Wang Boyang, Wei Zhihong, Sui Laizhi, Yu Jingkun, Zhang Baowei, Wang Xiaoyong, Feng Shengnan, Song Haoqiang, Yong Xue, Tian Yuxi, Yang Bai, Lu Siyu
Green Catalysis Center, and College of Chemistry, Zhengzhou University, 450000, Zhengzhou, China.
Key Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Jiangsu Key Laboratory of Vehicle Emissions Control, Nanjing University, 210023, Nanjing, China.
Light Sci Appl. 2022 Jun 6;11(1):172. doi: 10.1038/s41377-022-00865-x.
Due to the complex core-shell structure and variety of surface functional groups, the photoluminescence (PL) mechanism of carbon dots (CDs) remain unclear. o-Phenylenediamine (oPD), as one of the most common precursors for preparing red emissive CDs, has been extensively studied. Interestingly, most of the red emission CDs based on oPD have similar PL emission characteristics. Herein, we prepared six different oPD-based CDs and found that they had almost the same PL emission and absorption spectra after purification. Structural and spectral characterization indicated that they had similar carbon core structures but different surface polymer shells. Furthermore, single-molecule PL spectroscopy confirmed that the multi-modal emission of those CDs originated from the transitions of different vibrational energy levels of the same PL center in the carbon core. In addition, the phenomenon of "spectral splitting" of single-particle CDs was observed at low temperature, which confirmed these oPD-based CDs were unique materials with properties of both organic molecules and quantum dots. Finally, theoretical calculations revealed their potential polymerization mode and carbon core structure. Moreover, we proposed the PL mechanism of red-emitting CDs based on oPD precursors; that is, the carbon core regulates the PL emission, and the polymer shell regulates the PL intensity. Our work resolves the controversy on the PL mechanism of oPD-based red CDs. These findings provide a general guide for the mechanism exploration and structural analysis of other types of CDs.
由于碳点（CDs）具有复杂的核壳结构和多样的表面官能团，其光致发光（PL）机制仍不明确。邻苯二胺（oPD）作为制备红色发光碳点最常用的前驱体之一，已被广泛研究。有趣的是，大多数基于oPD的红色发光碳点具有相似的PL发射特性。在此，我们制备了六种不同的基于oPD的碳点，发现纯化后它们具有几乎相同的PL发射光谱和吸收光谱。结构和光谱表征表明它们具有相似的碳核结构，但表面聚合物壳不同。此外，单分子PL光谱证实这些碳点的多模态发射源于碳核中同一PL中心不同振动能级的跃迁。另外，在低温下观察到单粒子碳点的“光谱分裂”现象，这证实这些基于oPD的碳点是具有有机分子和量子点特性的独特材料。最后，理论计算揭示了它们潜在的聚合模式和碳核结构。此外，我们提出了基于oPD前驱体的红色发光碳点的PL机制；即，碳核调节PL发射，聚合物壳调节PL强度。我们的工作解决了基于oPD的红色碳点PL机制的争议。这些发现为其他类型碳点的机制探索和结构分析提供了一般性指导。
