Formation and fluorescent mechanism of red emissive carbon dots from o-phenylenediamine and catechol system

Effect of quercetin on the protein-substrate interactions in SIRT6: Insight from MD simulations

SIRT6 is of interest for its promising effect in the treatment of aging-related diseases. Studies have shown quercetin (QUE) and its derivatives have varying degrees of effect on the catalytic effect of SIRT6. In the research, the effect of QUE on the protein-substrate interaction in the SIRT6-mediated mono-ADP ribosylation system was investigated by conventional molecular dynamics (MD) simulations combined with MM/PBSA binding free energy calculations. The results show that QUE can bind stably to SIRT6 with the binding energy of -22.8 kcal/mol and further affect the atomic interaction between SIRT6 and NAD+ (or H3K9), resulting in an increased affinity between SIRT6-NAD+ and decreased SIRT6-H3K9 binding capacity. At the same time, the binding of QUE can also alter some structural characteristics of the protein, with large shifts occurring in the residue regions involving the N-terminal (residues 1-27), Rossmann fold regions (residues 55-92), and ZBD (residues 164-179). Thus, QUE shows great potential as a scaffold for the design of novel potent SIRT6 modulators.

Rare-Earth-Metal-Free Solid-State Fluorescent Carbonized-Polymer Microspheres for Unclonable Anti-Counterfeit Whispering-Gallery Emissions from Red to Near-Infrared Wavelengths

Colloidal carbon dots (CDs) have garnered much attention as metal-free photoluminescent nanomaterials, yet creation of solid-state fluorescent (SSF) materials emitting in the deep red (DR) to near-infrared (NIR) range poses a significant challenge with practical implications. To address this challenge and to engineer photonic functionalities, a micro-resonator architecture is developed using carbonized polymer microspheres (CPMs), evolved from conventional colloidal nanodots. Gram-scale production of CPMs utilizes controlled microscopic phase separation facilitated by natural peptide cross-linking during hydrothermal processing. The resulting microstructure effectively suppresses aggregation-induced quenching (AIQ), enabling strong solid-state light emission. Both experimental and theoretical analysis support a role for extended π-conjugated polycyclic aromatic hydrocarbons (PAHs) trapped within these microstructures, which exhibit a progressive red shift in light absorption/emission toward the NIR range. Moreover, the highly spherical shape of CPMs endows them with innate photonic functionalities in combination with their intrinsic CD-based attributes. Harnessing their excitation wavelength-dependent photoluminescent (PL) property, a single CPM exhibits whispering-gallery modes (WGMs) that are emission-tunable from the DR to the NIR. This type of newly developed microresonator can serve as, for example, unclonable anti-counterfeiting labels. This innovative cross-cutting approach, combining photonics and chemistry, offers robust, bottom-up, built-in photonic functionality with diverse NIR applications.

Formation and Fluorescent Mechanism of Multiple Color Emissive Carbon Dots from o-Phenylenediamine

Carbon dots (CDs) have received considerable attention in many application areas owing to their unique optical properties and potential applications; however, the fluorescent mechanism is an obstacle to their applications. Herein, three-color emissive CDs are prepared from single o-phenylenediamine (oPD) by regulating the ratio of ethanol and dimethylformamide (DMF). Fluorescent mechanism of these CDs is proposed as molecular state fluorescence. Reaction intermediates are identified using liquid chromatrography-mass spectroscopy (LC-MS) and 1H nuclear magnetic resonance (NMR) spectra. 1H-Benzo[d]imidazole (BI), 2,3-diaminophenazine (DAP), and 5,14-dihydroquinoxalino[2,3-b] phenazine (DHQP) are proposed to be the fluorophores of blue, green, and red emissive CDs by comparing their optical properties. As per the LC-MS and 1H-NMR analysis, DHQP with red emission tends to form from DAP and oPD in pure ethanol. By adding DMF, BI formation is enhanced and DHQP formation is suppressed. The prepared CDs exhibit green emission with DAP. When the DMF amount is >50%, BI formation is considerably promoted, resulting in DAP formation being suppressed. BI with blue emission then turns into the fluorophore of CDs. This result provides us an improved understanding of the fluorescent mechanism of oPD-based CDs, which guides us in designing the structure and optical properties of CDs.

