Emissive Materials Research Articles

Deciphering Design of Aggregation-Induced Emission Materials by Data Interpretation.

This work presents a novel methodology for elucidating the characteristics of aggregation-induced emission (AIE) systems through the application of data science techniques. A new set of chemical fingerprints specifically tailored to the photophysics of AIE systems is developed. The fingerprints are readily interpretable and have demonstrated promising efficacy in addressing influences related to the photophysics of organic light-emitting materials, achieving high accuracy and precision in the regression of emission transition energy (mean absolute error (MAE) ∼ 0.13eV) and the classification of optical features and excited state dynamics mechanisms (F1score ∼ 0.94). Furthermore, a conditional variational autoencoder and integrated gradient analysis are employed to examine the trained neural network model, thereby gaining insights into the relationship between the structural features encapsulated in the fingerprints and the macroscopic photophysical properties. This methodology promotes a more profound and thorough comprehension of the characteristics of AIE and guides the development strategies for AIE systems. It offers a solid and overarching framework for the theoretical analysis involved in the design of AIE-generating compounds and elucidates the optical phenomena associated with thesecompounds.

Excited State Dynamics of Geometrical Evolution of α-Substituted Dibenzoylmethanatoboron Difluoride Complex with Aggregation-Induced Emission Property.

Organic molecules with an aggregation-induced emission (AIE) property have been attracting much attention from the viewpoint of application to solid state emissive materials. For the AIE mechanism, quantum mechanical studies proposed the restriction of the intramolecular motion (RIM) model with the contribution of the conical intersection (CI) and deduced the importance of the restricted access to a conical intersection (RACI) in the potential energy surface (PES). Although these theoretical studies have contributed to the elucidation of AIE phenomena, direct detection of the reaction dynamics is indispensable to clarify the actual PES and the deactivation mechanism. Along this line, we investigated excited state dynamics of the AIE molecule with dibenzoylmethanatoboron difluoride complexes using time-resolved absorption spectroscopies in both visible and infrared (IR) regions. While the reference system of 1,3-bis(4-methoxyphenyl)methanatoboron difluoride (2aBF2) showed strong emission in solution, the methyl-substituted derivative at the α-position of the dioxaborine ring (2amBF2) led to the very weak fluorescence in solution but strong emission in the solid state. Time-resolved visible absorption measurements revealed a peak shift and broadening of the stimulated emission in the solution of 2amBF2, owing to the rapid change of the molecular geometry. With the temporal evolution of time-resolved IR absorption signals and density functional theory (DFT) calculation of these systems, it was deduced that 2amBF2 has two stable geometries, namely, planar and bending, in the S1 state and the bending geometry in the S1 state led to rapid conversion to the S0 state. These results support the RACI model in the aggregated states, leading to the AIE properties.

Sustainable production of BioAIE materials from biomass

The research of aggregation‐induced emission (AIE) materials has aroused extensive interests during the past 20 years. Until recently, biomass‐inspired AIE (BioAIE) materials have become highly attractive owing to the advantages of natural structural diversity, renewability, biocompatibility, and biodegradability of the biomass. In this concept, we focus on the sustainable production of BioAIE materials from biomass resources (biomacromolecules and small natural products) through extraction, chemical conversion, and physical conversion. Chemical conversion is especially stated, including catalytic conversion, Schiff base reaction, “in water” reaction, and other chemical modifications. The luminescence mechanism of AIE behaviors along with their structure‐property relationships is emphasized, and the applications are addressed as well. An outlook is provided to highlight the challenges and opportunities associated with the future development trend in this field.

Deep‐red Emitting Copper(I) Indenediyltrisphosphine Complexes with Minimized Skeletal Vibrations and Configurational Disorder

