Organic diradicaloids have unusual open-shell nature and properties and are promising materials for organic electronics, spintronics, energy storage and nonlinear optics. In this review, we focus on indeno-type organic diradicaloids and summarize their molecular design and synthesis, as well as topological structures, open-shell characters and diradical properties. The molecular systems are classified into indenofluorenes and diindenoacenes, indeno-based molecules with one-dimensional, two-dimensional and unique topological structures, and heterocyclic indeno-based molecules. By constructing these various topological π-skeletons with tunable conjugation modes and variation of atomic composition, their key open-shell parameters, such as diradical characters and singlet-triplet energy gaps, along with the optical, electronic and magnetic properties, as well as stabilities are efficiently modulated. More attention may be paid to accurate computational analysis, rational design and synthesis, and novel functions of indeno-type diradicaloids, which will promote the development of radical chemistry and materials.

Organic radicals with unpaired electrons have shown great semiconducting properties with potential applications in the field of organic photodetectors, organic light-emitting diodes and organic spintronics. A major problem for limiting radicals from laboratory research to practical applications is the relatively low chemical and physical stabilities. Therefore, the right selection of radical core is the key to meaningful scientific research. Phenoxyl radical is one of the few stable radicals with spin distribution properties. Moreover, phenoxyl diradicals provide extract stability due to multiple resonance structures. Due to the long-distance spin distribution, which makes phenoxyl diradicals show interesting electronic and magnetic properties. In this review, we summarize the progress of phenoxyl diradicals in recent years in terms of syntheses, properties and future perspective.

Perovskite solar cells(PSCs) have attracted tremendous attention due to their outstanding performance within a short development. Radical molecules with unpaired single electrons have been widely used in energy-related fields, such as organic light-emitting diodes(OLEDs), organic field-effect transistors(OFETs), organic and dye-sensitized solar cells, batteries, thermoelectric conversion devices, etc. However, as far as we know, there has never been a systemic collection and analysis of the application of radical molecules in PSCs. Herein, we summarized the role of the radical molecule on perovskite(passivate trap defects, enhance oxygen stability and make perovskite band-bending) and charge transport layer(improve conductivity and mobility, enhance oxygen stability, modulate work function and decrease by-product generating). Meanwhile, future directions of making full use of radical molecules in improving the performances of PSCs were envisioned.

Due to their unique physicochemical properties, the anion radical and dianion of perylene diimide derivatives(PDIs) recently attracted significant attention for organic semiconductors. However, the impact of packing structure and the radical content for carrier transport in the solid state still need to be determined. Bringing the electron-withdrawing groups is an effective strategy for enabling π−π stacking distance. Here, bay-tetrachloro-substituted PDI(B-4Cl-PDI) anion radical and dianion films were fabricated quantitatively doped with N₂H₄·H₂O. The radical contents were quantitatively calculated by absorption spectra in different doping ratios. The X-ray powder diffraction patterns showed that the anion radical presented a crystalline structure, and dianion aggregates exhibited an amorphous structure. With precise manipulation of the radical content, the anion radical aggregates and dianion aggregates showed the maximum electrical conductivity value of 0.024 and 0.0018 S/cm, respectively. The experiment results show that doping level and aggregate structure play a crucial role in electronic transport properties.

Stable neutral luminescent radicals with unpaired electrons exhibit unique spin-allowed doublet-doublet transitions, which has attracted significant attention. Although they are pure organic molecules without metal ions thus thought to have low biological toxicity, the application of luminescent radicals to bioimaging has rarely been reported. Here, a stable radical with efficient near-infrared(NIR) emission and good photostability was designed and synthesized. After being wrapped into nanoparticles, it was applied to cell fluorescence imaging. The cytotoxicity experiments suggested that the nanoparticles have remarkable biocompatibility and excellent stability. An NIR fluorescent signal was successfully observed in the cytoplasm of HCT116 cells. The experimental results gave the first example of NIR emitting radical nanoparticles for cell fluorescence imaging and proved the feasibility of the application of luminescent radicals to fluorescence imaging.