Carbon Dots-Inked Paper with Single/Two-Photon Excited Dual-Mode Thermochromic Afterglow for Advanced Dynamic Information Encryption

Achieving thermochromic afterglow (TCAG) in a single material for advanced information encryption remains a significant challenge. Herein, TCAG in carbon dots (CDs)-inked paper (CDs@Paper) is achieved by tuning the temperature-dependent dual-mode afterglow of room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF). The CDs are synthesized through thermal treatment of levofloxacin in melting boric acid with postpurification via dialysis. CDs@Paper exhibit both TCAG and excitation-dependent afterglow color properties. The TCAG of CDs@Paper exhibits dynamic color changes from blue at high temperatures to yellow at low temperatures by adjusting the proportion of the temperature-dependent TADF and phosphorescence. Notably, two-photon afterglow in CDs-based afterglow materials and time-dependent two-photon afterglow colors are achieved for the first time. Moreover, leveraging the opposite emission responses of phosphorescence and TADF to temperature, CDs@Paper demonstrate TCAG with temperature-sensing capabilities across a wide temperature range. Furthermore, a CDs@Paper-based 3D code containing color and temperature information is successfully developed for advanced dynamic information encryption.

Red Emitting Solid-State CDs/PVP with Hydrophobicity for Latent Fingerprint Detection

Fluorescent carbon dots (CDs) are a new type of photoluminescent nanomaterial. Solid-state CDs usually undergo fluorescence quenching due to direct π-π* interactions and superabundant energy resonance transfer. Therefore, the preparation of solid-state fluorescent CDs is a challenge, especially the preparation of long wavelength solid-state CDs. In this research, long wavelength emission CDs were successfully synthesized by solvothermal methods, and the prepared CDs showed good hydrophobicity. The composite solid-state CDs/PVP (Polyvinyl pyrrolidone) can emit strong red fluorescence, and the quantum yield (QY) of the CDs/PVP powder reaches 18.9%. The prepared CDs/PVP solid-state powder was successfully applied to latent fingerprint detection. The results indicate that the latent fingerprints developed by CDs/PVP powder have a fine definition and high contrast visualization effect, which proves that the prepared CDs/PVP has great application potential in latent fingerprint detection. This study may provide inspiration and ideas for the design of new hydrophobic CDs.

Carbon Dots: Synthesis, Characterizations, and Recent Advancements in Biomedical, Optoelectronics, Sensing, and Catalysis Applications

Carbon nanodots (CNDs), a fascinating carbon-based nanomaterial (typical size 2-10 nm) owing to their superior optical properties, high biocompatibility, and cell penetrability, have tremendous applications in different interdisciplinary fields. Here, in this Review, we first explore the superiority of CNDs over other nanomaterials in the biomedical, optoelectronics, analytical sensing, and photocatalysis domains. Beginning with synthesis, characterization, and purification techniques, we even address fundamental questions surrounding CNDs such as emission origin and excitation-dependent behavior. Then we explore recent advancements in their applications, focusing on biological/biomedical uses like specific organelle bioimaging, drug/gene delivery, biosensing, and photothermal therapy. In optoelectronics, we cover CND-based solar cells, perovskite solar cells, and their role in LEDs and WLEDs. Analytical sensing applications include the detection of metals, hazardous chemicals, and proteins. In catalysis, we examine roles in photocatalysis, CO2 reduction, water splitting, stereospecific synthesis, and pollutant degradation. With this Review, we intend to further spark interest in CNDs and CND-based composites by highlighting their many benefits across a wide range of applications.

