Precise Regulation Strategy for Fluorescence Wavelength of Aggregation-Induced Emission Carbon Dots

Abstract

Aggregation-induced emission (AIE) carbon dot (CDs) in solid state with tunable multicolor emissions have sparked significant interest in multidimensional anti-counterfeiting. However, the realization of solid-state fluorescence (SSF) by AIE effect and the regulation of fluorescence wavelength in solid state is a great challenge. In order to solve this dilemma, the AIE method to prepare multi-color solid-state CDs with fluorescence wavelengths ranging from bright blue to red emission is employed. Specifically, by using thiosalicylic acid and carbonyl hydrazine as precursors, the fluorescence wavelength can be accurately adjusted by varying the reaction temperature from 150 to 230 °C or changing the molar ratio of the precursors from 1:1 to 1:2. Structural analysis and theoretical calculations consistently indicate that increasing the sp² domains or doping with graphite nitrogen both cause a redshift in the fluorescence wavelength of CDs in the solid state. Moreover, with the multi-dimensional and adjustable fluorescence wavelength, the application of AIE CDs in the fields of multi-anti-counterfeiting encryption, ink printing, and screen printing is demonstrated. All in all, this work opens up a new way for preparing solid-state multi-color CDs using AIE effect, and further proposes an innovative strategy for controlling fluorescence wavelengths.

Keywords: aggregation‐induced emission (AIE); graphite nitrogen doping; multi‐color emission; multi‐information encryption; sp2 domains.

Scheme 1

Illustration of T‐CCDs formation.

Figure 1

a–d) TEM image and the size distribution of T‐CCDs. e) XRD image of T‐CCDs. f) FT‐IR spectra of T‐CCDs g). XPS spectra of T‐CCDs. h) ¹³C NMR of T‐CCDs. i) ¹H NMR spectra of T‐CCDs. j) Raman spectra of T‐CCDs.

Figure 2

–d) UV–vis absorption, FL excitation (Ex), and emission (Em) of as‐prepared T‐CCDs 1–4 powder. e–h) Fluorescence emission of T‐CCDs1‐4 powder under different excitation wavelengths. i–l) Structural models and the calculation of LUMO and HUMO for T‐CCDs1‐4.

Figure 3

a–c) UV–vis absorption, FL excitation (Ex), and emission (Em) of as‐prepared T‐CCDs powder. d–f) The 3D contour fluorescence emission spectra of T‐CCDs. T‐CCDs5 (a,d) T‐CCDs6 (b,e), and T‐CCDs7 (c,f).

Figure 4

a) N1s XPS spectra of T‐CCDs5‐7. b) Structural models and the calculation of LUMO and HUMO for T‐CCDs5‐7.

Figure 5

a–c) Fluorescence emission spectra of the T‐CCDs as‐prepared solution with varying volume ratio of water. d–f) photographs of the T‐CCDs as‐prepared solution with varying contents of water. g–i) Fluorescence lifetime decay of the T‐CCDs Powder and solution. a,d,g) T‐CCDs5, b,e,h) T‐CCDs6, and c,f,i) T‐CCDs7.

Figure 6

Application of T‐CCDs in multi‐information encryption.