Amorphization of Purely Organic Phosphors into Carbon Dots to Activate Matrix-Free Room-Temperature Phosphorescence for Multiple Applications

Abstract

The insufficiency of effectively activating purely organic phosphorescence has greatly limited the development and application of purely organic phosphors. Herein, amorphization of purely organic phosphors into carbon dots (C-dots), namely, amorphization strategy, was designed for activating matrix-free room-temperature phosphorescence (RTP) of C-dots. Using citric acid and 2,4,6-trihydrazinyl-1,3,5-triazine (THT) as precursors, the obtained C-dots reserved the ordered structure similar to a THT single crystal in the interior of C-dots. The doped triazine overing is critical for RTP; it not only provides the n–π* transition center but also plays a key role in facilitating the intersystem crossing. The weak interactions among THT molecules, such as π···π stacking and hydrogen bond interactions, and the hydrogen bond among functional groups in the interior of C-dots, together with the steric hindrance formed by polymer-like structures of C-dots, served as matrices to embed and immobilize the emissive center, resulting in the afterglow with a lifetime of 66.4 ms. C-dot-based RTP was successfully used for digital encryption, information protection, and antibacterial protection. Most importantly, the universality of the amorphization strategy provided a simple and advantageous pathway for the activation of C-dot-based matrix-free RTP.

One-Pot Three Carbon Dots with Various Lifetimes Rooted in Different Decarboxylation Degrees for Matrix-Free, Anti-Oxygen, and Time-Resolved Information Encryption and Cellular Imaging

“…The Δ E ST was ∼0.34 eV for Pw-C-dots and ∼0.39 eV for Py-C-dots. These small Δ E ST values were favorable for effectively populating triplet excitons and consequently activating long-lived RTP. − The origin of the RTP of the Pw-C-dots and Py-C-dots were thus reasonably explained. Compared with the trimellitic acid (TA)-sourced sole C-dots with an aggregation-induced RTP characteristic, though an isomeride precursor with TA, our TMA source, however, produced three C-dots with two RTP products owing to the differences in the decarboxylation degree at much higher temperatures.…”

“…These groups featuring n –π* transition absorption and emission characteristics are formed by the reaction between/among precursors, carbonization at high temperatures, and/or oxidation by water or oxidants. When they anchored on the surface of the C-dots, various matrices were required to immobilize the external n –π* emissive center for activating RTP. − Reversely, if these groups were embedded in the interior of C-dots, the internal hydrogen bonds and polymer-like covalent bonds of C-dots as self-matrices can “lock” the internal triplet excitons, efficiently suppressing the nonradiative relaxation. − Therefore, long-lived afterglows in the exterior and interior of the C-dots were observed. Two types of matrix-free RTPs of the C-dots were fabricated due to the low energy gap between S 1 and T 1 (Δ E ST ) , and heavy atom effect. − Unfortunately, many C-dots-based RTPs can be observed in the solid state because these C-dots are highly hydrophilic and easily infiltrated by water containing dissolved oxygen, resulting in the insufficiency of RTP in aqueous solution .…”

Recent Advances of Carbon Dots with Afterglow Emission

“…One approach is to introduce heteroatoms or halogen atoms to promote effective ISC, so as to obtain matrix‐free self‐protection CDs (mainly RTP). [ 25,48,69–71 ] The other one is to build different types of rigid environments to limit the motions of chromophores and reduce the nonradiative transition of triplet excitons, so as to obtain matrix‐protected CDs (including RTP, DF, and LPL emission). [ 5,6,13,60,72–74 ]…”

Evolution and fabrication of carbon dot-based room temperature phosphorescence materials

“…Currently, researchers oen choose polymers or their monomers, cross-linkable reactants, molecules doped with heteroatoms and larger conjugated structures as precursors. [86][87][88][89][90][91][92][93][94][95][96][98][99][100][101][102][103][104][105][106][107][108][109]131,132 The relevant achievements are shown in Table 2.…”