Abstract:To study the changing relationship between the fingerprint characteristics of tangerine peel’s flavonoids in the terahertz band and their structural information, terahertz time-domain spectroscopy (THz-TDS) technique combined with density functional theory (DFT) was used for simulation and experimental analysis of the terahertz absorption spectra of the flavonoids in thetangerine peel. First, the terahertz absorption spectra of hesperidin, nobiletin and tangeretin in the 0.2~2.0 THz frequency band were obtained by using flavonoid compound tablet experiments. It was found that hesperidin exhibited two distinct characteristic absorption peaks at 1.63 and 1.89 THz. Nobiletin has four characteristic absorption peaks at 0.42, 0.66, 0.97 and 1.51 THz, tangeretin can observe three absorption peaks at 0.41, 0.53 and 1.03 THz. Then, the B3LYP hybrid functional method based on density functional theory used the 6-31G (d, p) and 6-311G (d, p) basis groups to analyze the hesperidin, nobiletin and tangeretin in the tangerine peel, and their terahertz vibrational spectra were simulated and calculated. The results showed that most of the absorption peaks of flavonoids came from the torsional vibration of their dihedral angles, and the highest proportion was 13.0%, 17.0% and 25.2%, respectively. This study reveals the response mechanism of terahertz characteristic peaks of flavonoids, which has important reference value for rapid detection of flavonoids in the tangerine peel by terahertz spectroscopy.
