The most commonly observed phenomena in carbon nanodots (CNDs) are the strong excitation wavelength dependent multicolor fluorescence emission and the particle size distribution between 3–5 nm observed using a transmission electron microscope (TEM). However, it is not evident yet whether the emission originates from the particles observed using a TEM. In this article, we show that hydrothermal treatment of citric acid produces methylenesuccinic acid, which gives rise to hydrogen-bonded nano-assemblies with CND-like properties. While single crystal X-ray crystallography confirms the structure of methylenesuccinic acid, fluorescence correlation spectroscopy (FCS) confirms the presence of a molecular fluorophore with an average hydrodynamic diameter of ∼0.9 nm. This size is much smaller than the size of the particles observed using a TEM. We conclude that the particles observed using a TEM are the drying mediated nanocrystals of methylenesuccinic acid.

中文翻译：

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小分子有机纳米晶体的性质类似于碳纳米点

碳纳米点（CND）中最常观察到的现象是强激发波长相关的多色荧光发射，以及使用透射电子显微镜（TEM）观察到的3–5 nm之间的粒径分布。但是，尚不清楚发射是否源自使用TEM观察到的颗粒。在本文中，我们表明柠檬酸的水热处理会生成亚甲基琥珀酸，这会产生具有CND样性质的氢键结合的纳米组件。单晶X射线晶体学证实了亚甲基琥珀酸的结构，而荧光相关光谱法（FCS）证实了平均流体动力学直径约为0.9 nm的分子荧光团的存在。该尺寸远小于使用TEM观察到的颗粒的尺寸。