Luminescent open-shell organic radicals have recently been regarded as one of the most potential materials in organic light-emitting diodes(OLEDs). Herein, we have synthesized two new organic radicals, namely tris{4-[4-(tert-butyl)phenoxy]-2,6-dichlorophenyl}methane radical(TTM-O) and tris(4-{[4-(tert-butyl)-phenyl]thio}-2,6-dichlorophenyl)methane radical(TTM-S), by the substitution of chalcogen atom elements at the para position of conventional tris(2,4,6-trichlorophenyl)methyl(TTM) radical moiety. Interestingly, both TTM-O and TTM-S exhibited significantly enhanced photostability compared with the unsubstituted TTM radical parent. Moreover, the chalcogen atom also had a crucial impact on the photoluminescence quantum yield(PLQY) of the radicals, i.e., the PLQY of TTM-S was greatly enhanced compared to TTM radical while TTM-O was nearly non-emissive. Particularly, TTM-S showed intense PLQY of 37.54% and 185-fold longer photostability than that in cyclohexane solution of TTM.

The geometries and electronic structures of a series of electron donor-acceptor radical molecules have been studied theoretically. The computational results show that the introduction of substituents with strong electron donating ability into tri-(2,4,6-trichlorophenyl) methyl(TTM) radicals enables the radical molecules to form the non-Aufbau electronic structure. The difficulty of forming the non-Aufbau electronic structure decreases with the enhancement of the electron donating ability of the substituent, but the expansion of the molecular conjugated system is not conducive to the formation. The hybridization of different fragments in molecular orbitals results in the disproportionation of orbital energy level and forms a staggered energy level structure. The electronic structure of radical molecules can be adjusted by substituents and molecular skeleton profoundly, which is a very effective means for molecular design.

A highly persistent benzoanthracenyl radical(BAR1) protected by five substituents at strategic positions is synthesized. BAR1 exhibited half-life time of 108 h in air-saturated solution, which allowed for detailed characterization in the solution. The combined experimental and theoretical study reveals the properties associated with its asymmetric structure and spin distribution. One-electron oxidation of BAR1 afforded stable cationic species BAR1⁺, whose structure is unambiguously determined by the NMR spectroscopy.

By combining stable radical tetramethylpiperidine nitrogen oxide(TEMPO) as end groups and perylene bisimide(PBI) as the core, a small molecular cathode interlayer(CIL) (PBI-TEMPO) was synthesized. Detailed physical-chemical characterizations indicate that PBI-TEMPO can form smooth film, owns low unoccupied molecular orbital(LUMO) level of −3.67 eV and can reduce the work function of silver electrode. When using PBI-TEMPO as CIL in non-fullerene organic solar cells(OSCs), the PM6:BTP-4Cl based OSCs delivered high power conversion efficiencies(PCEs) up to 17.37%, higher than those using commercial PDINO CIL with PCEs of 16.95%. Further device characterizations indicate that PBI-TEMPO can facilitate more efficient exciton dissociation and reduce charge recombination, resulting in enhanced current density and fill factor. Moreover, PBI-TEMPO displays higher thermal stability than PDINO in solution. When PBI-TEMPO and PDINO solution were heated at 150 °C for 2 h and then were used as CIL in solar cells, PBI-TEMPO-based OSCs provided a PCE of 15%, while PDINO-based OSCs only showed a PCE of 10%. These results demonstrate that incorporating TEMPO into conjugated materials is a useful strategy to create new organic semiconductors for application in OSCs.

Oxygen evolution reaction(OER) plays a key role in the electrochemical conversion and storage processes, but the sluggish kinetics of OER strongly impedes its large-scale applications. We herein reported the in situ growth of Fe-benzenedicarboxylate(Fe-BDC) on Co(OH)₂ nanoplates[Fe-BDC/Co(OH)₂] that showed remarkably enhanced OER activity than the pristine Co(OH)₂. The incorporation of Fe species could enhance the intrinsic OER activity of Co and BDC could increase the electrochemically active surface area(ECSA), thus resulting in dramatically enhanced OER activity. In situ Raman spectroscopy characterization disclosed that Fe-CoOOH reconstructed from Fe-BDC/Co(OH)₂ was the real active site for OER. This work highlights the significance of rational tailoring of the nanostructure and electronic structure of Co(OH)₂ and provides more opportunities for its widespread applications.

