Despite the various synthesis methods to obtain carbon dots (CDs), the bottom-up methods are still the most widely administrated route to afford large-scale and low-cost synthesis. However, as CDs are developed with increasing reports involved in producing many CDs, the structure and property features have changed enormously compared with the first generation of CDs, raising classification concerns. To this end, a new classification of CDs, named carbonized polymer dots (CPDs), is summarized according to the analysis of structure and property features. Here, CPDs are revealed as an emerging class of CDs with distinctive polymer/carbon hybrid structures and properties. Furthermore, deep insights into the effects of synthesis on the structure/property features of CDs are provided. Herein, the synthesis methods of CDs are also summarized in detail, and the effects of synthesis conditions of the bottom-up methods in terms of the structures and properties of CPDs are discussed and analyzed comprehensively. Insights into formation process and nucleation mechanism of CPDs are also offered. Finally, a perspective of the future development of CDs is proposed with critical insights into facilitating their potential in various application fields.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201901316

Evolution and Synthesis of Carbon Dots: From Carbon Dots to Carbonized Polymer Dots

Thermally activated delayed fluorescence (TADF) materials are inspiring intensive research in optoelectronic applications To date, most of the TADF materials are limited to metal-organic complexes and organic molecules with lifetimes of several microseconds/milliseconds that are sensitive to oxygen We report a facial and general "dots-in-zeolites" strategy to in situ confine carbon dots (CDs) in zeolitic matrices during hydrothermal/solvothermal crystallization to generate high-efficient TADF materials with ultralong lifetimes The resultant CDs@zeolite composites exhibit high quantum yields up to 5214% and ultralong lifetimes up to 350 ms at ambient temperature and atmosphere This intriguing TADF phenomenon is due to the fact that nanoconfined space of zeolites can efficiently stabilize the triplet states of CDs, thus enabling the reverse intersystem crossing process for TADF Meanwhile, zeolite frameworks can also hinder oxygen quenching to present TADF behavior at air atmosphere This design concept introduces a new perspective to develop materials with unique TADF performance and various novel delayed fluorescence-based applications

Carbon dots in zeolites: A new class of thermally activated delayed fluorescence materials with ultralong lifetimes

Long-wavelength, multicolor, and white-light emitting carbon-based dots: Achievements made, challenges remaining, and 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.

A Universal Strategy for Activating the Multicolor Room-Temperature Afterglow of Carbon Dots in a Boric Acid Matrix.

Fluorescent probes with both excitation and emission in the near-infrared (NIR) region are highly attractive in the field of bioimaging. Herein, NIR emissive carbon dots (CDs, λmax = 683 nm) capable of excitation with a NIR femtosecond pulse laser (850 nm) are reported for the first time. The NIR CDs also hold a variety of superior features including excellent water dispersibility, narrow emission bands, and high quantum yields (QY = 16.8%). Further studies reveal that the emission of the NIR CDs derives predominantly from the surface molecular state mechanism. More interestingly, the NIR CDs are verified to have very low cytotoxicity and show capabilities for two-photon fluorescence bioimaging. Finally, the NIR CDs are shown to be easily modified with fluorescein isothiocyanate (FITC) and moved into living cells. These findings demonstrate that the as-prepared NIR CDs could not only be potentially employed for deep-tissue two-photon bioimaging, but also used as an effective carrier for delivery of drugs that can't (or hardly) enter into living cells directly.

Near-infrared emissive carbon dots for two-photon fluorescence bioimaging

Hydrophilic N-doped carbogenic nanodots (denoted as CNDs) have been prepared from a N-methylpiperazine-templated zeolite precursor by calcination and NaOH treatment. The isolated CNDs exhibit tunable photoluminescence according to the concentration and pH value of aqueous dispersions of the CNDs. Fine-tuning of the fluorescence emission wavelength across the entire visible spectrum can be easily achieved by varying the concentration of the CND dispersions. Meanwhile, both the emission wavelength and intensity of the photoluminescence can be tuned by controlling the pH value of the CND dispersion. The pyrolysis of organic templates confined in nanoporous zeolites represents a new approach to controlling the optical properties of CNDs, which may open more opportunities in applications such as multimodal sensing and full-color displays.

/pdf/carbogenic-nanodots-derived-from-organo-templated-zeolites-2h00zrnfa4.pdf

Carbogenic nanodots derived from organo-templated zeolites with modulated full-color luminescence

We introduced Pt3Co nanoparticles (NPs) into the hole-injection layer (HIL) in organic light-emitting devices and demonstrated a highly efficient green OLED. The Pt3Co NPs as the hole-traps adjusted the hole transport property in the PEDOT:PSS layer, consequently resulting in a balanced charge injection into the emission layer and enhancing the efficiency of the devices. The theory analysis also indicated that the hole traps induced by Pt3Co NPs played an important role in improving the charge balance in the Pt3Co-containing devices. The studies on the transient resolution photoluminescence (TRPL) indicated that the lifetime of the excitons was not influenced by the Pt3Co NPs, even though a very thin spacer was introduced. The Pt3Co-containing device exhibited a 73% higher current efficiency compared with the conventional device without Pt3Co NPs.

Jing Wang

Papers

Carbogenic nanodots derived from organo-templated zeolites with modulated full-color luminescence

Highly efficient organic light-emitting devices by introducing traps in the hole-injection layer