Abstract: The full width at half maximum (FWHM) of emission spectra, which plays an important role in determining color purity, may not always receive sufficient attention in the design of emissive materials. Particularly for the red emitter, the traditional focus has been on emission maxima, yet broad FWHM values can significantly change the perceived color. For example, the red color (lem = 616–677 nm) emitted from reported Cu(I) complexes is perceived as orange to yellow if FWHM is large. To reduce FWHM, we incorporated a strained and rigid metalaphosphadicyclopenta[a,f]pentalene motif into Cu(I) complexes using trisphosphine ligands featuring a 1H‐indene‐2,3‐diyl backbone (ITP). Herein, we present the synthesis, structure, and emission properties of ITP‐MX and the congeners, showcasing genuinely deep‐red emission with narrow FWHM values of 56 nm. These materials exhibit color coordinates close to pure red on the CIE diagram, unlike reported broader‐emitting counterparts. Measurement of the entropy of disorder of the emissive crystal by a recently reported statistical mechanical method revealed a quantitative correlation between FWHM and the increase in the number of microstates (the degree of freedom) of the crystals and suggested that mechanical stress can increase the entropy of the crystal, which results in emission broadening.

Organic Room Temperature Phosphorescence from BN-Substituted Xanthene Derivatives.

Emissive organic materials are predominantly fluorescent and there is significant interest in realizing and understanding examples that defy this paradigm and exhibit phosphorescence under ambient conditions. Organic room temperature phosphorescence (ORTP) offers the long-lived excited states and bathochromically-shifted emission maxima of phosphorescence without the use of potentially toxic and expensive transition metals. Most ORTP materials rely on well-studied structural motifs that include aryl carbonyls, sulfones, and heavy main group elements. We report the unexpected ORTP of a series of heavy atom-free BN-substituted xanthene derivatives. The creation of heteroatom-rich scaffolds, combined with stabilizing C-H···F interactions in the solid-state, resulted in oxygen-tolerant heavy atom-free organic phosphorescence without relying on the use of cryogenic temperatures, polymer matrices, or host-guest interactions. The observation of ORTP in these simple systems sets a blueprint for the further development of heavy atom-free organic phosphors.

NiFe Nanoalloy Electrocatalyst as a Coreaction Accelerator for Enhancing Biomarker Electrochemiluminescence Imaging Detection.

The development of coreaction accelerators with excellent performance is crucial for improving electrochemiluminescence (ECL) performance. In this study, a NiFe nanoalloy electrocatalyst (NiFe-NAEC) was used as a coreaction accelerator to promote persulfate activation, resulting in a 44-fold increase in the ECL intensity of flower-like Zn-3,4,9,10-perylenetetracarboxylate (FL-Zn-PTC). Moreover, the synergistic combination of NiFe-NAEC and silver nanoparticles led to a 134-fold increase in the ECL intensity of FL-Zn-PTC, with a 6275% improvement in the ECL efficiency compared with a reference system containing Ru-bpy/K2S2O8. Consequently, a sensor was constructed for the visual detection of amino-terminal pro-brain natriuretic peptide. This sensor exhibited high sensitivity and provided intuitive results within a linear range from 0.01 to 1000 pg/mL, with a detection limit of 2.1 fg/mL. Overall, this study presents a strategy that integrates an electrocatalytic coreaction accelerator with synergistic enhancement to improve ECL performance. This approach has the potential to expand the range of emitter materials and advance ECL technology.

Anodization-Processed Colored Radiative Thermoregulatory Film.

Colored radiative thermal management materials (RTMM) not only provide superior thermoregulatory performance but also satisfy aesthetic requirements. However, the complexity of the preparation procedures and constrained color selection have hindered their widespread adoption. Here, we presented a facile one-step anodizing strategy for fabricating colored dual-mode RTMM based on titanium film (Ti) and P(VDF-HFP) with mid-infrared (MIR) emissivities of 0.07 and 0.96, respectively, which allow for on-demand temperature modulation (rise of 28.2 K and drop of 9 K) without energy consumption. Furthermore, demonstrations of a colored radiative warming membrane also validate the effectiveness of anodizing treatment. The colored Ti/nano PE membrane with 10.8 μm thickness enables a temperature rise of 2.3 K on real human skin, which is much higher than that of commercial fabric with 120 μm thickness (0.7 K). This strategy provides insights for the scalable fabrication and application of colored low emissivity materials, contributing to the goal of a sustainable society.

Advancing source apportionment of soil potentially toxic elements using a hybrid model: a case study in urban parks, Beijing, China.

