褐煤分子片段结构电子吸收光谱的理论研究

摘要

应用不同密度泛函计算了几种代表性化合物和褐煤分子片段结构的电子吸收光谱性质，考察了结构修饰与杂环原子对电子光谱性质的影响。计算结果表明，杂化泛函B3LYP和HSEH1PBE较适合这类体系电子吸收光谱的计算，预测的吸收光谱主要出现在近紫外区，随着共轭环的增加，λmax吸收移向可见光区。当共轭支链基团通过C C键和分子片段模型连接时，在可见光区(460~480 nm)有非常强的吸收。杂环原子的存在及其在五元环中的位置对电子吸收光谱有显著影响，处在相对对称的位置时，前线轨道的共轭程度较高，导致λmax吸收出现较显著的红移，预测的这些分子片段光谱性质有助于理解褐煤的光响应性质。%Electronic spectra of the lignite structural units and the effects of structural modification were ex-plored by extensive density functional calculations. Based on calibration calculations on six representative com-pounds by different functionals, the feasibility of both B3LYP and HSEH1PBE for this kind of systems was validated. Predicted absorption spectra indicate that the main bands appear in near Ultraviolet-Visible region, while for the lignite structural unit with the extended conjugated components theλmax absorption occurs in visi-ble region. Note that there are quite strong absorptions in the visible region of 460—480 nm as the side conju-gated chain is linked to the structural unit through C C. The types of hetero-atoms and their positions show remarkable effects on the electronic absorption features, and the frontier orbitals in the structural units with a symmetric hetero-atom are well delocalized, especially for LUMO, resulting in notable red-shifted absorption ofλmax . The predicted spectroscopic properties of the lignite structural units provide a basis to understand their features of light response.