Study on fluorescence spectroscopy of PAHs with different molecular structures using laser-induced fluorescence (LIF) measurement and TD-DFT calculation

Yiran Zhang; Peng Liu; Youping Li; Reggie Zhan; Zhen Huang; He Lin

doi:10.1016/j.saa.2019.117450

Study on fluorescence spectroscopy of PAHs with different molecular structures using laser-induced fluorescence (LIF) measurement and TD-DFT calculation

Spectrochim Acta A Mol Biomol Spectrosc. 2020 Jan 5:224:117450. doi: 10.1016/j.saa.2019.117450. Epub 2019 Aug 5.

Authors

Yiran Zhang¹, Peng Liu², Youping Li¹, Reggie Zhan¹, Zhen Huang¹, He Lin³

Affiliations

¹ Key Laboratory for Power Machinery and Engineering of Ministry of Education, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
² King Abdullah University of Science and Technology (KAUST), Clean Combustion Research Center, Thuwal 23955-6900, Saudi Arabia.
³ Key Laboratory for Power Machinery and Engineering of Ministry of Education, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. Electronic address: linhe@sjtu.edu.cn.

PMID: 31422341
DOI: 10.1016/j.saa.2019.117450

Abstract

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.

Keywords: Aliphatic branched chains; Electronic emission characteristics; HOMO and LUMO; Laser-induced fluorescence (LIF) spectra; Molecular structures; Polycyclic aromatic hydrocarbons (PAHs); TD-DFT calculation.