Identifying the source-specific health risks of potentially toxic elements (PTE) in urban park soils is essential for human health protection. However, previous studies have mostly focused on the deterministic source-specific health risks, ignoring the health risk assessment from a probabilistic perspective. To fill this gap, we developed a hybrid model that incorporated machine learning (ML) interpretability into positive matrix factorization (PMF) and probability health risk assessment (PHRA) based on the Monte Carlo simulation. The results indicated that concentrations of soil PTEs except for Mn and Sb were significantly higher than their corresponding background values. Random forest (RF) was regarded as the best ML model to identify key drivers for As, Cd, Cr, Cu, Ni, Pb, and Zn, with R2 > 0.60, but was less effective for other soil PTEs (R2 < 0.49). Specifically, the contributions of the four potential pollutionsources were mixed sources, traffic emission, fuel combustion, and building materials, with contribution rate of 24.88%, 30.56%, 28.99%, and 15.56%, respectively. Fuel combustion contributed the most to non-carcinogenic for children (39.45%), male (43.84%), and female (43.76%), and the non-carcinogenic risk could be considered negligiblefor human. However, building materials was the major contributor to carcinogenic risk for children (36.1%), male (44.9%), and female (43.2%). The integration of the RF model with PMF and PHRA improved the accuracy of the results by identifying and quantifying the specific sources of each soil PTE using the relative importance analysis from the RF model. The results of this study assisted in providing efficient strategies for risk management and control of soil PTEs in Beijing parks.

Near‐Infrared‐Emitting Helically Twisted Conjugated Frameworks Consisting of Alternant Donor‐π‐Acceptor Units and Multiple Boron Atoms

AbstractA novel design strategy to construct bright and narrow near‐infrared (NIR) emission materials with suppressed shoulder peaks can significantly enhance their performance in various applications. Herein, we have successfully synthesized a series of helically twisted D‐π‐A conjugated systems bridged by boron atoms, achieving bright red to near‐infrared (NIR) emissions with notably narrow full‐width at half‐maximum (FWHM) values of 35 nm (0.08 eV) and photoluminescence quantum yields (PLQY) up to 80 %. These compounds display red‐shifted emissions up to 753 nm in higher concentrations. Cis/trans configurational isomers of multi‐boron‐bridged molecule BN3 exhibit similar photophysical properties. The unique combination of boron‐induced coordination‐enhanced charge transfer (CE‐CT) and the helically twisted conjugated framework is pivotal in achieving the red‐shifted, narrowband emission. X‐ray crystallographic analysis of BN2 and BN3‐a reveals that the extension of boron‐bridged D‐π‐A skeletons significantly increases the distortion of the skeleton. Systematic theoretical calculations show how the boron CE‐CT mechanism, in conjunction with the helical twist, leads to the narrowing of emission bands while simultaneously red‐shifting them into the NIR region. This work could open new avenues for the development of advanced materials with tailored optical properties, particularly in the challenging and highly sought‐after NIR spectrum.

A two-dimensional thin film structure with spectral selective emission capability suitable for high-temperature environments

Spectral selective emission materials, characterized by their high emission efficiency within specific wavelength ranges, play a crucial role in various fields such as infrared stealth and radiative cooling. In this study, leveraging the tunneling effect of ultrathin metal layers and the impedance matching principle, we designed a one-dimensional multilayer thin film structure composed of Mo/Ge/Al. This design successfully achieved spectral selective emission within the 3-14 μm infrared spectrum range, showcasing superior high-temperature infrared stealth capabilities. Research findings indicate that the infrared atmospheric window (ε3-5 μm=0.40, ε8-14 μm=0.30) maintains a low emissivity within the temperature range from room temperature to 400°C, while high emissivity in non-infrared atmospheric windows (ε5-8 μm=0.81) enables radiative cooling. The use of high emissivity in the non-infrared atmospheric window reduced the surface temperature of this structure by 15.3°C compared to untreated Si substrate under similar heating conditions. The temperature reduction was 34.1°C when compared to a Si substrate coated with a 200 nm Al film. This straightforward and easily scalable structure not only presents novel solutions for applications in infrared stealth and radiative cooling but also holds vast potential for diverse fields including military, aerospace, and industrial manufacturing, injecting fresh impetus and possibilities into technological advancement.

Luminescence Thermochromism of a Noncluster Copper Iodide Complex.

