Photoexcitation dynamics and energy engineering in supramolecular doping of organic conjugated molecules

Doping and blending strategies are crucial means to precisely control the excited states and energy level in conjugated molecular systems.However,effective models and platforms are rarely proposed to systematically explore the effects of the formation of trapped doped centers on heterogeneous structures,energy level and ultrafast photophysical process.Herein,for deeply understanding the impact of molecular doping in film energy levels and photoexcitation dynamics,we set a supramolecular N-B coordination composed by the conjugated molecules of pyridine functionalized diarylfluorene(host material),named as ODPF-Phpy and ODPF-(Phpy)2,and the molecule of tris(perfluorophenyl)borane(BCF)(guest material).The generation of the molecular-level coordination bond increased the binding energy of N atoms and tuned the band-gap,leading to a new fluorescent emission center with longer excitation wavelength and emission wavelength.The intermolecular Forster resonance energy transfer(FRET)in blending flms make it present inconsistent fluorescent behaviors compared to that in solution.The charge transfer(CT)state of N-B coordinated compounds and the changed dielectric constant of blending films resulted in a large PL spectra red-shift with the increased dopant ratio,causing a wide-tunable fluorescent color.The excited state behaviors of two compounds in blending system was further investigated by the transient absorption(TA)spectroscopy.Finally,we found supramolecular coordination blending can effectively improve the films'photoluminescence quantum yield(PLQY)and conductivity.We believe this exploration in the internal coordination mechanisms would deepen the insights about doped semiconductors and is helpful in developing novel high-efficient fluorescent systems.

Rational design of biodegradable semiconducting polymer nanoparticles for NIR-II fluorescence imaging-guided photodynamic therapy

Semiconducting polymer nanoparticles(SPNs)have shown great promise in second near-infrared window(NIR-II)phototheranostics.However,the issue of long metabolic time significantly restricts the clinical application of SPNs.In this study,we rationally designed a biodegradable SPN(BSPN50)for NIR-II fluorescence imaging-guided photodynamic therapy(PDT).BSPN50 is prepared by encapsulating a biodegradable SP(BSP50)with an amphiphilic copolymer F-127.BSP50 is composed of NIR-II fluorescent diketopyrrolopyrrole(DPP)segment and degradable poly(phenylenevinylene)(PPV)segment with the ratio of 50/50.BSPN50 has both satisfactory degradability under myeloperoxidase(MPO)/hydrogen peroxide(H_(2)O_(2))and NIR-II fluorescence emission upon 808 nm laser excitation.Furthermore,BSPN50 shows good photodynamic efficacy under 808 nm laser irradiation.BSPN50 shows a faster degradation rate than BSPN100 which has no PPV segment both in vitro and in vivo.In addition,BSPN50 can effectively diagnose tumor via NIR-II fluorescence imaging and inhibit the tumor growth by PDT.Thus,our study provides a rational approach to construct biodegradable nanoplatforms for efficient tumor NIR-II phototheranostics.

One-Pot Synthesis of Axially and Centrally Chiral A-type Nanogrids

A novel type of A-type nanogrids(AGs)with axial and central chirality was synthesized via Friedel-Crafts gridization of thiophenes and difluorenyl biaromatic derivatives,yielding 9%-30%.Additionally,the effect of stereoisomers of 1,1'-binaphthyl difluorenols(BINDFOH)was investigated to demonstrate that R/S-BINDFOH is more advantageous for the synthesis of AGs than Mix-BINDFOH.Furthermore,tests on OFET memory devices showed that AGs have a larger storage window,indicating potential for data storage applications.

