Insights into Fluorophores of Dual-Emissive Carbon Dots Derived by Naphthalenediol Solvothermal Synthesis

Abstract

Versatile species have been increasingly recognized as important components and possible fluorescence origins in carbon dots synthesized via a bottom-up route. Herein, we use 2,7-naphthalenediol and dimethylformamide as precursors to synthesize a novel type of carbon dots via an ethanothermal reaction. Two main luminescent components with entirely different structures, including molecular fluorophores and carbogenic nanodots, are independently acquired by column chromatography separation and dialysis, respectively. Through detailed nuclear magnetic resonance studies, the chemical structure of molecular fluorophores has been elucidated as 8-ethoxy-3H-cyclopenta­[a]­naphthalen-3-one (ECNO), while the carbon dot (C-dot) is characterized as a carbon core with bound fluorophores. A comparative study between ECNO and C-dots is systematically conducted in terms of steady- and transient-state emission spectra, environmental sensitivity, and stability. ECNO shows a single green and excitation-wavelength-independent emission, but it is highly sensitive to the solution pH and solvent polarity. As the carbogenic counterpart, C-dots show dual emission comprising a blue broad and a yellow narrow-band emission. Besides, C-dots exhibit higher photo- and thermal stability than ECNO. The state of fluorophores (unbound state vs bound state) causes these dramatic differences in the optical behaviors between ECNO and C-dots. By virtue of their distinctive properties, ECNO can be used as a fluorescent filler to fabricate smart polymer composites and anti-counterfeiting inks, while C-dots find applications as phosphors in white-light emitting diodes.

Carbon Dots: Synthesis, Properties and Applications

“…Through a solvothermal method, Zheng et al synthesized full-color emitting CQDs by changing the reactant concentrations in the reaction solvent [102], and possible synthesis mechanisms for full-color emitting CQDs is shown in Figure 7e. Similarly, He and his coworker found that versatile impurities (as luminescent components) originating from the ethanothermal process can also mask the luminescence of the CQDs [103]. For example, molecular fluorophore (8-ethoxy-3H-cyclopenta naphthalen-3-one, ECNO) were produced in the synthesis process and showed a single green and excitation-wavelength-independent emission.…”

Assembly of Centimeter-Scale Plasmonic Nanocavities for Bright and Ultrafast Emission of Red Carbon Dots

“…High-resolution TEM reveals clear lattice fringes with a spacing of 0.21 nm, corresponding to the (100) plane of graphite. Besides its carbon core, R-CDs also has rich oxygen- and nitrogen-containing groups (Figure S2), which play an important role in the fluorescence of carbon dots. , The R-CDs show good solubility in most organic solvents but insolubility in water, and its solution exhibits excitation wavelength independence and solvent polarity insensitivity (Figure S3). To fabricate an emissive layer, the R-CDs are dispersed into the PMMA matrix using toluene as a solvent, and the adjacent polymer layers using hydrophilic solvents have little effect on their fluorescence.…”

Monochromatic Blue and Switchable Blue‐Green Carbon Quantum Dots by Room‐Temperature Air Plasma Processing

“…Few reports can be found in the literature regarding dual‐emissive CQDs synthesis with the emission color combinations of blue–red, [ 37 ] blue–green, [ 38 ] green–red, [ 39 ] red–yellow, [ 40 ] red–orange, [ 41 ] and blue–yellow. [ 42 ] Each of these studies has been conducted via thermal synthetic routes such as hydrothermal, solvothermal or microwave techniques which require temperatures above 85 °C within the reaction medium. Longer preparation times were also necessary and varied from hours to days in hydrothermal and solvothermal methods.…”