Achieving thermal-stimulus-responsive dynamic afterglow from carbon dots by singlet-triplet energy gap engineering through covalent fixation

The first carbon dot (CD)-based organic long persistent luminescence (OLPL) system exhibiting more than 1 h of duration was developed. In contrast to the established OLPL systems, herein, the reported CDs-based system (named m-CDs@CA) can be facilely and effectively fabricated using a household microwave oven, and more impressively, its LPL can be observed under ambient conditions and even in aqueous media. XRD and TEM characterizations, afterglow decay, time-resolved spectroscopy, and ESR analysis were performed, showing the successful composition of CDs and CA, the formation of exciplexes and long-lived charged-separated states. Further studies suggest that the production of covalent bonds between CA and CDs plays pivotal roles in activating LPL and preventing its quenching from oxygen and water. To the best of our knowledge, this is a very rare example of an OLPL system that exhibits hour-level afterglow under ambient conditions. Finally, applications of m-CDs@CA in glow-in-the-dark paints for emergency signs and multicolored luminous pearls were preliminarily demonstrated. This work may provide new insights for the development of rare-earth-free and robust OLPL materials.

Color-tunable and high-quantum-yield afterglow of carbon dots by covalent fixation

Heteroatoms-doped carbon dots: Fundamental, properties, coordination bonding and corrosion protection

Electrochemical synthesis of multicolor carbon dots with room temperature phosphorescence to thermally activated delayed fluorescence via surface state modulation

Spirulina-derived carbon dots with narrow-peak NIR emission for LED applications.

Carbon dots (CDs) have gained enormous attention in the class of carbon-based nanomaterials due to their outstanding features, including ultra-small size, hydrophilic nature, low cytotoxicity, and fluorescence, which makes them appropriate for various biomedical applications. Doping of heteroatoms in CDs improves their physicochemical properties, photophysical properties, and quantum yield by their regulatory size, morphology, structure, and energy gap. Doping with metal ions, especially transition metal ions, looks more predominate due to more number of electrons and unoccupied orbitals which make to alter the charge density on the surface of CDs. Furthermore, doping with lanthanide elements provides near-infrared (NIR) response and magnetic activity which are beneficial for NIR-responsive synergistic chemophototherapy and multimodal imaging-guided. Thus, herein we try to provide complete information of metal-doped CDs about their synthetic methods and application in imaging and cancer therapy. At first various synthetic methods for metallic ion doped CDs along with the effects of the reaction parameters and doping on the structure and properties of CDs were discussed. Further, we have broadly explained their applications as bioimaging agents and in the field of cancer phototherapy. Finally, this book chapter will give a promising understanding of various synthesis methods of metal-doped CDs and their biomedical application in both in vitro and in vivo.

Mechanistic regulation of gram-scale synthesis of triple emission cyanobacteria-based carbon dots and visual ratiometric sensing applications

Tunable multicolor carbon dots (CDs) with a quantum yield reach up to 35% were generated directly from rhodamine and urea via one-step hydrothermal approach and purified through silica gel column chromatography. Transmission electron microscopy images reveal that the as-prepared CDs possess a small size distribution below 10nm with bright blue, green, and yellow color emission, designated as b-CDs, g-CDs, and y-CDs, respectively. The in-depth investigations reveal that the multicolor emission CDs with different fraction displays fluorescence emission wavelength ranges from 398nm (b-CDs), 525nm (g-CDs), to 553nm (y-CDs) which could be well modulated by controlling the amount of heteroatom nitrogen especially amino nitrogen onto their surface structures. Further experiments verify the important role of nitrogen content by using rhodamine solely or substituting urea with sulfur containing compounds as precursors to produce corresponding CDs since the performance is lower than that of urea incorporation. Theoretical calculation results also reveal that the increasing amount of amino nitrogen into their surface structures of b-CDs, g-CDs to y-CDs is responsible for reduced band gaps energy, which result in the redshifted wavelength. Benefiting from the excellent photoluminescence properties, wide pH variation range, high photo stability, and low toxicity, these CDs were employed for HClO sensing at 553nm within the range 5 to 140μM with a limit of detection (LOD) of 0.27 ± 0.025μM (n = 3) and multicolor cellular imaging in HeLa cells. Tunable multicolor carbon dots (CDs) were generated directly from rhodamine and urea via one-step hydrothermal approach and purified through silica gel column chromatography. The as-prepared CDs exhibit bright blue, green, and yellow color emission which could be well modulated by controlling the increasing incorporation of heteroatom nitrogen especially amino nitrogen into their surface structures. These CDs were employed for HClO sensing and demonstrated to multicolor cellular imaging in HeLa cells.

