Stimuli-responsive photoluminescent (PL) materials have been widely used as fluorescent ink for data security applications. However, traditional fluorescent inks are limited in maintaining the secrecy of information because the inks are usually visible by naked eyes either under ambient light or UV-light illumination. Here, we introduced metal-free water-soluble graphitic carbon nitride quantum dots (g-CNQDs) as invisible security ink for information coding, encryption, and decryption. The information written by the g-CNQDs is invisible in ambient light and UV light, but it can be readable by a fluorescence microplate reader. Moreover, the information can be encrypted and decrypted by using oxalic acid and sodium bicarbonate as encryption reagent and decryption reagent, respectively. Our findings provide new opportunities for high-level information coding and protection by using water-soluble g-CNQDs as invisible security ink.

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Antifreeze proteins (AFPs), a type of high-efficiency but expensive and often unstable biological antifreeze, have stimulated substantial interest in the search for synthetic mimics. However, only a few reported AFP mimics display thermal hysteresis, and general criteria for the design of AFP mimics remain unknown. Herein, oxidized quasi-carbon nitride quantum dots (OQCNs) are synthesized through an up-scalable bottom-up approach. They exhibit thermal-hysteresis activity, an ice-crystal shaping effect, and activity on ice-recrystallization inhibition. In the cryopreservation of sheep red blood cells, OQCNs improve cell recovery to more than twice that obtained by using a commercial cryoprotectant (hydroxyethyl starch) without the addition of any organic solvents. It is shown experimentally that OQCNs preferably bind onto the ice-crystal surface, which leads to the inhibition of ice-crystal growth due to the Kelvin effect. Further analysis reveals that the match of the distance between two neighboring tertiary N atoms on OQCNs with the repeated spacing of O atoms along the c-axis on the primary prism plane of ice lattice is critical for OQCNs to bind preferentially on ice crystals. Here, the application of graphitic carbon nitride derivatives for cryopreservation is reported for the first time.

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The photoluminescence (PL) emission mechanism of graphitic carbon nitride (g-CN) is still ambiguous and the application of PL g-CN powder as a solid sensing platform has not been explored. Herein we highlight a strategy to prepare g-CN powder with strong green PL by doping phenyl groups in a carbon nitride network. Compared with pristine g-CN, doping of phenyl groups greatly enhances the PL efficiency and Stokes shift. Theoretical calculations based on density function theory indicate that phenyl groups change the electronic structure of the carbon nitride network and have an obvious contribution to the LUMO of phenyl-doped g-CN, which may be the main reason for the enhancement of the PL efficiency and Stokes shift. Taking advantage of the high PL efficiency, large Stokes shift and high photo-stability, phenyl-doped g-CN powder shows promising application for the imaging of latent fingerprints.

In spite of recent progress,t here is still al acko f reliable organic electrodes for Li storage with high comprehensive performance,e specially in terms of long-term cycling stability.Herein, we report an ideal polymer electrode based on anthraquinone,n amely,p olyanthraquinone (PAQ), or specifically,poly(1,4-anthraquinone) (P14AQ) and poly(1,5-anthraquinone) (P15AQ). As al ithium-storage cathode,P 14AQ showed exceptional performance,including reversible capacity almost equal to the theoretical value (260 mA hg À1 ; > 257 mA hg À1 for AQ), av ery small voltage gap between the charge and discharge curves (2.18-2.14 = 0.04 V), stable cycling performance (99.4 %c apacity retention after 1000 cycles), and fast-discharge/charge ability (release of 69 %ofthe low-rate capacity or 64 %o ft he energy in just 2min). Exploration of the structure-performance relationship between P14AQa nd related materials also provided us with deeper understanding for the design of organic electrodes.

The application of fluorescent graphitic carbon nitride (g-C 3 N 4 ) nanomaterials was limited by short photoluminescence (PL) wavelength. It is great desirable to develop g-C 3 N 4 nanomaterials with long PL wavelength and high quantum yield to expand their application. Herein phenyl-modified and sulfur doped g-C 3 N 4 (PhCNS) powders with tunable PL peak from 520 to 630 nm were prepared by copolymerization of 2,4diamino-6-phenyl-1,3,5-triazine and trithiocyanuric acid. The copolymerization process of PhCNS powders was proposed after chemical structure characterization and PL mechanism of PhCNS powders were investigated by transient fluorescence. In virtue of tunable PL color, broad PL peak, and high quantum yield, PhCNS powders were utilized to fabricate green, yellow, and white light-emitting diodes with high color quality and PhCNS nanosheets were applied for multicolor bioimaging. This work provides a pathway for exploring g-C 3 N 4 nanomaterials with long PL wavelength and facilitates their application in biocompatible optoelectronic devices, fluorescent bioimaging.