High quantum yields (QY) and stable performances are prerequisites for implementing carbon dots in practical applications. In this study, we demonstrate that nitrogen-doped carbon dots (N-CDs), which were prepared via the hydrothermal treatment of citric acid (CA) and tris(hydroxymethyl)methyl aminomethane (Tris), have a high QY of 75%, together with excellent thermal and photo stability. These N-CDs deliver an excellent thermal stability performance over the temperature range of 25 °C to 95 °C, and even at a heating temperature of 90 °C for 360 min. Upon exposure to UV illumination with a radiant intensity of 20 mW cm⁻², 96% fluorescence intensity is retained. This florescence stability performance is probably due to the chemical composition and steric effect of the nitrogen-doping agent. Furthermore, the remarkable optical properties of these N-CDs allow them to be used as invisible ink for loading important information and advanced anti-counterfeiting.

In this study, solvent-dependent emitting carbon dots (CDs) were synthesized by simple one-step hydrothermal treatment of o-phenylenediamine (oPD). The as-prepared carbon dots (o-CDs) exhibited multi-color emission and strict excitation-independent luminescence characteristics in different solvents. Moreover, multi-color emissive o-CDs/polymer films were achieved through integrating the o-CDs with different polymer matrices. Interestingly, our experimental results demonstrated that distinctive o-CDs can also be used as fluorescent probes directly for visual and quantitative detection of water in different organic solvents. These investigations broaden the application of CDs and provide an easy method to quantitatively detect the presence of water in organic solvents.

Pyrene is a quite promising structural unit for HLCT emitters, and deep-blue OLEDs showing quite high brightness over 10 000 cd m⁻² and EQE_max over 10.5% have been achieved.

The photoluminescence (PL) and electroluminescence (EL) properties of two highly efficient excited state intramolecular proton transfer (ESIPT) molecules, 2-(2′-hydroxyphenyl)oxazoles containing one triphenylamine (TPA) (1) and two TPAs (2) respectively, are studied systematically. The enol-forms of both 1 and 2 possess highly hybridized local and charge transfer (HLCT) excited state character, while their excited-state keto-forms are not of obvious HLCT character. A 1-based device exhibits green-white electroluminescence with Commission Internationale d’Eclairage (CIE) coordinates of (0.25, 0.41) and a high external quantum efficiency (EQE) up to 5.3%, which is the highest EQE value recorded for single molecular white light-emitting materials. A 2-based device shows sky-blue emission with CIE coordinates of (0.18, 0.16) and an EQE of 8.0%, which is the highest EQE in the reported HLCT materials. The fluorescence intensities of the enol-forms of 1 and 2 in EL spectra are increased remarkably relative to their PL spectra. Experimental data and theoretical calculations reveal a new ESIPT equilibrium with a reverse intersystem crossing (RISC) process arising from the HLCT character. In EL, the RISC of the enol-form excitons from the triplet state to the singlet state triggers an increase in the number of enol-form singlet excitons, which further leads to a shift of the ESIPT equilibrium towards an enhanced enol-form emission. Thus, the difference between the ESIPT equilibria in PL and EL may be ascribed to the HLCT character of the enol-form excited state.