Fig. 7. (Color online) Molecular structure and IR transmittance spectrum of PPO. The center of the figure displays the 3D structure of PPO, featuring a pentagonal oxazole ring (containing a red oxygen atom and a blue nitrogen atom) flanked by hexagonal phenyl groups. The red solid line represents the spectrum of PPO provided by SDBS, and the black line corresponds to the spectrum of our PPO powder sample. Additionally, the green solid line depicts the spectrum calculated using the B3LYP DFT method in Gaussian 16, aimed at comparing with the two experimental results. The stretching peak for the benzene ring's C-H bond appears around 3100 cm-1, with a slightly higher wavenumber nearby, representing the smaller stretching peak of the oxazole ring's C-H bond. Bending modes of the PPO molecule, including the C-N stretching mode, are present around 1500 cm-1, with lower wavenumber bending vibration modes evident around 700 cm-1. Additionally, peaks involving C-O stretching are observed around 1100, 1200, and 1300 cm-1.
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