Bidirectionally polarizing surface chemistry of heteroatom-doped carbon matrix towards fast and longevous lithium-sulfur batteries

Herein, a bidirectional polarization strategy is proposed for hosting efficient and durable lithium-sulfur battery(Li-S) electrochemistry. By co-doping electronegative N and electropositive B in graphene matrix(BNrGO), the bidirectional electron redistribution enables a higher polysulfide affinity over its monodoped counterparts, contributing to strong sulfur immobilization and fast conversion kinetics. As a result,BNrGO as the cathode host matrix realizes excellent cycling stability over 1000 cycles with a minimum capacity fading of 0.027% per cycle, and superb rate capability up to 10 C. Meanwhile, decent areal capacity(6.46 m Ah/cm^(2)) and cyclability(300 cycles) are also achievable under high sulfur loading and limited electrolyte. This work provides instructive insights into the interaction between doping engineering and sulfur electrochemistry for pursuing superior Li-S batteries.

A feasible and effective solution-processed PCBM electron extraction layer enabling the high VOC and efficient Cu_(2)ZnSn(S, Se)_(4) devices

Photo-generated carrier recombination loss at the CZTSSe/Cd S front interface is a key issue to the opencircuit voltage(V_(OC)) deficit of Cu_(2)ZnSnS_(x)Se_(4-x)(CZTSSe) solar cells. Here, by the aid of an easy-handling spin-coating method, a thin PCBM([6,6]-phenyl-C61-butyric acid methyl ester) layer as an electron extraction layer has been introduced on the top of CdS buffer layer to modify CZTSSe/CdS/ZnO-ITO(In_(2)O_(3):Sn) interfacial properties. Based on Sn^(4+)/DMSO(dimethyl sulfoxide) solution system, a totalarea efficiency of 12.87% with a VOC of 529 m V has been achieved. A comprehensive investigation on the influence of PCBM layer on carrier extraction, transportation and recombination processes has been carried out. It is found that the PCBM layer can smooth over the Cd S film roughness, thus beneficial for a dense and flat window layer. Furthermore, this CZTSSe/Cd S/PCBM heterostructure can accelerate carrier separation and extraction and block holes from the front interface as well, which is mainly ascribed to the downward band bending of the absorber and a widened space charge region. Our work provides a feasible way to improve the front interfacial property and the cell performance of CZTSSe solar cells by the aid of organic interfacial materials.

Matrix Effect on Polydiarylfluorenes Electrospun Hybrid Microfibers: From Morphology Tuning to High Explosive Detection Efficiency

Precisely optimizing the morphology of functional hybrid polymeric systems is crucial to improve its photophysical property and further extend their optoelectronic applications. The physic-chemical property of polymeric matrix in electrospinning (ES) processing is a key factor to dominate the condensed structure of these hybrid microstructures and further improve its functionality. Herein, we set a flexible poly(ethylene oxide) (PEO) as the matrix to obtain a series of polydiarylfluorenes (including PHDPF, PODPF and PNDPF) electrospun hybrid microfibers with a robust deep-blue emission. Significantly different from the rough morphology of their poly(N-vinylcarbazole) (PVK) ES hybrid fibers, polydiarylfluorenes/PEO ES fibers showed a smooth morphology and small size with a diameter of 1∼2 µm. Besides, there is a relatively weak phase separation under rapid solvent evaporation during the ES processing, associated with the hydrogen-bonded-assisted network of PEO in ES fibers. These relative “homogeneous” ES fibers present efficient deep-blue emission (PLQY>50%), due to weak interchain aggregation. More interestingly, low fraction of planar (β) conformation appears in the uniform PODPF/PEO ES fibers, induced by the external traction force in ES processing. Meanwhile, PNDPF/PEO ES fibers present a highest sensitivity than those of other ES fibers, associated with the smallest diameter and large surface area. Finally, compared to PODPF/PVK fibers and PODPF/PEO amorphous ES fibers, PODPF/PEO ES fibers obtained from DCE solution exhibit an excellent quenching behavior toward a saturated DNT vapor, mainly due to the synergistic effect of small size, weak separation, β-conformation formation and high deep-blue emission efficiency.

