1. School of Science, Jiangnan University, Wuxi 214122, China 2. School of Internet of Things Engineering, Jiangnan University, Wuxi 214122, China 3. Key Laboratory of Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology，Sichuan University, Chengdu 610064, China 4. College of Energy and Electrical Engineering, Hohai University, Nanjing 210098, China
Abstract：The molecule structures of Ponceau 4R in ground state and the excited state wereoptimized by employing the Gaussian 09W program package. In addition, the electronic structure and frontier orbital of the ground state, the emission wavelength of the excited state was also investigated. And then, the Edinburgh FLS920P fluorescence spectrometer was applied to the measurement of the fluorescence spectra of cochineal solution, and the emission spectra was obtained. The calculated emission wavelength had a good coincidence with the experiment data, which indicates that the optimized structures mentioned above are reasonable. The structures comparison between the ground state and the excited state was also performed to analyze the mechanism of fluorescence spectrum. It can be concluded that the molecule structure of excited state is nearly planar, so Ponceau 4R is thought to have strong fluorescent characteristics, the emission fluorescence is the result of transition from orbit 139 to orbit 137.
Key words：Ponceau 4R;Molecule structure;Fluorescence spectroscopy;Density function theory
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