Solvent effect is one of the effective pathways to regulate the fluorescence emission spectra of carbon dots (CDs). In this work, the solvent effect on fluorescence emission of CDs with functional groups has been investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. Solvation model based on density (SMD) and microsolvent-SMD models have been employed to simulate the solvent effects. The electron donating or withdrawing ability of the surface functional groups of CDs, the polarity of the solvent, and the interaction between solvent molecules and CDs were analyzed. The results indicate that microsolvent-SMD model comprehensively considers the solvent polarity and the interaction between solvent molecules and functional groups, which is more advantageous to revealing the physical nature of solvent molecules participating in fluorescence emission, resulting in the calculated fluorescence spectra closer to experimental results. The hydrogen bonds can modulate the fluorescence spectra of CDs more significantly than the solvent polarity, when the CDs are primarily characterized by n-π* transitions, hydrogen bonding induces a blue shift in the fluorescence spectrum, whereas when the CDs mainly undergo π-π* transitions, hydrogen bonding causes a red shift in the spectrum. This work provides theoretical guidance to exploit the solvent effect to achieve effective modulation of the fluorescence properties of CDs.

中文翻译：

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溶剂效应对碳点荧光发射调制机制的第一性原理研究


溶剂效应是调节碳点（CD）荧光发射光谱的有效途径之一。在这项工作中，使用密度泛函理论（DFT）和时间相关密度泛函理论（TD-DFT）方法研究了溶剂对带有官能团的碳点荧光发射的影响。基于密度的溶剂化模型（SMD）和微溶剂-SMD 模型已被用来模拟溶剂效应。分析了碳点表面官能团的给电子或吸电子能力、溶剂的极性以及溶剂分子与碳点之间的相互作用。结果表明，微溶剂-SMD模型综合考虑了溶剂极性以及溶剂分子与官能团之间的相互作用，更有利于揭示溶剂分子参与荧光发射的物理性质，导致计算的荧光光谱更接近实验结果。氢键对碳点的荧光光谱的调节作用比溶剂极性更显着，当碳点主要以n-π*跃迁为特征时，氢键会引起荧光光谱蓝移，而当碳点主要经历π-π跃迁时，氢键会引起荧光光谱蓝移。 * 跃迁、氢键导致光谱红移。这项工作为利用溶剂效应实现碳点荧光特性的有效调节提供了理论指导。