Retina-inspired organic neuromorphic vision sensor with polarity modulation for decoding light information

The neuromorphic vision sensor(NeuVS),which is based on organic field-effect transistors(OFETs),uses polar functional groups(PFGs)in polymer dielectrics as interfacial units to control charge carriers.However,the mechanism of modulating charge transport on basis of PFGs in devices is unclear.Here,the carboxyl group is introduced into polymer dielectrics in this study,and it can induce the charge transfer process at the semiconductor/dielectric interfaces for effective carrier transport,giving rise to the best device mobility up to 20 cm^(2) V^(−1) s^(−1) at a low operating voltage of−1 V.Furthermore,the polarity modulation effect could further increase the optical figures of merit in NeuVS devices by at least an order of magnitude more than the devices using carboxyl group-free polymer dielectrics.Additionally,devices containing carboxyl groups improved image sensing for light information decoding with 52 grayscale signals and memory capabilities at an incredibly low power consumption of 1.25 fJ/spike.Our findings provide insight into the production of high-performance polymer dielectrics for NeuVS devices.

Two-dimensional molecular crystalline semiconductors towards advanced organic optoelectronics

The compelling demand for higher performance and lower cost in the optoelectronics industry has driven the development of organic semiconductors.Molecular crystalline semiconductors(MCSs),especially two-dimensional MCSs(2D-MCSs),possess intrinsic ordered structure,quantum confinement effect,high mobility,unique optical and electrical properties,and more ecological and cheaper production,which make great promises in high-performance optoelectronic applications.Here we provide a review of design principles and synthetic strategies for 2D-MCS materials,exploiting their potential as a revolution option in associated optoelectronic devices.The merits and limitations of each strategy are presented,and these molecular crystals are considered as a competitive choice for emerging semiconducting materials in information science.Finally,the current challenges and future perspectives in this field are also elaborated.

Conversion of hydroxide into carbon-coated phosphide using plasma for sodium ion batteries

Transition metal phosphides(TMPs)are promising candidates for sodium ion battery anode materials because of their high theoretical capacity and earth abundance.Similar to many other P-based conversion type electrodes,TMPs suffer from large volumetric expansion upon cycling and thus quick performance fading.Moreover,TMPs are easily oxidized in air,resulting in a surface phosphate layer that not only decreases the electric conductivity but also hinders the Na ion transport.In this work,we present a general electrode design that overcomes these two major challenges facing TMPs.Using metal hydroxide and glucose as precursors,we show that the metal hydroxide can be converted into phosphide whereas the glucose simultaneously decomposes and forms carbon shell on the phosphide particles under a plasma ambient.Ni2P@C core shell structures as a proof-of-concept are designed and synthesized.The in situ formed carbon shell protects the Ni2P from oxidation.Moreover,the high-energy plasma introduces porosity and vacancies to the Ni2P and more importantly produces phosphorus-rich nickel phosphides(NiPx).As a result,the Ni2P@C electrodes achieve high sodium capacity(693 mAh·g^(−1) after 50 cycles at 100 mA·g^(−1))and excellent cyclability(steady capacity maintained for at least 1,500 cycles).Our work provides a general strategy for enhancing the sodium storage performance of TMPs,and in general many other conversion type electrode materials that are unstable in air and suffer from large volumetric changes upon cycling.

Rare-earth Doped Nanoparticles with Narrow NIR-II Emission for Optical Imaging with Reduced Autofluorescence

Fluorescence imaging in the second near-infrared region(900―1700 nm, NIR-II) with a high resolution and penetration depth due to the significantly reduced tissue scattering and autofluorescence has emerged as a useful tool in biomedical fields. Recently, many efforts have been devoted to the development of fluorophores with an emission band covering the long-wavelength end of NIR-II region(1500―1700 nm) to eliminate the autofluorescence. Alternatively, we believe imaging with a narrow bandwidth could also reduce the autofluorescence. As a proof of concept, NaYF4:Yb,Nd@NaYF4 downconversion nanoparticles(DCNPs) with sharp NIR-II emission were synthesized. The luminescence of DCNPs showed a half-peak width of 49 nm centered at 998 nm, which was perfectly matched with a (1000±25) nm bandpass filter. With this filter, we were able to retain most of the emissions from the nanoparticles, while the autofluorescence was largely reduced. After PEGylation, the DCNPs exhibited great performance for blood vessel and tumor imaging in living mice with significantly reduced autofluorescence and interference signals. This work provided an alternative way for the low-autofluorescence imaging and emphasized the importance of narrow emitting rare-earth doped nanoparticles for NIR-II imaging.