Hybrid copper(I) halide materials are currently attracting significant attention due to their exceptional luminescence properties, offering great potential for the development of multifunctional emissive materials with, in addition, eco-friendly features. A binuclear copper iodide complex, based on the [Cu2I2L4] motif with phosphite derivatives as ligands, has been synthesized and structurally characterized. Photophysical investigations indicate that this complex displays luminescence thermochromic properties, which are characterized by a temperature-dependent change in the relative intensity of two emission bands. The high-contrast luminescence thermochromism, with an important color variation from purple to cyan, is ascribed to the thermal equilibrium of two different excited states. While thermochromism is relatively known for multimetallic complexes, the perfectly controlled thermochromism of the studied compound is unprecedented for a binuclear complex. From theoretical investigations, this original feature is due to the coordination of phosphite ligands, which induces a specific energy layout of the complex, presenting vacant orbitals of varying nature. This single-component, dual-emissive binuclear complex, displaying relevant sensitivity temperature response, presents great potential for luminescence ratiometric thermometry applications. This study underlines the relevance of the ligand engineering strategy in developing original, emissive, and sustainable copper-based materials.

High contrast stimuli-responsive fluorescence emitters based on carbazole-cyanostilbene derivatives with aggregation induced emission properties

Due to the aggregation induced emission (AIE) materials exhibiting obvious fluorescent emission changes under the external stimuli of heat, solvent, force and so on, significant efforts have been directed toward developing AIE-active materials with high contrast stimuli-responsive fluorescence behaviors. Herein, three electron-donor(D)-electron-acceptor(A) and D-A-D type organic fluorescence emitters of Cz-DC-tBu, Cz-DC-CN and Cz-DC-OMe were facilely synthesized using carbazole group as D unit and cyano group as A unit. They showed typical AIE features and exhibited remarkable color changes under mechanical force and in different polarity solvents, respectively. The stimuli-responsive mechanism of the compounds were investigated by powder X-ray Diffraction (PXRD) and density functional theory calculations (DFT), which revealed that the mechanofluorochromic behaviors were associated with the molecular packing modes, and the solvatochromic effects were caused by the intramolecular charge-transfer transition (ICT) effect. Significantly, it was found that Cz-DC-tBu showed high contrast stimuli-responsive behaviors through adjusting the substituent groups on the cyanostilbene unit with CN, OMe, and tBu groups, respectively. This study provided a new strategy for the design of AIE-active stimuli-responsive fluorescence emitters, and made them possible using in stress sensors, chemical detection, memory storage, anti-counterfeiting applications.

Mono-/multi-fluorination of 1,8-naphthalimides for developing AIE/AIEE fluorophores with tuning emission wavelength

Aggregation-induced emission/aggregation-induced emission enhancement (AIE/AIEE) luminogens provides amount of highly emissive materials in density states for versatile applications. Most of the AIE/AIEEgens were designed with the multiply rotation unit, in which the additional rotation units not only extend the molecular structure but also suffer from low atom economy. Herein, a fluorination strategy was introduced to construct ten AIE/AIEEgens with 1∼3 fluorine (F) atoms at different position of phenyl ring at previous developed AIEgen, 4-phenyl-1,8-naphthalimide, which can output tuning emissive wavelength and high quantum yields in both aqueous solutions and solids. In these compounds, five AIEgens with ortho-F atom and five AIEEgens without ortho-F atom were obtained. All compounds show bright blue emissions centered at 430–485 nm in aqueous solutions and wide emissions covering visible region in solid states. We calculated the ratio of quantum yields between their aqueous solution and THF solution (Φwater/ΦTHF). The AIE luminogens show the higher ratios between 10.19 and 24.89 and the AIEEgens show the lower ratios between 1.89 and 6.40. This strategy based on changing the substituent positions of F atoms provides an efficient and convenient method for construction of novel AIE-active materials with variable photophysical properties in density states.

