼ 5.8 × 1017 cm−3 for a depletion region thickness of d ∼ 9.4 nm. Low temperature photoluminiscence (PL) spectrum for the Si−doped In0.145Ga0.855As0.123Sb0.877 layers showed a bound excitonic emission peak associated to neutral Sb acceptors, with an activation energy of ∼10meV and a donor−acceptor transition. It was observed that the Si doping reduces the excitonic emission intensity and increases the donor−acceptor pair recombination intensity.

Regenerative Flexible Upconversion-Luminescence Biosensor for Visual Detection of Diethylstilbestrol Based on Smartphone Imaging.

Diethylstilbestrol (DES), an endocrine disrupting chemical, has been linked to serious health problems in humans. In this work, a regenerative flexible upconversion-fluorescence biosensor was designed for the detection of DES in foodstuffs and environmental samples. Herein, amino-functionalized upconversion nanoparticles (UCNPs) were synthesized and immobilized on the surface of a flexible polydimethylsiloxane substrate, which was further modified with complementary DNA and dabcyl-labeled DES aptamer. The fluorescence resonance energy transfer (FRET) system was established for DES detection between dabcyl and UCNPs as the acceptor and donor pairs, respectively, which resulted in the quenching of the upconversion luminescence intensity. In the presence of a target, the FRET system was destroyed and upconversion fluorescence was restored due to the stronger affinity of the aptamer toward DES. The designed biosensor was also implemented in a dual-mode signal readout based on images from a smartphone and spectra from a spectrometer. Under the optimized experimental conditions, good linear relationships were achieved based on imaging (y = 53.055x + 36.175, R2 = 0.9851) and spectral data (y = 1.1582x + 1.9561, R2 = 0.9897). The designed biosensor revealed great practicability with a spiked recovery rate of 77.91-97.95% for DES detection in real environment and foodstuff samples. Furthermore, the proposed biosensor was regenerated seven times with an accuracy threshold of 80% demonstrating its durability and reusability. Thus, this biosensor is expected to be applied to point-of-care and on-site detection based on the developed portable smartphone device and android application.

Visible-Light-Promoted Oxidative Annulation of Naphthols and Alkynes: Synthesis of Functionalized Naphthofurans.

A visible-light-mediated site-selective oxidative annulation of naphthols with alkynes for the synthesis of functionalized naphthofurans has been developed. The reaction relies on the in situ formation of an electron donor acceptor pair between phenylacetylene and thiophenol as the light-absorbing system to obviate the requirement of an added photocatalyst. The protocol facilitates the transformation of 1-naphthol and 2-naphthol as well as 1,4-naphthoquinone into a wide variety of highly functionalized naphthofurans.

Effects of the sequential implantation of Mg and N ions into GaN for p-type doping

The sequential implantation of Mg and N ions into GaN was investigated using conventional rapid thermal annealing and ultra-high-pressure annealing (UHPA). In cathodoluminescence, the green luminescence related to nitrogen vacancies (VNs) was mostly suppressed at the Mg/N ratio of 0.5–1.0, whereas the donor–acceptor pair (DAP) emission as a signature of Mg acceptors was maintained high. The excess N implantation reduced the DAP emission through the formation of nonradiative recombination centers. The combined process of optimal Mg/N implantation and UHPA at 1673 K improved ohmic contacts by increasing Mg concentration and suppressing VNs near the surface.

Evaluating the merit of a syringol derived fluorophore as a charge transfer probe for detection of serum albumins

In this article a syringol-π-benz[e]indolium based donor–acceptor fluorophore has been reported. The fluorophore shows a solvent polarity dependent change in the absorption and emission spectra in solution. A combined spectroscopic and time dependent density functional theory (TDDFT) studies reveal higher dipole moment of the fluorophore in the excited state, resulting positive solvatochromism. In physiological pH, the phenol group in the fluorophore is easily deprotonated owing to the electron pulling effect of the substituents. Consequently, the phenolate (PhO-) becomes a strong active donor in the new donor–acceptor pair. In aqueous solution, the new phenolate fluorochrome shows negligible fluorescence due to energy loss via non-radiative pathways from the low-lying polar excited states. The fluorochrome can detect human and bovine serum albumins in physiological buffer solution with high selectivity. The underlying mechanism of human serum albumin (HSA) detection was estimated to be strong (1.46 × 105 M−1, ΔG = −7.05 kcal/mol) supramolecular complexation between the fluorophore and albumin in hydrophobic binding site III-B. The linear relationship between fluorescence intensity and HSA concentration extends from 40 mg/L to an impressive upper limit (540 mg/L), thereby opening an opportunity for albumin detection in a broad range of health conditions. The practical applicability of the fluorophore was tested in spiked urine samples and a good correlation was observed between fluorescence intensity and the concentration of human serum albumin in neutral aqueous samples.

Donor-Acceptor Pairs in Covalent Organic Frameworks Promoting Electron Transfer for Metal-Free Photocatalytic Organic Synthesis.

The donor-acceptor-type covalent organic frameworks (COFs) have recently gained increasing interest in photocatalysis, but the photoinduced electron-transfer regimes in the COFs are underexplored. Herein, we demonstrate a designed porphyrinic COF possessing a donor-acceptor structure together with its photocatalytic performance in aerobic coupling of primary amines. The COF could be photoexcited by the full range of visible light to generate electron-hole pairs that could be separated by donor-acceptor pairs. Electron transfer as the mechanism of the reaction from anthracene unit to porphyrin unit was revealed by natural transition orbitals analyses. The electrons migrate to the adsorbed O2 to generate reactive oxidative species. The COF displays remarkable photocatalytic activities in the coupling of amines to imines, which can be explained mainly by the sufficient charge separation and mobility, benefiting from the donor-acceptor pairs in the COF and their interactions to the reactants and intermediates.

