Donor-acceptor Pair Research Articles

Au@NiFeMOFs as the signal quencher of Au@g-C3N4NSs composite for sensitive “on-off” electrochemiluminescence immunosensing of beta-2-microglobulin

In this study, an electrochemiluminescence resonance energy transfer (ECL-RET) immunosensor was constructed to detect beta-2-microglobulin (B2M). As a donor–acceptor pair, a carbon nitride nanosheet modified with gold nanoparticles (Au@g-C3N4NSs) and a nickel- and iron-based organic framework modified with gold nanoparticles (Au@NiFeMOFs) were prepared. The sandwich immunosensor was successfully constructed so that ECL-RET occurred between Au@NiFeMOFs and Au@g-C3N4NSs. The ECL intensity of the immunosensor decreased with the increase the B2M concentration due to the low conductivity of B2M. The linear range of the ECL-RET immunosensor was from 10 fg/mL to 10 ng/mL, and the limit of detection was 2.3 fg/mL (S/N = 3). The developed immunosensor had high sensitivity, high specificity, and excellent stability. It could realize the sensitivity test of B2M and provide a novel idea for the detection of biomarkers.

Impact of high-temperature Mg-implantation on defects and dopants distribution in GaN

We have investigated the impact of high-temperature Mg-implantation in GaN layers on distribution of Mg-enriched defects using scanning transmission electron microscopy and atom probe tomography. For this, 1 × 1019 cm−3 Mg ions have been implanted in GaN layers at room temperature (RT) and 1000 °C, followed by annealing at 1300 °C. A smaller number of Mg-enriched defects were observed in the sample implanted at 1000 °C in comparison to the sample implanted at RT. The implantation of Mg ions at 1000 °C resulted in a higher amount of randomly distributed Mg in the GaN matrix, which, in turn, leads to more uniform and enhanced donor–acceptor pair emission, leading to higher Mg activation.

High-Efficiency ZnS: Cu+, Al3+ Scintillator for X-ray Detection in a Non-Darkroom Environment.

Scintillator is a key component in X-ray detectors that determine the performance of the devices. Nevertheless, due to the interference of the ambient light sources, scintillators are only operated in a darkroom environment currently. In this study, we designed a Cu+ and Al3+ co-doped ZnS scintillator (ZnS: Cu+, Al3+) that introduces donor-acceptor (D-A) pairs for X-ray detection. The prepared scintillator displayed an extremely high steady-state light yield (53,000 photons per MeV) upon X-ray irradiation, which is 5.3 times higher than that of the commercial Bi4Ge3O12 (BGO) scintillator, making it possible in X-ray detection with the interference of ambient light. Furthermore, the prepared material was employed as a scintillator to construct an indirect X-ray detector, which performed a superior spatial resolution (≈10.0 lp/mm) as well as persistent stability under visible light interference, demonstrating the feasibility of the scintillator in practical applications. Therefore, this research presented a convenient and useful strategy to realize X-ray detection in a non-darkroom environment.

Integrating Tetrathiafulvalene and Nickel-Bis(dithiolene) Units into Donor-Acceptor Covalent Organic Frameworks for Stable and Efficient Photothermal Conversion.

Tetrathiafulvalene (TTF) and Ni-bis(dithiolene) are typical conductive units widely studied in electronics, optics, and photochemistry. However, their applications in near-infrared (NIR) photothermal conversion are often limited by insufficient NIR absorption and low chemical/thermal stability. Herein, we integrate TTF and Ni-bis(dithiolene) into a covalent organic framework (COF) with stable and efficient NIR and solar photothermal conversion performance. Two isostructural COFs, namely Ni-TTF and TTF-TTF, are successfully isolated which are composed of TTF and Ni-bis(dithiolene) units as donor-acceptor (D-A) pairs or TTF units only. Both COFs show high BET surface areas and good chemical/thermal stability. Notably, compared with TTF-TTF, the periodic D-A arrangement in Ni-TTF significantly lowers the bandgap, leading to unprecedented NIR and solar photothermal conversion performance.