In situ Cyclization of Aromatic Thioethers in Emissive Materials to Generate Phosphorescent Dibenzothiophenes

AbstractIn this contribution, we explored the photocyclization of thioethers to highly substituted dibenzothiophenes (DBT) using solely UV‐light without any need for additives. This cost‐effective, robust and environmentally friendly approach yielded phosphorescent compounds, which were characterized by X‐ray crystallography and state‐of‐the‐art photophysical methods. The resulting DBTs feature ultralong photoluminescence lifetimes and quantum yields close to unity in frozen glassy matrices. The reaction mechanism was elucidated in detail through a combination of quantum chemical calculations and experimental results, providing evidence that triplet states are involved in the cyclization process. Additionally, the photoreaction can also be induced within materials. For this purpose, the precursors were integrated into polymer films or polymer resins suitable for 3D printing. Irradiation of these polymeric objects allows motifs with ultralong phosphorescence to be irreversibly inscribed through the proceeding photocyclization. The in situ photogeneration of DBTs from aromatic thioethers overcomes the observed incompatibilities regarding solubility in polymer resins for 3D printing.

In situ Cyclization of Aromatic Thioethers in Emissive Materials to Generate Phosphorescent Dibenzothiophenes.

In this contribution, we explored the photocyclization of thioethers to highly substituted dibenzothiophenes (DBT) using solely UV-light without any need for additives. This cost-effective, robust and environmentally friendly approach yielded phosphorescent compounds, which were characterized by X-ray crystallography and state-of-the-art photophysical methods. The resulting DBTs feature ultralong photoluminescence lifetimes and quantum yields close to unity in frozen glassy matrices. The reaction mechanism was elucidated in detail through a combination of quantum chemical calculations and experimental results, providing evidence that triplet states are involved in the cyclization process. Additionally, the photoreaction can also be induced within materials. For this purpose, the precursors were integrated into polymer films or polymer resins suitable for 3D printing. Irradiation of these polymeric objects allows motifs with ultralong phosphorescence to be irreversibly inscribed through the proceeding photocyclization. The in situ photogeneration of DBTs from aromatic thioethers overcomes the observed incompatibilities regarding solubility in polymer resins for 3D printing.

Benchmarking luminescent properties of the arylvinylpyrimidine scaffold.

The exploration of the photophysical properties of push-pull molecules incorporating pyrimidine rings as electron-attracting moieties in their structure continues to be a fascinating area of investigation. A thorough examination of these properties not only contributes to fundamental knowledge but also provides crucial insights for the rational design of emissive materials in prospective applications. In this context, this work conducts an in-depth analysis of four families of 4,6-bis(arylvinyl)pyrimidines, evaluating the influence of substituents on both the aryl groups and position 2 of the pyrimidine ring. While previous research has primarily focused on solution studies, this work emphasizes the importance of examining solid-state photophysics. Through a multidisciplinary approach encompassing optical techniques, x-ray diffraction, and quantum chemical calculations, a comprehensive understanding of the structure-property relationships is achieved. This study underscores the intricate interplay between molecular structure, aggregation, and fluorescence behavior in pyrimidines, offering valuable insights with broader implications beyond academic realms.

Coumarin-Based ACQ-AIE Conversion Photosensitizer for Mitochondrial Imaging and Synergistic Cancer Therapy.

Most of the traditional fluorescent molecules have the advantages of high fluorescence quantum yield, good stability, and excellent structural adjustability, but they exhibit the characteristics of fluorescence quenching caused by aggregation, which restricts their application in aqueous solutions or solids. The excellent luminescence properties and photosensitive potential of aggregation-induced emission (AIE) materials in a condensed state have made them widely concerned in the scientific research field, so it is very challenging to regulate the transformation of traditional aggregation-caused quenching (ACQ) fluorophores into AIE fluorophores. In this study, the traditional coumarin fluorophore was used as a matrix. After conjugating the triphenylamine AIE group, the triphenylphosphine cation was linked through the alkyl chain to obtain a molecular probe NCTPP with excellent AIE characteristic, water solubility, mitochondrial green light imaging, chemotherapy and photodynamic therapy capabilities. As far as we know, it was the first time that the photosensitivity of coumarin fluorescent molecules was imparted by the ACQ-AIE conversion method.