Multihole models for deterministically placed acceptor arrays in silicon

We compute the electronic structure of acceptor clusters in silicon by using three methods to include electron correlations: the full configuration interaction, the Heitler-London approximation, and the unrestricted Hartree-Fock method. We show both the HL approach and the UHF method are good approximations to the ground state of the full CI calculation for a pair of acceptors and for finite linear chains. The total energies for finite linear chains show the formation of a 4-fold degenerate ground state when there is a weak bond at the end of the chain, which is shown to be a manifold of topological edge states. We identify a change in the angular momentum composition of the ground state at a critical pattern of bond lengths and show it is related to a crossing in the Fock matrix eigenvalues. We also test the symmetry of the UHF solution and compare it to the full CI; the symmetry is broken under almost all the arrangements by the formation of a magnetic state in UHF, and we find further broken symmetries for some particular arrangements related to crossings or potential crossings between the Fock-matrix eigenvalues. We also compute the charge distributions across the acceptors obtained from the eigenvectors of the Fock matrix: with weak bonds at the chain ends, two holes are localized at either end of the chain while the others have a nearly uniform distribution over the middle; this implies the existence of the non-trivial edge states. We apply the UHF method to treat an infinite linear chain with periodic boundary conditions. We find the band structures in the UHF approximation and compute the Zak phases for the occupied Fock-matrix eigenvalues; we find they do not correctly predict the topological edge states in this interacting system. We find direct study of the quantum numbers characterising the edge states provides a better insight into their topological nature.

Abnormal negative thermal quenching of photoluminescence in CdMnTe:In crystals

Temperature-dependent photoluminescence (PL) properties of indium-doped CdMnTe (CMT:In) crystals were investigated. Four emission peaks of the tip crystal and three emission peaks of the tail crystal from as-grown CMT:In ingot were observed at low-temperature (10 K) PL spectra, respectively. From 20 K to 40 K, PL intensity of the deep defect-related emission peak ( D complex ) increased with temperature, showing a negative thermal quenching effect for the tip crystal. Interestingly, from 60 K to 80 K, negative thermal quenching phenomena were found for three emission peaks, the neutral donor–bound exciton ( D 0 , X ), the donor–acceptor pair DAP and D complex , in PL spectra of the tail crystal. ICP-MS test, IR transmittance, I–V measurement and IR microscope revealed that the CMT:In crystals with many impurities and defects tended to cause abnormal photoluminescence. Specially, impurities mainly resulted in the formation of intermediate states and were responsible for the negative thermal quenching behavior. The abnormal PL behavior can be explained by intermediate states. • Temperature-dependent photoluminescence properties of indium-doped CdMnTe crystals were investigated. • Negative thermal quenching behavior existed in the range of 20~40 K and 60~80 K for tip and tail crystals, respectively. • Impurities and lattice defects related to intermediate states were responsible for the negative thermal quenching behavior.

A "turn-on" FRET aptasensor based on the metal-organic framework-derived porous carbon and silver nanoclusters for zearalenone determination

Zearalenone (ZEN) is a fungal secondary metabolite with an estrogen-like structure. Its widespread existence and potential hazards to human and animal health call for alternative rapid determination methods to monitor ZEN in food and the environment. Herein, a robust and enzyme-free "turn-on" aptasensor based on fluorescence resonance energy transfer (FRET) was developed for the sensitive identification of ZEN. Aptamer-modified silver nanoclusters (AgNCs) and porous Fe3O4/carbon octahedra derived from the metal-organic framework (MOF) acted as the FRET energy donor−acceptor pair in fluorescence quenching. DNA-templated AgNCs can be adsorbed onto the surface of porous Fe3O4/carbon octahedra through π-π stacking, which will lead to the FL quenching of AgNCs. However, in the presence of the ZEN, the formation of the ZEN/aptamer complex promoted the release of AgNCs and thereby brought about the recovery of fluorescence, which can be used to indicate the concentration of ZEN. The prepared aptasensor was characterized by various physicochemical techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), energy-dispersive X-ray spectrometry (EDX), X-ray photoelectron spectroscopy (XPS) and circular dichroism spectroscopy (CD). By combining the excellent quenching properties and easy separation of magnetic porous Fe3O4/carbon octahedra, as well as the appealing photostability and water solubility of AgNCs, the proposed FRET platform demonstrated superior analytical performance with a linear range of 0.01–250 ng mL−1 and a LOD as low as 2 × 10−3 ng mL−1. Most importantly, the practicability and reliability of the FRET-based strategy were confirmed by conducting the determination of ZEN in real samples.

Review: materials and modelling for organic photovoltaic devices

AbstractThis review gives a simple and pedagogical introduction to the field of materials and their modelling for the active layer in organic photovoltaic devices. It gives a perspective on past work and a summary of the current state of the art. Given the extremely fast changes on‐going in this field, it is hoped that this contribution will serve as both a timely snapshot and a pedagogical entry point to this fascinating subject. Furthermore, an example is given of how modelling can enhance the understanding of the structures and qualities of materials using a leading low‐bandgap polymer donor and non‐fullerene acceptor pair (PM6 and Y6). © 2021 Society of Industrial Chemistry.