Color‐Tunable Carbon Dots with Aggregation‐Induced Emission Constructed by FRET between Surface Luminescence Centers

Abstract

As a class of new fluorescent materials, carbon dots (CDs) have drawn widespread attention by virtue of their tunable photoluminescence (PL), excellent biocompatibility, and novel physicochemical properties. Unfortunately, in solid state, most CDs experience serious aggregation‐caused quenching (ACQ). In this work, color‐tunable CDs with aggregation‐induced emission (AIE) are prepared by simply changing the filling ratio of the autoclave. The obtained CDs show dual emission (green/red) in solid state, and the fluorescent color can be tuned from green to red. These CDs all exhibit blue fluorescence in dilute solution, and aggregation‐induced redshift behaviors are observed when the CDs form aggregates. Structural and optical characterizations prove that blue fluorescence is contributed by the carbon cores, whereas the green/red emission is attributed to the surface groups. Multicolor fluorescence is caused by increased fluorescence resonance energy transfer (FRET) efficiency among the dual emission (green/red) peaks from g‐CDs to r‐CDs. Surprisingly, delayed fluorescence (DF) of CDs are brightened by inserting the CDs into poly(vinyl alcohol) (PVA) films, which can be easily recognized by the naked eyes with a lifetime up to ms. Finally, owing to the unique AIE and DF properties, the four CDs can be applied to multimodal advanced anti‐counterfeiting and information encryption.

Chiral Aggregation-Induced Emission Carbon Dot-Based Multicolor and Near-Infrared Circularly Polarized Delayed Fluorescence via a Light-Harvesting System

“…The SEM image shows that the CDs cluster to form irregular geometric structures that are micrometers in size (Figure S4). The SEM images of the l -CD powder also show a similar geometric structure (Figure S5), which may be responsible for the fact that the XRD of l -CDs differs from that of most reported CDs with a broad peak …”

“… The S 2p bands reveal the existence of S–C (163.3 eV) and S–S (164.5 eV) groups (Figure i and Figure S3d). The relative contents of different functional groups are listed in Table S2. According to the results presented above, the CDs inherit part of the structure of the precursors, which are essential for the retention of the chiral structure .…”

“…The SEM images of the L-CD powder also show a similar geometric structure (Figure S5), which may be responsible for the fact that the XRD of L-CDs differs from that of most reported CDs with a broad peak. 45 To further explore the influence of aggregation on the optical properties, the UV−vis absorption spectra at different CD concentrations in an acetic acid solution were measured (Figure S6). We found that at a low concentration (<0.1 mg/mL), the CD solution showed no absorption in the visible region after 350 nm.…”

Recent advances in fluorescence and afterglow of CDs in matrices

“…Using dithiosalicylic acid (DTSA) with disulfide bonds and urea as the raw materials and only one set of precursors, Li's group proposed a strategy for the rapid preparation of color-tunable AIE CDs and embedding them in PVA to achieve multicolor delayed fluorescence (DF) by changing the filling ratio. 138 Modulating the degree of aggregation of CDs through the three-dimensional space of the matrix to change the interactions between electrons is an effective strategy for achieving efficient multicolor afterglow emission in one step. In Shan's group, citric acid was used as the carbon source, CDs were obtained in NaOH by a microwave-assisted in situ carbonation condensation process, and the ratio of NaOH was changed to produce multicolor RTP CDs with adjustable wavelengths ranging from 483 to 635 nm and adjustable lifetimes ranging from 58 to 389 ms. 139 In this system, the ionization of the carboxyl groups in the CDs and NaOH results in the formation of a large number of ionic bonds and a rigid crystal structure that suppresses nonradiative transitions and promotes ISC.…”