Size Isn't Everything: Geometric Tuning in Polycyclic Aromatic Hydrocarbons and Its Implications for Carbon Nanodots

Recent developments in light-emitting carbon nanodots and molecular organic semiconductors have seen renewed interest in the properties of polycyclic aromatic hydrocarbons (PAHs) as a family. The networks of delocalized π electrons in sp2-hybridized carbon grant PAHs light-emissive properties right across the visible spectrum. However, the mechanistic understanding of their emission energy has been limited due to the ground state-focused methods of determination. This computational chemistry work, therefore, seeks to validate existing rules and elucidate new features and characteristics of PAHs that influence their emissions. Predictions based on (time-dependent) density functional theory account for the full 3-dimensional electronic structure of ground and excited states and reveal that twisting and near-degeneracies strongly influence emission spectra and may therefore be used to tune the color of PAHs and, hence, carbon nanodots. We particularly note that the influence of twisting goes beyond torsional destabilization of the ground-state and geometric relaxation of the excited state, with a third contribution associated with the electric transition dipole. Symmetries and peri-condensation may also have an effect, but this could not be statistically confirmed. In pursuing this goal, we demonstrate that with minimal changes to molecular size, the entire visible spectrum may be spanned by geometric modification alone; we have also provided a first estimate of emission energy for 35 molecules currently lacking published emission spectra as well as clear guidelines for when more sophisticated computational techniques are required to predict the properties of PAHs accurately.

o-phenylenediamine Derived Fluorescent Carbon Quantum dots for Detection of Hg(II) in Environmental Water

With the expansion of human activities, the consequent influx of mercury (Hg) into the food chain and the environment is seriously threatening human life. Herein, nitrogen and sulfur co-doped fluorescent carbon quantum dots (yCQDs) were prepared via a hydrothermal method using o-phenylenediamine (OPD) and taurine as precursors. The morphological characteristics as well as spectral features of yCQDs indicated that the photoluminescence mechanism should be the molecular state fluorophores of 2, 3-diaminophenothiazine (oxOPD), which is the oxide of OPD. The as-synthesized yCQDs exhibited sensitive recognition of Hg2+. According to the investigation in combination of UV-Vis absorption spectra, time-resolved fluorescence spectra and quantum chemical calculations, the abundant functional groups on the surface of yCQDs allowed Hg2+ to bind with yCQDs through various interactions, and the formed complexes significantly inhibited the absorption of excitation light, resulting in the static fluorescence quenching of yCQDs. The proposed yCQDs was utilized for Hg2+ sensing with the limit of detection calculated to be 4.50 × 10- 8 M. Furthermore, the recognition ability of yCQDs for Hg2+ was estimated in tap water, lake water and bottled water, and the results indicated that yCQDs have potential applications in monitoring Hg2+.

Transformation of crystal structure induced by the temperatures in carbon dots (CDs)-based composites with multicolor fluorescence for white Light-Emitting-Diode (WLED)

Regulation of the fluorescence through crystalizing from the matrix in the Carbon dots (CDs)-based solid-state materials has been verified to be one of the effective methods, yet there are not only challenges in preparing such materials efficiently, but also insufficient insight into their regulation mechanisms. Here, a one-pot solvothermal route to synthesize a series of CDs-based composites with crystalline matrix is reported. These crystals exhibited multicolor fluorescence with the feature of multi-peaks emissions with increasing temperatures from 140 ℃ to 220 ℃, in which the orange emitting O-CDs@PA and the yellow emitting Y-CDs@PA crystals obtained the FLQYs of 22% and 68% respectively due to relatively stable crystalline structures. After comparative analysis to both crystals in detail, the core and the groups associated with them on the interface between CDs and matrix were adjusted in size and species during structural transformation of the crystal matrix, which changes radically the energy band structures to influence fluorescent emitting of both crystals ultimately. In addition, the reasons resulting in higher FLQY for Y-CDs@PA were provided leveraging the schematic illustration presumed based on the PL properties of both crystals. Because of the optimal optical performances, these fluorescent materials promised to fabricate WLED devices and obtained a number of photometric parameters endowed these WLED devices with the feature of warm-white light.

Carbon Dots: From Synthesis to Unraveling the Fluorescence Mechanism

Carbon dots (CDs) being a new type of carbon-based nanomaterial have attracted intensive interest from researchers owing to their excellent biophysical properties. CDs are a class of fluorescent carbon nanomaterials that have emerged as a promising alternative to traditional quantum dots and organic dyes in applications including bioimaging, sensing, and optoelectronics. CDs possess unique optical properties, such as tunable emission, facile synthesis, and low toxicity, making them attractive for many applications in biology, medicine, and environmental areas. The synthesis of CDs is achievable by a variety of methods, including bottom-up and top-down approaches, involving the use of different carbon sources and surface functionalization strategies. However, understanding the fluorescence mechanism of CDs remains a challenge. Various mechanistic models have been proposed to explain their origin of luminescence. This review summarizes the recent developments in the synthesis and functionalization of CDs and provides an overview of the current understanding of the fluorescence mechanism.