Understanding the quantum effect in the cross-conjugated system is of fundamental significance in molecular electronics. In this study, four molecules Xa-O, Xa, BP and BP-O were synthesized to investigate the destructive quantum interference(DQI) of a carbonyl bridge. The single-molecule conductance measured by the scanning tunneling microscope break junction(STM-BJ) technique demonstrates an increase in the conductance from molecule BP-O to molecule Xa-O as the cross-conjugated system is extended. Theoretical calculations show that the explicit DQI feature is presented in BP-O but absent in Xa-O, which indicates the removal of DQI in the restrained structures and results in the conductance enhancement in Xa-O.

Ferroelectric polymers, such as poly(vinylidene fluoride-trifluoroethylene)[P(VDF-TrFE) or PVTF] have attracted growing interest in developing flexible devices because of their excellent ferroelectricity and piezoelectricity. High coercive field(E _c) inherent to PVTF for switching its polarization, however, is not beneficial for practical memory or sensor device application. Different strategies, including irradiation and interface control, have been thus developed to reduce E _c. Despite many efforts, a facile approach to tailoring intrinsic E _c of PVTF has not been documented. In this work, an optically controlled E _c was reported, which is achieved for the first time by introducing photosensitive MAPbI₃ nanocrystals into PVTF matrix. When exposed to the irradiation of 532 nm laser light, a decreased E _c of the composites can be achieved reversibly by increasing the light density. The decreased level of E _c increases as the MAPbI₃ content enhanced, and a 10.7% reduction of E _c can be achieved in 15%(mass fraction) MAPbI₃/PVTF samples. These results could be attributed to loading an internal stress on PVTF, which was generated by the photostriction of MAPbI₃ nanocrystals. This explanation was further supported by in-situ XRD results under irradiation of 532 nm laser light. Our findings may offer the opportunity to optically modulate the ferroelectric properties of PVTF composites for optimized device performances.

Natural plants and Chinese herbal medicines are valuable resources. It is one of the new tasks for medical workers to study the new application fields of these resources. In this work, one kind of traditional Chinese herbal plant, Alisma, was chosen as a carbon source to synthesize the carbon dots(CDs). This kind of CDs has an amorphous carbon structure and shows strong stability to time, temperature, and ion strength. The results show that the degradation efficiency of malachite green dye can reach 100% in 4.5 h without illumination, and the degradation efficiency is better than that in dark environment. In addition, the CDs have also been successfully applied to HeLa cell imaging. Simple synthesis method, stable properties, good photodegradation and bioimaging applications make this material of great application value.

AFe₂O₃-MWNTs(multi-walled carbon nanotubes) composite with a reinforced concrete structure was fabricated employing a two-step method which involves a sol-gel process followed by high-temperature in situ sintering. This Fe₂O₃-MWNTs composite, intended to be used as an anode material for lithium-ion batteries, maintained a reversible capacity as high as 896.3 mA·h/g after 100 cycles at a current density of 100 mA/g and the initial coulombic efficiency reached 75.5%. The rate capabilities of the Fe₂O₃-MWNTs composite, evaluated using the ratios of capacity at 100, 200, 500, 1000, 2000 and 100 mA/g after every 10 cycles, were determined to be 904.7, 852.1, 759.0, 653.8, 566.8 and 866.3 mA·h/g, respectively. Such a superior electrochemical performance of the Fe₂O₃-MWNTs composite is mainly attributed to the reinforced concrete construction, in which the MWNTs function as the skeleton and conductive network. Such a structure contributes to shortening the transport pathways for both Li⁺ and electrons, enhancing conductivity and accommodating volume expansion during prolonged cycling. This Fe₂O₃-MWNTs composite with the designed structure is a promising anode material for high-performance lithium-ion batteries.

