Hydrophobic Carbon Dots with Aggregation-Induced Emission for Multistage Anticounterfeiting

Abstract

Anticounterfeiting work has always been a key work related to people's interests, and fluorescent anticounterfeiting labels are more common. However, the current anticounterfeiting model of fluorescent anticounterfeiting markers is relatively simple and easy to copy. It is urgent to develop anticounterfeiting markers with better anticounterfeiting ability. To this end, we prepared fluorescent carbon dots (CDs) with an aggregation-induced emission (AIE) effect in one step using 2,2-dithiodibenzoic acid (DTSA) and a urea hot solvent. Blue fluorescence at 475 nm is emitted under ultraviolet excitation in the dispersed state, while orange-red fluorescence at 618 nm is emitted in the aggregated state. The two states' fluorescence quantum yields and fluorescence lifetimes are 7.4%, 1.94 ns and 19.6%, 1.61 ns, respectively, with good crystallization properties. At the same time, due to the dehydration reaction of its carboxyl group and amino group, the consumption of a large number of carboxyl and amino groups makes it aggregate in aqueous solution, while it is dispersed in lower-polarity solvents, such as acetic acid and ethanol. The conversion of the two states can make its fluorescence change, and so a solvent-dependent multilevel anticounterfeiting ink is designed, which can be used for multilevel anticounterfeiting and information encryption.

One-step synthesis of orange–red emissive carbon dots: photophysical insight into their excitation wavelength-independent and dependent luminescence

“…The most common method for longer wavelength emission in near-infrared regions can be achieved by introducing heteroatoms into carbon lattices, resulting in defects in their framework. 18–22 Further, these red or orange emissive CDs are produced by multiple synthesis steps, 20 long reaction time 23,24 and high-temperature hydrothermal reaction 19,25 followed by complicated purification procedures, 26 such as silica-gel column chromatography 25,27 or dialysis. 9,28–30 Thus, orange–red emissive CDs with high emission intensity and excitation wavelengths of an independent nature in near-infrared regions without further post-purification methods are still highly desired.…”