D-A Structured High-Performance Photothermal/Photodynamic Thionin-Synthetic Melanin Nanoparticles for Rapid Bactericidal and Wound Healing Effects.

Synthesized melanin nanoparticles (SMNPs) are used as advanced photothermal materials. However, their internal structures are complex and disordered, and tuning the photothermal performance of nanoparticles is still a hot spot of concern. This article presents thionin (Th)-doped SMNPs, namely Th-SMNPs, which are the first SMNPs formed using the one-pot polymerization of Th with Levodopa. Th can undergo Michael addition and Schiff base reaction between indole dihydroxy/indolequinone and their oligomers to form donor-acceptor pairs in the structure to modulate the photothermal performance of SMNPs. Structural and spectroscopic analyses and density functional theory simulations further confirm the existence of the donor-acceptor structure. Th-SMNPs exhibit excellent total photothermal efficiency (34.49%) in the near-infrared region (808nm), which is a 60% improvement compared to SMNPs. This allows Th-SMNPs to exhibit excellent photothermal performance at low power 808nm laser irradiation. Meanwhile, Th not only enhances the photothermal properties of SMNPs, but also imparts photodynamic effects to SMNPs. Th-SMNPs can produce 1 O2 under 660nm laser irradiation. A dual-function photothermal and photodynamic textile named Th-SMNPs@cotton is constructed based on Th-SMNPs, which can act as a rapid photothermal/photodynamic sterilization and is promising for wound healing treatment of bacterial infections under low-power dual laser irradiation.

Analyte-Triggered Excited-State Intramolecular Proton Transfer- Delayed Fluorescence: A General Approach for Time-Resolved Turn-On Fluorescence Imaging.

The research of delayed fluorescence (DF) has been a hot topic in biological imaging. However, the development of analyte-triggered small molecule DF probes remains a considerable challenge. Herein a novel excited-state intramolecular proton transfer-delayed fluorescence (ESIPT-DF) approach to construct analyte-stimulated DF probes was reported. These new classes of ESIPT-DF luminophores were strategically designed and synthesized by incorporating 2-(2'-hydroxyphenyl)benzothiazole (HBT), a known ESIPT-based fluorophore, as acceptor with a series of classic donor moieties, which formed a correspondingly twisted donor-acceptor pair within each molecule. Thereinto, HBT-PXZ and HBT-PTZ exhibited significant ESIPT and DF characters with lifetimes of 5.37 and 3.65 μs in the solid state, respectively. Furthermore, a caged probe HBT-PXZ-Ga was developed by introducing a hydrophilic d-galactose group as the recognition unit specific for β-galactosidase (β-gal) and ESIPT-DF blocking agent and applied to investigate the influence of metal ions on β-gal activity on the surface of Streptococcus pneumoniae as a convenient tool. This ESIPT-DF "turn-on" approach is easily adaptable for the measurement of many different analytes using only a predictable modification on the caged group without modification of the core structure.

Charge Carrier Dynamics in Planar Heterojunction Organic Solar Cells

The ionization energy (IE) offset of a donor–acceptor pair provides the driving force for hole transfer and subsequent free charge carrier generation in low‐bandgap nonfullerene organic solar cells (OSCs). However, the interfacial energetic landscape in bulk heterojunction OSCs is determined by the materials’ electronic structure and intermolecular interactions at the donor/acceptor interface, causing local energy‐level shifts and disorder. Herein, the impact of the IE offset on the charge transfer efficiency and charge carrier dynamics is systematically evaluated by characterizing PM6/ITIC, PM6/IT‐2Cl, and PM6/IT‐4Cl planar heterojunction (PHJ) solar cells. Ultrafast spectroscopy and time‐resolved charge carrier density measurements reveal that an IE offset of about ≈0.5 eV leads to efficient hole transfer and subsequent free charge generation. Furthermore, bimolecular charge recombination and consequently triplet generation are significantly reduced in systems with high IE offset. This work underlines the importance of sizeable donor–acceptor IE offsets in PHJ nonfullerene OSCs as critical for high‐efficiency donor/acceptor material and device design.