With the excessive consumption of fossil fuels and the massive emission of CO₂, it has led to a series of environmental crises posing a serious threat to sustainable development. Electrochemical CO₂ reduction reaction (CO₂RR) to ethylene helps solve these serious environmental crises. Herein, we report the synthesis of a copper-based electrocatalyst by pyrolysis of yolk-shell structured HKUST-1 with partial substitution of trimesic acid by benzimidazole(nitrogen source). The electrocatalyst exhibits an ethylene Faradic efficiency(FE) of 25.8% and a partial ethylene current density of 23.7 mA/cm², in addition, the electrocatalyst can maintain stable performance during 10 h of electrolysis, which are all better than those of the electrocatalyst without nitrogen dopant. According to electrochemical measurements and X-ray photoelectron spectroscopy(XPS), we propose that the nitrogen dopant plays an effective role in stabilizing Cu(I) species and promoting CO₂ molecules activation, as well as suppressing the reduction of Cu(I) species during electrolysis. Eventually, the performance of the electrocatalyst toward CO₂RR is studied in a flow cell. This work provides a new route for the design of Cu-based electrocatalyst toward electrochemical CO₂ conversion into ethylene.

In this work, we prepared a material with magnetic nanoparticles (Fe₃O₄) as core, layered double hydroxides(LDHs) as affinity shell, and cerium dioxide(CeO₂) as functional molecules(denoted as Fe₃O₄@LDH-CeO₂). On the basis of combined immobilized metal ion affinity chromatography(IMAC) and metal oxide affinity chromatography(MOAC), Fe₃O₄@LDH-CeO₂ was used to enrich phosphopeptides with high efficiency. The material exhibited high selectivity(α-casein:β-casein:BSA=1:1:5000, mass ratio), high recovery(95.87%), and good reusability of 10 times adsorption-desorption experiments. The feasibility of Fe₃O₄@LDH-CeO₂ was further investigated by extracting phosphopeptides from biological samples(nonfat milk, serum, saliva, and A549 cell lysate).

High-resolution liquid chromatography separation is essential to in-depth proteomic profiling of complex biological samples. Herein, we established an ion-pair reversed-phase×reversed-phase two-dimensional liquid chromatography (IPRP×RP 2DLC) strategy for comprehensive proteomic analysis. Both RPLC separation dimensions were performed at low pH, with trifluoroacetic acid(TFA) and formic acid(FA) as mobile phase addictive, respectively. As the good separation resolution offered by ion-pairing effect of TFA, the fractionation efficiency was greatly improved with 74.0% peptides identified in just one fraction. Comparing with conventional high pH RP fractionation, the overall separation rate of IPRP was about 1.6 times that of high-pH RP, which increased the number of identified peptides by 21%. Further, 2169 proteins and 8540 peptides were confidently identified from crude serum sample by our IPRP×RP 2DLC strategy, exhibiting great potential in clinical proteomics in the future.

The mechanism is investigated for Cp ^tBuRh(OH)₂-catalyzed annulation of 2-biphenylboronic acid with three activated alkenes using M06-2X functional. The reaction comprises transmetalation via two steps and following C-H activation producing reactive Rh-biphenyl complex with two Rh—C σ bonds. After the coordination/insertion of alkenes, respective fused or bridged cyclic products are yielded depending on different alkenes accompanied by the release of Cp ^tBuRh. The promotion of Cp ^tBuRh(OH)₂ lies in the barrier decrease of transmetalation and C-H activation ready for coordination/insertion ensuring the smooth progress of common rate-limiting reductive elimination. The stereoselective transfer and ring rotation are specific for benzoquinone and cyclopropenone. The role of Rh(III) catalyst and release of Rh(I) is supported by Multiwfn analysis on frontier molecular orbital(FMO) of specific transiton states(TSs) and Mayer bond order(MBO) value of vital bonding, breaking.

A novel hollow carbon derived from biomass lotus-root has been prepared by a one-step carbonization method. The carbon anode obtained at 900 °C showed the best electrochemical performance, corresponding to a high specific capacity of 445 mA·h/g at 0.1 C, as well as excellent cycling stability after 500 cycles. Further investigation exhibits that the lithium storage of hollow carbon involves Li⁺ adsorption in the defect sites and Li⁺ insertion. The results showed that the intrinsic structure of lotus root can inspire us to prepare biomass carbon with a hollow structure as an excellent anode for lithium-ion batteries.