Efficient X-ray luminescence imaging with ultrastable and eco-friendly copper(Ⅰ)-iodide cluster microcubes

The advancement of contemporary X-ray imaging heavily depends on discovering scintillators that possess high sensitivity,robust stability,low toxicity,and a uniform size distribution.Despite significant progress in this field,the discovery of a material that satisfies all of these criteria remains a challenge.In this study,we report the synthesis of monodisperse copper(Ⅰ)-iodide cluster microcubes as a new class of X-ray scintillators.The as-prepared microcubes exhibit remarkable sensitivity to X-rays and exceptional stability under moisture and X-ray exposure.The uniform size distribution and high scintillation performance of the copper(Ⅰ)-iodide cluster microcubes make them suitable for the fabrication of large-area,flexible scintillating films for X-ray imaging applications in both static and dynamic settings.

Dynamic room-temperature phosphorescence by reversible transformation of photo-induced free radicals

Room-temperature phosphorescence(RTP)with a dynamic feature endows organic luminescent materials with promising application in optoelectronic fields.However,it remains a formidable challenge to obtain dynamic RTP materials.Herein,we reported a strategy for dynamic RTP via reversible transformation of radicals under external stimuli.RTP gradually disappeared with continuous UV-light irradiation owing to the conversion of NDIA to NDIA^(·-)in NDIA/PVA film,which can be recovered by oxidation with oxygen.Regarding the excellent reversibility and repeatability,the potential applications for round-the-clock anticounterfeiting and tag were first demonstrated.This finding not only outlines a principle to synthesize new RTP materials with dynamic behavior,but also expands the scope of applications of dynamic RTP materials.

Halogenated Thermally Activated Delayed Fluorescence Materials for Efficient Scintillation

Organic scintillators,materials with the ability to exhibit luminescence when exposed to X-rays,have aroused increasing interest in recent years.However,the enhancement of radioluminescence and improving X-ray absorption of organic scintillators lie in the inherent dilemma,due to the waste of triplet excitons and weak X-ray absorption during scintillation.Here,we employ halogenated thermally activated delayed fluorescence materials to improve the triplet exciton utilization and X-ray absorption simultaneously,generating efficient scintillation with a low detection limit,which is one order of magnitude lower than the dosage for X-ray medical diagnostics.Through experimental study and theoretical calculation,we reveal the positive role of X-ray absorption,quantum yields of prompt fluorescence,and intersystem crossing in promoting the radioluminescence intensity.This finding offers an opportunity to design diverse types of organic scintillators and expands the applications of thermally activated delayed fluorescence.

Photoactivated organic phosphorescence by stereo-hindrance engineering for mimicking synaptic plasticity

Purely organic phosphorescent materials with dynamically tunable optical properties and persistent luminescent characteristics enable more novel applications in intelligent optoelectronics.Herein,we reported a concise and universal strategy to achieve photoactivated ultralong phosphorescence at room temperature through stereo-hindrance engineering.Such dynamically photoactivated phosphorescence behavior was ascribed to the suppression of non-radiative transitions and improvement of spin-orbit coupling(SOC)as the variation of the distorted molecular conformation by the synergistic effect of electrostatic repulsion and steric hindrance.This“trainable”phosphorescent behavior was first proposed to mimic biological synaptic plasticity,especially for unique experience-dependent plasticity,by the manipulation of pulse intensity and numbers.This study not only outlines a principle to design newly dynamic phosphorescent materials,but also broadens their utility in intelligent sensors and robotics.