Highly Antibacterial and Antioxidative Carbon Nanodots/Silk Fibroin Films for Fruit Preservation

The issues of fruit waste and safety resulting from rot have spurred a demand for improved packaging systems. Herein, we present highly antibacterial and antioxidative carbon nanodot/silk fibroin (CD/SF) films for fruit preservation. The films are composed of CDs and SF together with a small amount of glycerol via hydrogen bonding, exhibiting outstanding biosafety, transparency, and stretchability. The films effectively integrate key functionalities (atmosphere control, resistance to food-borne pathogens, and antioxidation properties) and can be manufactured in large sizes (about 20 × 30 cm), boasting a transmission rate of 13 183 cm3/m2·day for oxygen and 2860 g/m2·day for water vapor, favoring the preservation of fresh fruits. A convenient dip-coating method enables in situ fabrication of films with a thickness of approximately 14 μm directly on the fruits' surface providing comprehensive protection. Importantly, the films are washable and biodegradable. This work presents a promising technology to produce multifunctional and eco-friendly antibacterial packaging systems.

Photoluminescence of Argan-Waste-Derived Carbon Nanodots Embedded in Polymer Matrices

In this work, photoluminescent (PL) carbon nano dots (CNDs) prepared from argan waste were embedded in highly optical transparent poly(styrene-co-acrylonitrile) (PSA) and cyclo-olefin copolymer (COC) matrices, which were further processed into thin films. In the first step, the luminescent CNDs were prepared through thermal processing of fine-groundargan waste, followed, in the second step, by direct dispersion in the polymer solutions, obtained by solving PSA and COC in selected solvents. These two polymer matrices were selected due to their high optical transparency, resilience to various environmental factors, and ability to be processed as quality thin films. The structural configuration of the CNDs was investigated through EDX, XPS, and FTIR, while DLS, HR-SEM, and STEM were used for their morphology investigation. The luminescence of the prepared CNDs and resulted polymer nanocomposites was thoroughly investigated through steady-state, absolute PLQY, and lifetime fluorescence. The quality of the resulted CND-polymer nanocomposite thin films was evaluated through AFM. The prepared highly luminescent thin films with a PL conversion efficiency of 30% are intended to be applied as outer photonic conversion layers on solar PV cells for increasing their conversion efficiency through valorization of the UV component of the solar radiation.

Molecular Engineering of Highly Fluorinated Carbon Dots: Tailoring Li+ Dynamics and Interfacial Fluorination for Stable Solid Lithium Batteries

Fluorinated carbon dots (FCDs) have garnered interest owing to their distinct physicochemical properties. Nevertheless, intricate synthesis procedures and quite low fluorine doping levels limit its development and application. Herein, we propose a facile approach based on the Claisen-Schmidt reaction to realize gram-scale synthesis of highly fluorinated carbon dots (up to 20.79 at. %) at room temperature and atmospheric pressure, and a comprehensive exploration of the specific reaction mechanism is conducted. Furthermore, in consideration of the high fluorine content, good dispersibility, and compatibility with polymer electrolyte, the synthesized FCDs are utilized as an additive for PEO-based solid electrolytes of a Li battery to improve its ionic conductivity, interface stability, and mechanical properties. The introduction of FCDs can not only reduce the crystallinity of PEO and enhance the interaction of polymer chains, but also facilitate the establishment of uninterrupted pathways and in situ fluorination at the interface, which is substantiated by both theoretical calculations and experimental findings. As a result, the lithium symmetrical battery can operate stably for 1000 h at a current density of 0.4 mA cm-2. Simultaneously, the LiFePO4/Li battery utilizing the composite electrolyte exhibits a capacity of 130.3 mAh g-1 over 300 cycles while maintaining a capacity retention rate of 95.10%. This study develops a strategy for synthesizing highly fluorinated carbon dots, which demonstrate a useful influence on PEO electrolytes, thus boosting the advancement of FCDs and solid-state batteries.