Poly(lactic-co-glycolic acid)(PLGA) is one of the most representative degradable copolymers and promising drug carriers. In the current paper, the PLGAs with a lactic acid/glycolic acid(LA/GA) molar ratio of 52/48 and various molecular weights were prepared by a melting method. The molecular weight, molecular weight distribution, and thermal stability were determined by ¹H NMR and thermogravimetric analysis methods. The results demonstrated that PLGAs with the fixed LA/GA molar ratio(52/48), different molecular weights, and narrow molecular weight distribution could be obtained by solely altering the reaction time. The PLGA films were prepared, and their properties including micro-structure, mechanical property, in-vitro cytotoxicity, and biodegradability were characterized. In combination with the homogeneous microstructures and mechanical properties, the drug-loading and releasing properties of PLGA_3.2 films were investigated. The results show that PLGA_3.2 film with an LA/GA molar ratio of 52/48 is a promising curcumin carrier.

The enthalpies of formation of solid organic compounds containing carbon, nitrogen, oxygen, and hydrogen were estimated using two suggested descriptor sets, separately, by machine learning methods. The two descriptor sets are both composed of descriptors of Benson’s groups and corrected groups. The main differences between them are that one is generated based on atoms and the other is based on bonds. An in-house program was specially written in Java to extract all the descriptors with a function to ensure that each atom(or bond) of a molecule is represented by Benson’s groups once for an atom-based(or bond-based) descriptor set. Multiple linear regression and partial least squares were used, separately, to build models to predict the enthalpy of formation for two descriptor sets. The combination of the models constructed by two descriptor sets based on the atoms and the bonds achieved the best-predicted results in this paper, and the corresponding results of the test set are better than that in the literature, from which the original data were retrieved. Further, a small data set of fluorinated molecules was collected, and satisfactory results were also obtained for these molecules containing fluorine with the assistance of the former data set.

A luminescent Ag-based metal-organic framework(compound 1) has been synthesized and its structure has been characterized. Compound 1 was fabricated using the Ag+ and bbimb²⁻ ligands and manifestes a rare LON topology. Compound 1 is selective not only in detecting traces of Fe³⁺ and 2,4,6-trinitrophenol(TNP) via luminescence quenching, but also demonstrates high selectivity in the presence of other competitors. Compound 1’s K _sv values towards Fe³⁺ can reach as high as 9.3×l0³ L/mol, which is higher than those of several other MOF materials. It is also a recyclable luminous sensor with the potential to be utilized for detecting TNP. Hence, based on its characteristics, compound 1 can be regarded as a prospective luminescence sensor for detecting Fe³⁺ and TNP.

The adsorption method is considered to be one of the most promising organic pollutants emission reduction strategies. The design and synthesis of high-performance porous adsorbents are one of the most important but challenging works. In this work, we constructed a new class of porous molecular cage switches by a simple reaction using phenolphthalein as the raw material. The molecular cage switches displayed interesting on-off behavior towards organic guests, which is highly responding to organic pollutants with rapid color change and is also able to adsorb these organic pollutants through an open-to-close pathway. This molecular cage switch also has excellent regenerative cycling properties and water resistance, which is expected to be employed in the handling of organic pollutants in the future.

Iodized salts are widely used as mediators to promote C-H functionalization. Solvents and additives have been described as significant roles in these reactions. However, the further electrochemical investigations have rarely been reported. Herein, a KI mediated electrochemical annulation between acetophenones and 2-amniopyridines was developed. We revealed the effect of acids and solvents by cyclic voltammetry(CV), differential pulse voltammetry(DPV), and square wave voltammetry(SWV). The oxidation of 2-aminopyridine is inhibited at the potential window with the addition of strong acids, and the lowest oxidation potential difference of KI was obtained by utilizing EtOH as solvent. The experimental studies also show that the mixture solvent of EtOH/DMSO(9/1, volume ratio) facilitates the electrochemical cyclization due to the solubility improvement of KI. CF₃SO₃H has been screened as the optimal acid. A range of Imidazo[1,2-a]-pyridines have been synthesized in yields of 42% to 96%. Electrochemical investigations present that the KI mediated electrochemical reaction is probably solvent-dependence.