Electrochemiluminescence Immunosensors Based on ECL-RET Triggering between Mn SANE/PEI-Luminol and PtCu/h-MPF for Ultrasensitive Detection of CEA.

In this paper, a novel donor-acceptor pair was creatively proposed based on the principle of electrochemiluminescence resonance energy transfer (ECL-RET): luminol immobilized on polyethyleneimine (PEI)-functionalized manganese-based single-atom nanozymes (Mn SANE/PEI-luminol, donor) and a PtCu-grafted hollow metal polydopamine framework (PtCu/h-MPF, acceptor). A quenched ECL immunosensor was constructed for the ultrasensitive analysis of carcinoembryonic antigen (CEA). Mn SANE, as an efficient novel coreaction accelerator with the outstanding performance of significantly activating H2O2 to produce large amounts of ROS, was further modified by the coreactant PEI, which efficiently immobilized luminol to form a self-enhanced emitter. As a result, the electron transport distance was effectively shortened, the energy loss was reduced, and luminol achieved a high ECL efficiency. More importantly, PtCu-grafted h-MPF (PtCu/h-MPF) was proposed as a novel quencher. The UV-vis spectra of PtCu/h-MPF partially overlap with the ECL spectra of Mn SANE/PEI-luminol, which can effectively trigger the ECL-RET behavior between the donor and the acceptor. The multiple quenching effect on Mn SANE/PEI-luminol was achieved, which significantly improved the sensitivity of the immunosensor. The prepared immunosensor exhibited good linearity in the concentration range of 10-5 to 80 ng/mL. The results indicate that this work provides a new method for the early detection of CEA in clinical diagnosis.

A potential-resolved ratiometric electrochemiluminescence aptasensor for Pb2+: Gold nanoclusters and amino-terminated perylene derivative as both emitters and resonance energy transfer donor-acceptor pair

Searching for a pair of electrochemiluminescence (ECL) emitters that can be simultaneously applied as energy donor-acceptor pair is very vital for ECL resonance energy transfer strategy (ECL-RET)-based ratiometric ECL aptasensors, as it can avoid the complex design caused by the addition of exogenous donor or acceptor. Herein, gold nanoclusters (AuNCs) with aggregation-induced emission property and amino-terminated perylene derivative (PTC-NH2) with a broad absorption range were firstly combined to generate the anodic and cathodic ECL signals, respectively. Importantly, they were also operated as a novel ECL-RET donor-acceptor pair due to their favorable spectral overlap. On this basis, a potential-resolved ratiometric ECL aptasensor was established to detect lead ions (Pb2+). Specifically, the energy of AuNCs was absorbed by PTC-NH2 in the absence of Pb2+, leading to a decrease of the anodic ECL signal and the appearance of the cathodic ECL signal. Upon the addition of Pb2+, the ECL-RET process was impeded, and the ECL signals were reversed. By measuring the ratio of AuNCs and PTC-NH2 ECL intensities, the developed ratiometric ECL aptasensor displayed a low detection limit of 0.05 pM with excellent selectivity and satisfactory stability. Finally, the proposed aptasensor presented favorable feasibility for Pb2+ assays in soil samples.

A Combination of Ion Implantation and High‐Temperature Annealing: Donor–Acceptor Pairs in Carbon‐Implanted AlN

Herein, carbon‐implanted high‐temperature annealed (HTA) AlN layers are analyzed and donor–acceptor pair (DAP) transitions probably between the two most abundant impurities, carbon and oxygen, are identified. Both are regarded as the main, hard‐to‐avoid impurities in crystal growth. Oxygen is believed to lead to absorption in the deep UV below a wavelength of 250 nm. In contrast, carbon is the most likely candidate to be responsible for a distinct absorption band around 265 nm. This interpretation has recently been challenged. In this study, carbon‐implanted and HTA AlN layers with ion fluences above 8.1 × 1015 cm−2 are analyzed using low‐temperature and time‐resolved cathodoluminescence spectroscopy. Due to the high concentration of oxygen inside the AlN, as a result of the HTA process, a DAP transition between a most likely carbon‐related acceptor and ON is observed. The measured temperature‐ and power‐dependent blueshift of the peak emission energy as well as the luminescence transients can be clearly explained by a continuous change from a DAP transition at low temperature to a free electron to acceptor transition with increasing temperature. The findings are supported by a configurational coordinate model that describes the measured behavior qualitatively.