Ultra-fast solvent-free protocol remodels the large-scale synthesis of carbon dots for nucleolus-targeting and white light-emitting diodes

Carbon dots (CDs) provides unprecedented opportunities for optical applications due its unique properties, but the energy-extensive consumption, high-risk factor and time-consuming synthesis procedure greatly hinders its industrialization process. Herein, we proposed an ultra-low energy consumption solvent-free synthetic strategy for fast preparing green/red fluorescence carbon dots (G-/R-CDs) using m-/o-phenylenediamine and primary amine hydrochloride. The involvement of primary amine hydrochloride can improve the formation rate of G-CDs/R-CDs through effectively absorbing microwave energy and providing acid react environment. The developed CDs exhibit good fluorescence efficiency, optical stability and membrane permeability for dexterous bioimaging in vivo. Based on inherently high nitrogen content, the G-CDs/R-CDs possess excellent nuclear/nucleolus targeting ability, and were successfully applied for screening cancer and normal cells. Furthermore, the G-CDs/R-CDs were further applied for fabricating high-safety and high-color rendering index white light-emitting diodes, providing a perfect candidate for indoor lighting. This study opens up new horizons for advancing practical applications of CDs in related fields of biology and optics.

Self-Precipitation of Highly Purified Red Emitting Carbon Dots as Red Phosphors

Colloidal carbon dots (C-dots) have attracted a great deal of attention for their unique optical properties. However, it is still a challenge to obtain highly purified C-dots without using multiple-step purification or postsize selection. In this work, a self-precipitation hydrothermal reaction was used to synthesize red-emitting C-dots (R-C-dots) using o-phenylenediamine (o-PDA) as a precursor without using any catalyst. The R-C-dots are able to precipitate on the wall of the reactor, which enables us to obtain solid-state C-dots with high purity. The R-C-dots have a photoluminescence quantum yield (PLQY) of as high as 36.75%, which is among the highest PLQY values reported previously for R-C-dots without using catalysts. The transient PL and transient absorption spectra revealed that 5,14-dihydroquinoxalino[2,3-b]phenazine linked on the surface of the C-dots determined the red luminescence behavior. This work provides a new path for the controllable synthesis of high-purity R-C-dots, showing potential applications in optoelectronic devices.

Highly fluorescent N, F co-doped carbon dots with tunable light emission for multicolor bio-labeling and antibacterial applications

Carbon dots (CDs) have emerged as potential biomaterials for bioimaging and antimicrobial applications. However, the lack of tunable long-wavelength emission performance and imprecise antibacterial mechanism limit their practical application. Thus, developing versatile CDs that combine outstanding optical performance and excellent antibacterial activity is of great practical significance. Herein, we prepared a novel nitrogen and fluorine co-doped CDs (N, F-CDs) from o-phenylenediamine and 2,3,5,6-tetrafluoroterephthalic acid, which exhibit high fluorescence quantum yield of 52.2%, large Stokes shift of 112 nm, as well tunable multicolor emission light from blue to red region. Thanks to the high biocompatibility and excellent photostability, the N, F-CDs were successfully implemented to multicolor biolabeling of mammalian cells, protozoan cells and plant cells. Moreover, the negatively charged N, F-CDs hold inherent efficient antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). By thoroughly studying the underlying antibacterial mechanisms at the molecular level through real-time quantitative PCR assay, we found the expression of related genes was notably down-regulated, further demonstrated that N, F-CDs against two bacterial strains had distinct target pathways. Our work provides a new reference for developing highly fluorescent multicolor CDs, and may facilitate the design and application of CDs-based nanomaterials in biological environment.

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.

Red emissive carbon dots: a promising next-generation material with intracellular applicability

The accidental discovery of carbon dots (CDs) back in 2004 has led to their widespread use in the biomedical field. CDs have demonstrated their effectiveness in reporting 3D structures of biological specimens, identifying normal and cancer cells, and even detecting analytes within cells. However, the limitations of blue-green emitting CDs, such as their shallow penetration, photodamage, and auto-fluorescence, have hindered their practical applications. To overcome these limitations, red emissive CDs (RCDs) have been developed, which have deep tissue penetration, minimal photo-damage, low auto-fluorescence, and high imaging contrast. In this article, we present a thorough review on the use of RCDs in biomedical applications, including in vivo and in vitro bioimaging, photoacoustic imaging, monitoring temperature and polarity changes in living cells, tumour therapy, and drug delivery. With the rapid progress being made in the development of RCDs for intracellular applications, their clinical application is expected to become a reality in the near future.