In Situ Super-Hindrance-Triggered Multilayer Cracks for Random Lasing inπ-Functional Nanopolymer Films

In situ self-assembly of semiconducting emitters into multilayer cracks is a significant solution-processing method to fabricate organic high-Q lasers.However,it is still difficult to realize from conventional conjugated polymers.Herein,we create the molecular super-hindrance-etching technology,based on theπ-functional nanopolymer PG-Cz,to modulate multilayer cracks applied in organic single-component random lasers.Massive interface cracks are formed by promoting interchain disentanglement with the super-steric hindrance effect ofπ-interrupted main chains,and multilayer morphologies with photonic-crystal-like ordering are also generated simultaneously during the drop-casting method.Meanwhile,the enhancement of quantum yields on micrometer-thick films(Φ=40%to 50%)ensures high-efficient and ultrastable deep-blue emission.Furthermore,a deep-blue random lasing is achieved with narrow linewidths~0.08 nm and high-quality factors Q≈5,500 to 6,200.These findings will offer promising pathways of organicπ-nanopolymers for the simplification of solution processes applied in lasing devices and wearable photonics.

Multicolor emission from lanthanide ions doped lead-free Cs_(3)Sb_(2)Cl_(9) perovskite nanocrystals

The toxicity of lead ions has become the severe challenge for the all-inorganic lead halide p erovskite materials,although some works have rep orted the lead-free perovskite nanocrystals(NCs),the photoluminescence quantum yield(PLQY)of these materials is still unsatisfactory.Meanwhile,because the halogen ions can be easily exchanged,the controllable multicolor emission in perovskite NCs is difficult to realize in current reports.In this work,we introduced lanthanide ions into lead-free Cs_(3)Sb_(2)Cl_(9) perovskite NCs.Benefitting from the energy transfer between Cs_(3)Sb_(2)Cl_(9) perovskite NC host and lanthanide ions,the multicolor emission was realized.Based on controlling the doping concentration of Tb6(3+)and Eu~(3+)ions,the white light emission under UV excitation would be turned easily in the Tb6(3+)/Eu~(3+)codoped NCs.In addition,efficient energy transfer from perovskite NCs to Tb6(3+)or Eu~(3+)ions is beneficial to improving the optical properties of lead-free perovskite NCs,resulting in maximum PLQYs of red,green and white light emission of 22.6%,19.7%and 28.5%,respectively.Finally,a white light emitting device(WLED)was fabricated with a power efficiency of 18.5 lm/W,which presents the Commission Internationale de l'Eclairage(CIE)of(0.33,0.35).

Stable and Efficient Red Perovskite Light-Emitting Diodes Based on Ca^(2+)-Doped CsPbI_(3) Nanocrystals

α-CsPbI3 nanocrystals(NCs)with poor stability prevent their wide applications in optoelectronic fields.Ca^(2+)(1.00Å)as a new B-site doping ion can successfully boost CsPbI3 NC performance with both improved phase stability and optoelectronic properties.With a Ca^(2+)/Pb^(2+)ratio of 0.40%,both phase and photoluminescence(PL)stability could be greatly enhanced.Facilitated by increased tolerance factor,the cubic phase of its solid film could be maintained after 58 days in ambient condition or 4 h accelerated aging process at 120℃.The PL stability of its solution could be preserved to 83%after 147 days in ambient condition.Even using UV light to accelerate aging,the T_(50) of PL could boost 1.8-folds as compared to CsPbI_(3) NCs.Because Ca^(2+) doping can dramatically decrease defect densities of films and reduce hole injection barriers,the red light-emitting diodes(LEDs)exhibited about triple enhancement for maximum the external quantum efficiency(EQE)up to 7.8%and 2.2 times enhancement for half-lifetime of LED up to 85 min.We believe it is promising to further explore high-quality CsPbI_(3) NC LEDs via a Ca^(2+)-doping strategy.