Discrete Donor–Acceptor Pair Transitions in CH3NH3PbI3 Perovskite Single Crystals

Achieving a better understanding of the physics of defects in halide perovskites (HPs) is a key challenge for improving the efficiency of the devices. Herein, a comprehensive study of the defect emission of CH3NH3PbI3 perovskite single crystals is presented. The emission of the pristine surface of cleaved crystals is systematically investigated based on steady‐state and time‐resolved micro‐photoluminescence (micro‐PL) spectroscopy. Donor–acceptor pair (DAP) recombination is observed due to the presence of native shallow defects. The DAP spectra present an important variability depending on the location on the surface of the crystals due to inhomogeneous defect distribution. A strong blueshift of the emission is measured as a function of excitation power and is explained by fluctuating potential caused by compensated defects. With increasing photocarrier density, a transition from a structureless to a structured DAP emission with several longitudinal optical phonon replicas is observed. The DAP transition is characterized by the redshift of the emission with time and a slow, non‐exponential PL decay. Sharp discrete lines with sub‐meV widths, the most recognizable spectral signature of DAP transition, are revealed. Herein, the apparently contradictory previous observations on defect emission of CH3NH3PbI3 are reconciled by the results and new insights are provided into the properties of defects in HPs.

A Solar Responsive Battery Based on Charge Separation and Redox Coupled Covalent Organic Framework

AbstractSolar‐responsive battery holds great promise in solar‐to‐electrochemical energy storage, but is impeded by the lack of efficient photoelectrochemical‐cathodes. Herein, a crystalline mesoporous (≈4.0 nm) covalent organic framework (TA‐PT COF) with repeating units consisting of covalently linked triphenylamine (TPA) and perylenetetracarboxylic diimide (PTCDI) is presented. The repeating unit functions as both a donor–acceptor pair and a dual‐redox site to realize a molecule‐level coupling of intramolecular charge separation (τCS = 136.2 ps, τCR = 949 ps) and reversible redox chemistry (C=O/CO−, TPA/TPA+). Equipped with this photoelectrochemical cathode, a reversible aqueous solar‐responsive battery delivered a reliable voltage‐response of 376 mV, an extra round‐trip efficiency of 35% and a good light durability (500 cycles). A photo‐coupled electron/mass transfer mechanism of photoelectrons for Zn2+ storage and holes for OTf− storage is further revealed, shedding light on a new photoelectrochemical cathode design based on charge separation and redox‐coupled COF for efficient solar‐responsive batteries.

Permittivity Threshold and Thermodynamics of Integer Charge-Transfer Complexation for an Organic Donor–Acceptor Pair

Molecular charge doping involves the formation of donor-acceptor charge-transfer complexes (CTCs) through integer or partial electron transfer; understanding how local chemical environment impacts complexation is important for controlling the properties of organic materials. We present steady-state and temperature-dependent spectroscopic investigations of the p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) complexed with the electron donor and hole transport material N,N'-diphenyl-N,N'-di-p-tolylbenzene-1,4-diamine (MPDA). Equilibrium formation constants (KCT) were determined for donor-acceptor pairs dissolved in a series of solvents covering a range of values of permittivity. A threshold for highly favorable complex formation was observed to occur at ϵ ∼ 8-9, with large (>104) and small (<103) values of KCT obtained in solvents of higher and lower permittivity, respectively, but with chloroform (ϵ = 4.81) exhibiting an anomalously high formation constant. Temperature-dependent formation constants were determined in order to evaluate the thermodynamics of complex formation. In 1,2-dichloroethane (ϵ = 10.36) and chlorobenzene (ϵ = 5.62), complex formation is both enthalpically and entropically favorable, with higher enthalpic and entropic stabilization in the solvent with higher permittivity. Complexation in chloroform is exothermic and entropically disfavored, indicating that specific, inner-shell solvent-solute interactions stabilize the charge-separated complex and result in a net increase in local solution structure. Our results provide insight into how modification to the chemical environment may be utilized to support stable integer charge transfer for molecular doping applications and requiring only modest changes in local permittivity.

