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Graphitic Nitrogen Triggers Red Fluorescence in Carbon Dots
ACS Nano ( IF 17.1 ) Pub Date : 2017-11-20 00:00:00 , DOI: 10.1021/acsnano.7b06399
Kateřina Holá 1 , Mária Sudolská 1 , Sergii Kalytchuk 1 , Dana Nachtigallová 1, 2 , Andrey L. Rogach 3 , Michal Otyepka 1 , Radek Zbořil 1
Affiliation  

Carbon dots (CDs) are a stable and highly biocompatible fluorescent material offering great application potential in cell labeling, optical imaging, LED diodes, and optoelectronic technologies. Because their emission wavelengths provide the best tissue penetration, red-emitting CDs are of particular interest for applications in biomedical technologies. Current synthetic strategies enabling red-shifted emission include increasing the CD particle size (sp2 domain) by a proper synthetic strategy and tuning the surface chemistry of CDs with suitable functional groups (e.g., carboxyl). Here we present an elegant route for preparing full-color CDs with well-controllable fluorescence at blue, green, yellow, or red wavelengths. The two-step procedure involves the synthesis of a full-color-emitting mixture of CDs from citric acid and urea in formamide followed by separation of the individual fluorescent fractions by column chromatography based on differences in CD charge. Red-emitting CDs, which had the most negative charge, were separated as the last fraction. The trend in the separation, surface charge, and red-shift of photoluminescence was caused by increasing amount of graphitic nitrogen in the CD structure, as was clearly proved by XPS, FT-IR, Raman spectroscopy, and DFT calculations. Importantly, graphitic nitrogen generates midgap states within the HOMO–LUMO gap of the undoped systems, resulting in significantly red-shifted light absorption that in turn gives rise to fluorescence at the low-energy end of the visible spectrum. The presented findings identify graphitic nitrogen as another crucial factor that can red-shift the CD photoluminescence.

中文翻译:

石墨氮触发碳点中的红色荧光

碳点(CD)是一种稳定且高度生物相容的荧光材料,在细胞标记,光学成像,LED二极管和光电技术中具有巨大的应用潜力。由于它们的发射波长可提供最佳的组织穿透力,因此红色发射的CD对于生物医学技术中的应用尤为重要。当前的合成策略使得能够红移发射包括增加CD粒径(SP 2由适当的合成策略域)和调整的CD的表面化学性质与合适的官能团(É(,羧基)。在这里,我们介绍了一种制备全色CD的优雅方法,该CD在蓝色,绿色,黄色或红色波长下具有可控制的荧光。分两步进行的过程涉及从柠檬酸和尿素的甲酰胺中合成CD的全色发光混合物,然后根据CD电荷的差异通过柱色谱法分离各个荧光部分。负电荷最多的发红光的CD被分离为最后一个部分。XPS,FT-IR,拉曼光谱和DFT计算清楚地证明,CD结构中石墨氮的增加是导致光致发光的分离,表面电荷和红移的趋势。重要的是,石墨氮会在未掺杂系统的HOMO-LUMO间隙内产生中间能带状态,导致明显的红移光吸收,进而在可见光谱的低能端产生荧光。提出的发现确定了石墨氮是另一个可以使CD光致发光的关键因素。
更新日期:2017-11-21
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