Modulating Triplet Excited-State Energy in Phosphorescent Carbon Dots for Information Encryption and Anti-Counterfeiting

Room-temperature phosphorescent carbon dots (RTP-CDs) may be used in anti-counterfeiting, information encryption, and optoelectronic devices, but modulating their triplet-state energy is still challenging. Here, a type of RTP-CDs was developed via hydrothermal polymerization-carbonization of azamacrocycle and poly(acrylic acid). The introduction of nitrogen heterocycle promotes the intersystem crossing from the singlet state to the triplet state, and the functional groups of CDs can form interdot hydrogen bonds to protect the triplet state. In addition, the uncarbonized heterocycle groups in the CDs provide coordination sites for metal ions. In this case, the excited triplet-state energy of CDs is quenched by paramagnetic ions (Co²⁺ and Cu²⁺) or transfers to luminescent ions (Tb³⁺ and Eu³⁺). Furthermore, the modulation of the triplet state by metal ion binding was demonstrated in information encryption and anti-counterfeiting applications.