Abstract

Carbon dots keep attracting attention in multidisciplinary fields, motivating the development of new compounds. Phenylenediamine C6H4(NH2)2 dots are known to exhibit colorful emission, which depends on size, composition, and the functional surface groups, forming those structures. While quite a few fabrication protocols have been developed, the quantum yield of phenylenediamine dots still does not exceed 50% owing to undesired fragment formation during carbonization. Here, we demonstrate that an ethylene glycol-based environment allows obtaining multicolor high-quantum-yield phenylenediamine carbon dots. In particular, a kinetic realization of solvothermal synthesis in acidic environments enhances carbonization reaction yield for meta phenylenediamine compounds and leads to quantum yields, exciting 60%. Reaction yield after the product’s purification approaches 90%. Furthermore, proximity of metal ions (Nd3+, Co3+, La3+) can either enhance or quench the emission, depending on the concentration. Optical monitoring of the solution allows performing an accurate detection of ions at picomolar concentrations. An atomistic model of carbon dots was developed to confirm that the functional surface group positioning within the molecular structure has a major impact on dots’ physicochemical properties. The high performance of new carbon dots paves the way toward their integration in numerous applications, including imaging, sensing, and therapeutics.

Highlights

  • Carbon dots (CDs), which emerged as side products in a single-walled carbon nanotube assembly,[1] are an expanding field for investigation owing to their low-cost facile fabrication[2,3] and quite a few remarkable properties.[4]

  • Geometry optimization of the samples was performed by the Broyden−Fletcher−Goldfarb−Shanno (BFGS) routine using the Gaussian plane-wave (GPW) method with the combined density functional of B88 and LYP20,21, where all atoms were relaxed until the residual force was smaller than 0.05 eV/Å

  • Relevant CD concentrations can be straightforwardly quantified with the aid of conventional spectroscopic tools, which are elaborated in detail in Section 3.5 and in the Supporting information

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Summary

INTRODUCTION

Carbon dots (CDs), which emerged as side products in a single-walled carbon nanotube assembly,[1] are an expanding field for investigation owing to their low-cost facile fabrication[2,3] and quite a few remarkable properties.[4]. The bottom-up methods have several advantages, including lower cost, scaling-up capabilities, improved size uniformity, and higher quantum yield of the product, according to recent reports.[10] Solvothermal synthesis, being applied at relatively mild conditions, is one of the simplest facile approaches, allowing one to obtain different fluorescent properties.[11] The majority of CDs emit light in the blue spectral range, and a few CDs were found to emit red light. Oxygen (O) dopants cause a spectral shift, pushing emission lines to green and yellow.[7,12] the fluorescence properties of the reaction products can be controlled by changing reaction conditions in bottom-up approaches. Analytic and qualitative techniques, including high-performance liquid chromatography (HPLC), X-ray photoelectron spectroscopy (XPS), and liquid chromatography-mass spectrometry (LCMS), provide new insights into the carbonization process, allowing one to analyze RY and supply further information on the chemical properties. Metal-enhancement fluorescence was observed at subnanomolar ion concentrations, paving the way to sensing applications (Figure 1)

EXPERIMENTAL SECTION
RESULTS AND DISCUSSION
SUMMARY
■ ACKNOWLEDGMENTS
■ REFERENCES

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