Interparticle energy transfer between NaNdF4 and NaYbF4 in self-assembled nanostructures

Förster resonance energy transfer (FRET) is a widely used spectroscopic technique. The development of donor–acceptor combinations is essential to advance this technique. To make the energy transfer efficiency independent of the external environment, we explored the potential of constructing donor–acceptor combinations with lanthanide ion-doped nanoparticles (LNPs), in which the 4f electrons of the lanthanide ions are shielded by the 5s and 6p electrons. Non-radiative energy transfer between LNPs was demonstrated in self-assembled nanostructures and core–shell structure of LNPs was used to control the distance between donor and acceptor in self-assembled nanostructures. The emission intensity ratio of donor and acceptor illustrates that the energy transfer efficiency decreases significantly with increasing distance and the effective energy transfer distance is 8.5 nm, showing the potential of using LNPs as donor–acceptor pairs in the construction of distance-dependent energy transfer system.

Cathodoluminescence studies of point defects in aluminum nitride

There is near-ultraviolet and yellow light absorption in AlN crystal. The defect of this absorption hampers the transmittance of ultraviolet light, which, in turn, limits the application of aluminum nitride substrate in deep ultraviolet electronic devices. In this paper, the sources of absorption defects are determined through the first principle simulation method and the cathodoluminescence test of four samples with different growth modes on two substrates. The peak positions of the two AlN grown by metal–organic chemical vapor deposition were observed at 370 and 480 nm; two AlN samples grown by hydride vapor phase epitaxy only observed luminescence near 370 nm. Through the characterization of sample components by x-ray photoelectron spectroscopy, it is speculated that O impurity component and Al vacancy in AlN crystal form donor–acceptor pairs, which are the source of 370 nm luminescence; with the increase in O concentration, a composite defect with Al vacancy is formed, which is the source of 480 nm luminescence. This is very important for further research on eliminating impurity absorption in an AlN epitaxial layer.

Ultra-sharp-Line Emission in Isotopic c-10BP

Cubic boride crystals with pure boron isotopes have attracted great attention in recent years. Here, high-quality cubic boron phosphide single crystals with isotopic 10B and a maximum width reaching 1.5 mm are grown via the high-temperature molten salt method. An interesting phenomenon that there are many discrete sharp lines in the low-temperature (4–80 K) photoluminescence spectra is observed. Besides, as temperature increases, the luminescence intensity of these sharp lines shows a nonmonotonic decay with two different trends exhibited. Based on analyses, the sharp-line emission originates from phonon-assisted donor–acceptor pair radiative recombination. The nonmonotonic decay is affected by the number of assisting phonons and the degree of thermal ionization under the effect of temperature, and the different decay trends are attributed to the effect of thermal ionization dependent on the distance between the donor and acceptor. Results obtained in this research are expected to enrich the knowledge concerning cubic boride crystals in the aspect of physical properties.

Characterization of magnesium channeled implantation layers in GaN(0001)

The effect of Mg channeled implantation into epitaxially grown gallium nitride (GaN) was studied using Hall-effect measurements, photoluminescence (PL), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and Rutherford backscattering spectroscopy (RBS). In the channeled implantation, deeper profiles were obtained with lower implantation energy and less damage compared to random implantation. The donor–acceptor pair signal at ∼3.28 eV, suggesting that Mg is activated, was confirmed by PL measurement when the ion dose and implantation energy are 1 × 1014 cm−2 and 20 keV, respectively. However, even with channeled implantation, several types of defects including point defects and oblong defects as seen in the random implantation were observed by TEM/STEM analysis. RBS analysis showed slightly worse crystal qualities in channeled implantation compared to non-implanted samples. Mg channeled implantation is useful to achieve deeper profiles (>1 μm), but further condition tuning of process will be necessary for practical application.