Effect of conjugation length on fluorescence characteristics of carbon dots

The influence of sp2- and sp3-hybridized carbon coexisting in carbon cores on fluorescence characteristics of carbon dots (CDs) was revealed by density functional theory calculations. Based on the constructed coronene-like structures, the fluorescence emission spectra, transition molecular orbital pairs and several physical quantities describing the distribution of electrons and holes were investigated. The results indicate that due to the interaction between sp2 and sp3 carbon atoms, two main factors including the hyperconjugative effect and the separation of sp2 domain by sp3 carbon atoms can regulate the fluorescence wavelength. By analyzing the transition molecular orbital pairs, it was found that the fluorescence wavelength has a close correlation with the conjugation length, suggesting that the conjugation length can predict the shift of the emission spectra of CDs. The theoretical results provide a comprehensive understanding of fluorescence mechanism and help to synthesize CDs with expected fluorescence wavelength.

Synthetic strategies, properties and sensing application of multicolor carbon dots: recent advances and future challenges

Recently, carbon dots (CDs) as newly developed carbon-based nanomaterials due to advantages such as excellent photostability and easy surface functionalization have generated wide application prospects in fields such as biological imaging and chemical sensing. The multicolor emission carbon dots (M-CDs) were acquired through the selection of different carbon source precursors, change of synthesis conditions and synthesis environment. Therefore, the aim of this review is to summarize the latest research progress in polychromatic CDs from the perspectives of synthesis strategies, luminescent mechanisms, luminescent properties and applications. This review focuses on how to prepare MCDs by changing raw materials and synthesis conditions such as reaction temperature, synthesis time, synthesis pH, and synthesis solvent. This review also presents the optical properties of MCDs, concentration effects, solvent effects, pH effects, elemental doping, and surface passivation on them, as well as their creative applications in the field of sensing applications. It is anticipated that this review will serve as a guide for the development of multifunctional M-CDs and inspire future research on controllable design and preparation of M-CDs.

Polymer-Derived Carbon Nanofiber and Its Photocurrent-Switching Responses of Carbon Nanofiber/Cu Nanocomposite in Wide Ranges of Excited Light Wavelength

Transformation into electric or photoelectric functional composite from non-conjugated polymers is a great challenge due to the presence of a large number of locative states. In this paper, carbon nanofiber was synthesized via hydrothermal carbonization utilizing carboxymethyl cellulose as a precursor, and the carbon nanofiber/Cu nanocomposite was constructed for defect passivation. The results indicated that the resulting nanocomposites exhibited good absorbance in visible light range and NIR (near-infrared). The photoconductive responses to typical weak visible light (650 nm et al.) and NIR (808, 980, and 1064 nm) were studied based on Au gap electrodes on flexible polymer substrates. The results exhibited that the nanocomposite's solid thick film showed photocurrent-switching behaviors to visible light and NIR, the switch-ratio was depending on the wavelengths and power of incident lights. The positive and negative photoconductance responses phenomenon was observed in different compositions and changing excited wavelengths. Their photophysical mechanisms were discussed. This illustrated that the nanocomposites easily produce free electrons and holes via low power of incident light. Free electrons and holes could be utilized for different purposes in multi-disciplinary fields. It would be a potential application in broadband flexible photodetectors, artificial vision, simulating retina, and bio-imaging from visible light to NIR. This is a low-cost and green approach to obtain nanocomposite exhibiting good photocurrent response from the visible range to NIR.