A facile phototheranostic nanoplatform integrating NIR-Ⅱ fluorescence/PA bimodal imaging and image-guided surgery/PTT combinational therapy for improved antitumor efcacy

Phototheranostic with highly integrated functions is an attractive platform for cancer management. It remains challenging to develop a facile phototheranostic platform with complementary bimodal imaging and combinational therapy capacity. Herein, the small-molecule cyanine IR780 loaded liposomes have been harnessed as a nanoplatform to simultaneously realize photoacoustic(PA)/the second near-infrared window(NIR-Ⅱ) fluorescence imaging and image-guided surgery/adjuvant photothermal therapy(PTT).This nanoplatform exhibits attractive properties like uniform controllable size, stable dispersibility, NIR-Ⅱ fluorescence emission, photothermal conversion, and biocompatibility. Benefiting from the complementary PA/NIR-Ⅱ fluorescence bimodal imaging, this nanoplatform was successfully applied in precise vasculature delineation and tumor diagnosis. Interestingly, the tumor was clearly detected by NIR-Ⅱ fluorescence imaging with the highest tumor-to-normal-tissue ratio up to 12.69, while signal interference from the liver was significantly reduced, due to the difference in the elimination rate of the nanoplatform in the liver and tumor. Under the precise guidance of the image, the tumor was accurately resected, and the simulated residual lesion after surgery was completely ablated by adjuvant PTT. This combined therapy showed improved antitumor efcacy over the individual surgery or PTT. This work develops a facile phototheranostic nanoplatform with great significance in accurately diagnosing and effectively treating tumors using simple NIR light irradiation.

Stable and Efficient Red Perovskite Light-Emitting Diodes Based on Ca^(2+)-Doped CsPbI_(3)Nanocrystals

α-CsPbI_(3)nanocrystals(NCs)with poor stability prevent their wide applications in optoelectronic fields.Ca^(2+)(1.00Å)as a new B-site doping ion can successfully boost CsPbI_(3)NC performance with both improved phase stability and optoelectronic properties.With a Ca^(2+)/Pb^(2+)ratio of 0.40%,both phase and photoluminescence(PL)stability could be greatly enhanced.Facilitated by increased tolerance factor,the cubic phase of its solid film could be maintained after 58 days in ambient condition or 4 h accelerated aging process at 120℃.The PL stability of its solution could be preserved to 83%after 147 days in ambient condition.Even using UV light to accelerate aging,the T50 of PL could boost 1.8-folds as compared to CsPbI_(3)NCs.Because Ca^(2+)doping can dramatically decrease defect densities of films and reduce hole injection barriers,the red light-emitting diodes(LEDs)exhibited about triple enhancement for maximum the external quantum efficiency(EQE)up to 7.8%and 2.2 times enhancement for half-lifetime of LED up to 85 min.We believe it is promising to further explore high-quality CsPbI_(3)NC LEDs via a Ca^(2+)-doping strategy.

Amorphous vanadium oxides for electrochemical energy storage

Vanadium oxides have attracted extensive interest as electrode materials for many electrochemical energy storage devices owing to the features of abundant reserves,low cost,and variable valence.Based on the in-depth understanding of the energy storage mechanisms and reasonable design strategies,the performances of vanadium oxides as electrodes for batteries have been significantly optimized.Compared to crystalline vanadium oxides,amorphous vanadium oxides(AVOs)show many unique properties,including large specific surface area,excellent electrochemical stability,lots of defects and active sites,fast ion kinetics,and high elasticity.This review gives a comprehensive overview of the recent progress on AVOs for different energy storage systems,such as alkali metal ion batteries,multivalent ion batteries,and supercapacitors with a special focus on the preparation strategies.The basic mechanisms for energy storage performance improvements of AVOs as compared to their crystalline counterparts are also introduced.Finally,challenges faced by AVOs are discussed and future development prospects are also proposed.This review aims to provide a comprehensive knowledge of AVOs and is expected to promote the development of high-performance electrodes for batteries.