Sequential Deposition of Multicomponent Bulk Heterojunctions Increases Efficiency of Organic Solar Cells.

Constructing tandem and multi-blend organic solar cells (OSCs) isan effective way to overcome the absorption limitations of conventional single-junction devices. However, these methods inevitably require tedious multilayer deposition or complicated morphology-optimization procedures. Herein, sequential deposition is utilized as an effective and simple method to fabricate multicomponent OSCs with a double-bulk heterojunction (BHJ) structure of the active layer to further improve photovoltaic performance. Two efficient donor-acceptor pairs, D18-Cl:BTP-eC9 and PM6:L8-BO, are sequentially deposited to form the D18-Cl:BTP-eC9/PM6:L8-BO double-BHJ active layer. In these double-BHJ OSCs, light absorption is significantly improved, and optimal morphology is also retained without requiring a more complicated morphology optimization involved in quaternary blends. Compared to the quaternary blend devices, energy loss (Eloss ) is also reduced by rationally matching each donor with an appropriate acceptor. Consequently, the power conversion efficiency (PCE) is improved from 18.25% for D18-Cl:BTP-eC9 and 18.69% for PM6:L8-BO based binary blend OSCs to 19.61% for the double-BHJ OSCs. In contrast, a D18-Cl:PM6:L8-BO:BTP-eC9 quaternary blend of OSCs exhibited a dramatically reduced PCE of 15.83%. These results demonstrate that a double-BHJ strategy, with a relatively simple processing procedure, can potentially enhance the device performance of OSCs and lead to more widespread use.

Hydrogen-related 3.8 eV UV luminescence in α -Ga2O3

Temperature-dependent photoluminescence was used to investigate the impact of H on the optical properties of α-Ga2O3 films grown by halide vapor phase epitaxy. An additional UV luminescence line centered at 3.8 eV is observed at low temperatures, which strongly correlates with the concentration of H in the films. This luminescence line is assigned to donor–acceptor pair recombination involving an H-related shallow donor and H-decorated Ga vacancy (VGa-nH) as the acceptor, where n = 1, 2, 3. Previous reports have already suggested the impact of H on the electrical properties of Ga2O3, and the present study shows its clear impact on the optical properties of α-Ga2O3.

Force-Induced Shuttling of Rotaxanes Controls Fluorescence Resonance Energy Transfer in Polymer Hydrogels

The molecular shuttling function of rotaxanes can be exploited to design mechanoresponsive reporter molecules. Here, we report a new approach to such rotaxane-based mechanophores, in which the fluorescence resonance energy transfer (FRET) between a donor-acceptor pair is mechanically controlled. A cyclic molecule containing a green-light-emitting FRET donor connected to a red-light-emitting FRET acceptor was threaded onto an axle equipped with a quencher at its center and two stoppers in the peripheral positions. In the force-free state, the green emitter is located near the quencher so that charge transfer interactions or photo-induced electron transfer between the two moieties suppress green emission and prevent the FRET from the green to the red emitter. The mechanophore was covalently incorporated into a linear polyurethane-urea (PUU), and stretchable hydrogels were prepared by swelling this polymer with water. Upon deformation of the PUU hydrogels and under an excitation light that selectively excites the donor, the intensity of the red fluorescence increases, as a result of a force-induced separation of the green emitter from the quencher, which enables the FRET. The switching contrast is much more pronounced in the gels than in dry films, which is due to increased molecular mobility and hydrophobic effects in the hydrogel, which both promote the formation of inclusion complexes between the ring containing the green emitter and the quencher.