Dual Fluorescence in Glutathione-Derived Carbon Dots Revisited

Abstract

Dual-fluorescence carbon dots have great potential as nanosensors in life and materials sciences. Such carbon dots can be obtained via a solvothermal synthesis route with glutathione and formamide. In this work, we show that the dual-fluorescence emission of the synthesis products does not originate from a single carbon dot emitter, but rather from a mixture of physically separate compounds. We characterized the synthesis products with UV–vis, Raman, infrared, and fluorescence spectroscopy, and identified blue-emissive carbon dots and red-emissive porphyrin. We demonstrate an easy way to separate the two compounds without the need for time-consuming dialysis. Understanding the nature of the system, we can now steer the synthesis toward the desired product, which paves the way for a cheap and environmentally friendly synthesis route toward carbon dots, water-soluble porphyrin, and mixed systems.

From Small Molecules to Zero-Dimensional Carbon Nanodots: Chasing the Stepwise Transformations During Carbonization

“…The magnified image of N-CDs (inset of Figure 5c) shows the prominent lattice spacing close to ∼0.33 nm, which is consistent with the (002) plane of graphite. 9,22,35 Therefore, one can conclude that at the very beginning of the growth process, precursor molecules show complete amorphous quasi-spherical morphology, which eventually converts to amorphous spherical dots, and finally, during the further carbonization process, this amorphous spherical nanoparticle converts to highly crystalline CDs. Furthermore, to understand the crystalline nature of the assynthesized N-CDs, we have measured the XRD profiles of various CDs at different carbonization times (30, 60, and 480 min) (Figure S3).…”

“…However, with increasing reaction time further (60 and 120 min), N-CDs start showing excitation wavelength-independent emission spectra to some extent, in the excitation range of 300 to 400 nm. It suggests that in this wavelength range, the overall emission properties are mostly dominated by the molecular fluorophores. ,, However, by increasing growth time further (240 and 480 min), the N-CDs start showing again an excitation wavelength-dependent PL emission behavior due to the formation of various surfaces and/or defects and extended conjugated aromatic domains with large polycyclic aromatic molecules, which eventually increase the excitation wavelength-dependent emission properties by forming self-trapped excitons and facilitating the FRET process between various chromophoric domains. , For further clarification, we have measured the PL excitation (PLE) spectra at an emission wavelength of 500 nm (as depicted in Figure f). The PLE spectra match well with the absorption spectra, which suggest the clear existence of multiple emissive states and their temporal evolution during the growth process.…”

“…It suggests that in this wavelength range, the overall emission properties are mostly dominated by the molecular fluorophores. 9,34,35 However, by increasing growth time further (240 and 480 min), the N-CDs start showing again an excitation wavelength-dependent PL emission behavior due to the formation of various surfaces and/or defects and extended conjugated aromatic domains with large polycyclic aromatic molecules, which eventually increase the excitation wavelength-dependent emission properties by forming self-trapped excitons and facilitating the FRET process between various chromophoric domains. 36,37 For further clarification, we have measured the PL excitation (PLE) spectra at an emission wavelength of 500 nm (as depicted in Figure 2f).…”

“…The XPS survey spectra for all samples show the presence of C, N, and O at binding energies around 285, 400, and 531 eV, respectively (Figure S5). ,,, The high-resolution XPS C 1s and N 1s spectra are shown in Figure d,e. The high-resolution C 1s spectra of N-CDs at 30 min reaction time are deconvoluted into four peaks corresponding to various carbon species.…”

Intrinsic Dual-Emitting Carbon Quantum-Dot-Based Selective Ratiometric Fluorescent Mercaptopurine Detection

“…According to the literature, the absorption peaks in the range of 600−700 nm can be attributed to the formation of porphyrin compounds during the synthesis of CQDs in the presence of glutathione. 41,42 The fluorescence emission spectrum of the CQDs using different excitation wavelengths in the range of 350−420 nm is shown in Figure 2b. According to the obtained data, the photoluminescence (PL) of the CQDs was red shifted as the excitation wavelength increased.…”