Synthesis of novel carbon dots from taurine for Cu2+ sensing and nanohybrid with ceria for visible light photocatalysis

The confined synthesis of carbon dots (CDs) in solid matrixes is a promising avenue for developing new afterglow materials. Benefiting from the advantages of the sol-gel preparation of nanoporous glass, we report transparent glass-confined CDs with tunable afterglow luminescence. Switchable thermally-activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) of CDs were achieved by adjusting the sintering temperature and ion doping. Our findings reveal that with an increase in sintering temperature from 500 °C to 600 °C, the energy gap (ΔEST) of CD-nanoporous glass (NG) increased from 0.05 eV to 0.21 eV, while the lifetime increased from 329 ms to 548 ms, which is attributed to the enhanced carbonization degree of the CDs. Pb2+ doping is also shown to achieve switchable TADF and RTP of glass-confined CDs attributed to the alteration of interfacial interactions between the glass and confined CDs. This design concept introduces a new perspective for developing transparent afterglow materials for various unique phosphorescence applications.

Carbon dot (CD)-based room temperature phosphorescent (RTP) materials exhibit significant potential for advanced optical applications, including information encryption and anticounterfeiting. However, the rational surface engineering of CDs through the incorporation of light-metal ions to achieve an RTP emission remains a formidable challenge. Herein, we present a microwave-assisted aluminum coordination strategy that facilitates the surface polymerization of phosphorus-doped CDs, thereby achieving enhanced green RTP emission in Al3+-cross-linked CDs (Al-CDs) with a lifetime from 172 to 782 ms. The photophysical and structural characterizations reveal that aluminum ions coordinate with CDs, forming a cross-linked polymerized structure that effectively enhances the intersystem crossing (ISC) process, avoids aggregation-induced quenching, and suppresses nonradiative transitions. The other light-metal ions (Ca2+ and Na+) could also be coordinated with CDs through this microwave-assisted strategy, while Al-CDs exhibit better RTP properties due to the smaller energy gap between the singlet and triplet states (ΔEST). The mechanism of the enhanced RTP emission in the light-metal surface polymerization of CDs was further validated through systematic calculations. Due to its long-lived RTP emission and simple synthesis process, Al-CDs exhibit significant potential in the fields of information encryption and anticounterfeiting.

In this work, we present the fabrication of highly luminescent carbon dots (CDs) by a double passivation method with the assistance of Ca(OH)2. In the reaction process, Ca2+ protects the active functional groups from overconsumption during dehydration and carbonization, and the electron-withdrawing groups on the CD surface are converted to electron-donating groups by the hydroxyl ions. As a result, the fluorescence quantum yield of the CDs was found to increase with increasing Ca(OH)2 content in the reaction process. A blue-shift optical spectrum of the CDs was also found with increasing Ca(OH)2 content, which could be attributed to the increasing of the energy gaps for the CDs. The highly photoluminescent CDs obtained (quantum yield: 86%) were used to cultivate fluorescent carnations by a water culture method, while the results of fluorescence microscopy analysis indicated that the CDs had entered the plant tissue structure.

Employing metformin-directed carbon dots with room-temperature phosphorescent towards the dual-channel detection of L-tryptophan

Carbon dots are a novel carbon-based material with the appealing properties of inexpensive nanomaterials, low toxicity, environmental tolerance, abundance, photostability, and simplicity of synthesis. Carbon dots (CDs) have effectively distinguished themselves from other materials due to their superior properties, such as ultra-small size, good photostability, excellent biocompatibility, and tunable fluorescence properties. This study synthesized carbon dots from green algae using a hydrothermal method at 180 °C and doped with nitrogen. Green algae contain carbohydrates, proteins, and poly-unsaturated fatty acids, allowing them to produce more carbon and be used as a precursor in synthesizing carbon dots. The FT-IR and UV-Vis spectra reveal the distinct functionalization and energy gap between the surface states of CDs and N-CDs. The carbon nanoparticles were then used as photocatalysts to degrade methyl red. The results indicate that nitrogen doping is superior for reducing methyl red and has tremendous potential for environmental applications.

Carbon dots (CDs) have attracted attention in metal-free afterglow materials, but most CDs were heteroatom-containing and the afterglow emissions are still limited to the short-wavelength region. A universal approach to activate the room-temperature phosphorescence (RTP) of both heteroatom-free and heteroatom-containing CDs was developed by one-step heat treatment of CDs and boric acid (BA). The introduction of an electron-withdrawing boron atom in composites can greatly reduce the energy gap between the singlet and triplet state; the formed glassy state can effectively protect the excited triplet states of CDs from nonradiative deactivation. A universal host for embedding CDs to achieve long-lifetime and multi-color (blue, green, green-yellow and orange) RTP via a low cost, quick and facile process was developed. Based on their distinctive RTP performances, the applications of these CD-based RTP materials in information encryption and decryption are also proposed and demonstrated.