Synthesis of Multiple Emission Carbon Dots from Dihydroxybenzoic Acid via Decarboxylation Process

Carbon dots (CDs), as a new zero-dimensional carbon-based nanomaterial with desirable optical properties, exhibit great potential for many application fields. However, the preparation technique of multiple emission CDs with high yield is difficult and complex. Therefore, exploring the large-scale and straightforward synthesis of multicolor CDs from a simple carbon source is necessary. In this work, the solvent-free method prepares a series of multicolor emission CDs from dihydroxybenzoic acid (DHBA). The maximum emission wavelengths are 408, 445, 553, 580, and 610 nm, respectively, covering the visible light region. The 2,4- and 2,6-CDs possess the longer emission wavelength caused by the 2,4-, and 2,6-DHBA easily undergo decarboxylation to form the larger sp² domain graphitized structure. These CDs incorporated with g-C₃N₄ can significantly improve the photocatalytic water-splitting hydrogen production rate by extending the visible light absorption and enhancing the charge separation efficiency. The long-wavelength emission CDs can further enhance photocatalytic activity primarily by improving visible light absorption efficiency.

Ratiometric Fluorescent Detection of Ultrasound-Regulated ATP Release: An Ultrasound-Resistant Cu,N-Doped Carbon Nanosphere

Focused ultrasound, as a protocol of cancer therapy, might induce extracellular adenosine triphosphate (ATP) release, which could enhance cancer immunotherapy and be monitored as a therapeutic marker. To achieve an ATP-detecting probe resistant to ultrasound irradiation, we constructed a Cu/N-doped carbon nanosphere (CNS), which has two fluorescence (FL) emissions at 438 and 578 nm to detect ultrasound-regulated ATP release. The addition of ATP to Cu/N-doped CNS was conducted to recover the FL intensity at 438 nm, where ATP enhanced the FL intensity probably via intramolecular charge transfer (ICT) primarily and hydrogen-bond-induced emission (HBIE) secondarily. The ratiometric probe was sensitive to detect micro ATP (0.2-0.6 μM) with the limit of detection (LOD) of 0.068 μM. The detection of ultrasound-regulated ATP release by Cu,N-CNS/RhB showed that ATP release was enhanced by the long-pulsed ultrasound irradiation at 1.1 MHz (+37%, p < 0.01) and reduced by the short-pulsed ultrasound irradiation at 5 MHz (-78%, p < 0.001). Moreover, no significant difference in ATP release was detected between the control group and the dual-frequency ultrasound irradiation group (+4%). It is consistent with the results of ATP detection by the ATP-kit. Besides, all-ATP detection was developed to prove that the CNS had ultrasound-resistant properties, which means it could bear the irradiation of focused ultrasound in different patterns and detect all-ATP in real time. In the study, the ultrasound-resistant probe has the advantages of simple preparation, high specificity, low limit of detection, good biocompatibility, and cell imaging ability. It has great potential to act as a multifunctional ultrasound theranostic agent for simultaneous ultrasound therapy, ATP detection, and monitoring.

Formation and Band Gap Tuning Mechanism of Multicolor Emissive Carbon Dots from m-Hydroxybenzaldehyde

Reported in 2004, carbon dots (CDs) have been widely used in various fields due to their excellent optical properties. However, the mechanism of their fluorescence modulation is still a controversial issue, which also seriously affects the further development of carbon dots. In this paper, m-hydroxybenzaldehyde is used as a raw material to obtain multicolor luminescent CDs by pyrolysis under different reaction conditions, thereby revealing the forbidden band tuning and formation mechanism of CDs. Different acid-base conditions lead to different reaction paths of the precursors, forming molecular fluorophores with different conjugated structures, which aggregate to eventually form CDs and further enhance the photoluminescence of the system by inhibiting the movement of the fluorescent centers.

The Formation Process and Mechanism of Carbon Dots Prepared from Aromatic Compounds as Precursors: A Review

Fluorescent carbon dots are a novel type of nanomaterial. Due to their excellent optical properties, they have extensive application prospects in many fields. Studying the formation process and fluorescence mechanism of CDs will assist scientists in understanding the synthesis of CDs and guide more profound applications. Due to their conjugated structures, aromatic compounds have been continuously used to synthesize CDs, with emissions ranging from blue to NIR. There is a lack of a systematic summary of the formation process and fluorescence mechanism of aromatic precursors to form CDs. In this review, the formation process of CDs is first categorized into three main classes according to the precursor types of aromatic compounds: amines, phenols, and polycyclics. And then, the fluorescence mechanism of CDs synthesized from aromatic compounds is summarized. The challenges and prospects are proposed in the last section.