Inflated electronic and optical assessment of gC3N4/ZnO nanocomposite as a potential emissive layer material for OLED application

Organo-inorganic nanocomposite materials have been proven to be novel hybrid materials with inflated electronic and optical performance that can be tailored with the judicious selection of the building units or their combinations. Here, hydrothermal, thermal polycondensation, and ultrasonication techniques were used to synthesize pure ZnO, gC3N4, and gC3N4/ZnO with varying weights % such as 10 %, 15 %, 20 %, and 25 % of ZnO inorganic filler elements in gC3N4 matrix. The crystalline phase (hexagonal wurtzite) and crystallite size (10.0 nm, 17.6 nm, and 15.90 nm) of the synthesized materials were examined by X-ray diffractometer. The FESEM and HRTEM characterizations revealed the sheet-like gC3N4 and spherical-type ZnO nanoparticle-like microstructures of the samples. The present functional groups, corresponding vibrational frequency, chemical states, and binding energy were investigated using FTIR and XPS spectroscopic methods. Optical parameters such as optical band gap energy (Eg = 3.24 eV), Urbach energy (Eu = 0.41 eV), refractive index (n = 1.99), emission quantum yield (∼ 69.03 %), and color purity of the nanocomposites were examined using UV visible and photoluminescence spectroscopic techniques. IV and Hall measurements techniques were used to determine the semiconducting parameters of the optimized sample, such as conductivity (∼62.90×10−5 S/cm), carrier mobility (∼ 44.1 cm2/Volt. Sce), carrier concentrations (∼1.825×1014 cm−3), and sheet resistance (∼1.062×103 Ω/cm2). Due to their excellent optical and electrical behavior, the nanocomposite materials were found to be fairly suitable as a potential emissive layer material for OLED applications.

Oxygen‐doped Carbon Nitrides with Visible Room‐temperature Phosphorescence and Invisible Thermal‐Stimuli‐Responsive Ultraviolet Delayed Fluorescence for Security Applications

AbstractMulti‐mode emissive materials with stimuli‐responsive producing invisible signals are very attractive for advanced security applications, but development of such materials remains highly challenging. In this work, oxygen‐doped carbon nitrides (O‐CNs) are prepared via microwave‐assisted heating of urea, which exhibit ultraviolet (UV) solid‐state fluorescence (SSFL), visible room temperature phosphorescence (RTP) and thermal‐stimuli production of invisible UV delayed fluorescence (DF) properties. Further studies confirmed that the SSFL and RTP could be attributed to the introduction of oxygen functional group (e. g., C=O) in the skeleton of O‐CNs, thus minimizing the aggregation caused quenching effect, facilitating intersystem crossing, and stabilizing the excited triplet states. The specific thermal‐stimuli production of UV DF is deemed to be the relatively large energy gap between ground and excited singlet states as well as an effective triplet‐triplet annihilation. Notably, the emission maximum of UV DF locates at ~310 nm with an ultra‐narrow full width at half maximum (FWHM) down to 19 nm, so it is completely invisible to the naked eyes, but detectable by a UV camera. To employ the unique characteristics of O‐CNs, security protection strategies with superior concealment by virtue of the thermal‐stimuli quenching visible RTP and meanwhile producing invisible UV DF are demonstrated.

Oxygen-doped Carbon Nitrides with Visible Room-temperature Phosphorescence and Invisible Thermal-Stimuli-Responsive Ultraviolet Delayed Fluorescence for Security Applications.

Multi-mode emissive materials with stimuli-responsive producing invisible signals are very attractive for advanced security applications, but development of such materials remains highly challenging. In this work, oxygen-doped carbon nitrides (O-CNs) are prepared via microwave-assisted heating of urea, which exhibit ultraviolet (UV) solid-state fluorescence (SSFL), visible room temperature phosphorescence (RTP) and thermal-stimuli production of invisible UV delayed fluorescence (DF) properties. Further studies confirmed that the SSFL and RTP could be attributed to the introduction of oxygen functional group (e. g., C=O) in the skeleton of O-CNs, thus minimizing the aggregation caused quenching effect, facilitating intersystem crossing, and stabilizing the excited triplet states. The specific thermal-stimuli production of UV DF is deemed to be the relatively large energy gap between ground and excited singlet states as well as an effective triplet-triplet annihilation. Notably, the emission maximum of UV DF locates at ~310 nm with an ultra-narrow full width at half maximum (FWHM) down to 19 nm, so it is completely invisible to the naked eyes, but detectable by a UV camera. To employ the unique characteristics of O-CNs, security protection strategies with superior concealment by virtue of the thermal-stimuli quenching visible RTP and meanwhile producing invisible UV DF are demonstrated.