Key Laboratory for Power Machinery and Engineering of Ministry of Education, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center, Thuwal 23955-6900, Saudi Arabia.
Spectrochim Acta A Mol Biomol Spectrosc. 2020 Jan 5;224:117450. doi: 10.1016/j.saa.2019.117450. Epub 2019 Aug 5.
Laser-induced fluorescence (LIF) is an effective technique for non-intrusive and on-line measurement of PAHs in sooting flames but it is still need further investigation due to the complexity of PAH fluorescence characteristics. Therefore, in-depth investigations on the fluorescence spectroscopy of PAHs with different molecular structures are relevant. In this study, we investigated the fluorescence spectrum characteristics of 13 gas-phase PAHs using LIF measurement and time-dependent density functional theory (TD-DFT) calculation. The experimental results showed that the fluorescence emission wavelengths increased with more aromatic (benzenoid) rings, but this relationship no longer existed when the PAH molecules contain the five-membered ring structures. The TD-DFT calculation showed that the fluorescence emission wavelength ranges of PAHs with different molecular structures were dominantly determined by the electronic structures of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and their energy gaps. It was found that the saturated aliphatic branched chains (methyl and ethyl) only slightly influenced the LIF spectra, while the unsaturated aliphatic branched chains (ethenyl and ethynyl) caused remarkable redshifts. The TD-DFT results indicated that the aliphatic branched chains changed the electric structures of HOMO and LUMO of the core aromatic rings, and then influence the fluorescence emission wavelength ranges.
激光诱导荧光（LIF）是一种非侵入式和在线测量 soot 火焰中多环芳烃（PAHs）的有效技术，但由于 PAH 荧光特性的复杂性，仍需要进一步研究。因此，深入研究具有不同分子结构的 PAHs 的荧光光谱特性是相关的。在这项研究中，我们使用 LIF 测量和含时密度泛函理论（TD-DFT）计算研究了 13 种气相 PAHs 的荧光光谱特征。实验结果表明，荧光发射波长随芳香（苯型）环数的增加而增加，但当 PAH 分子含有五元环结构时，这种关系不再存在。TD-DFT 计算表明，不同分子结构的 PAHs 的荧光发射波长范围主要由最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）及其能隙的电子结构决定。研究发现，饱和脂肪支链（甲基和乙基）仅对 LIF 光谱略有影响，而不饱和脂肪支链（乙烯基和乙炔基）则导致明显的红移。TD-DFT 结果表明，脂肪支链改变了核心芳香环的 HOMO 和 LUMO 的电子结构，从而影响了荧光发射波长范围。
