Study on spectral properties of butyl hydroxytoluene: Experiment and theoretical calculation

Butylated Hydroxytoluene (BHT) is the most commonly used antioxidant in life. In this paper, based on density functional theory (DFT), the geometric properties and infrared spectra of BHT molecule were calculated at the PBEPBE /6-311G (d, p) level of theory. Then, based on time-dependent density functional theory (TD-DFT), combined with the PBEPBE/def2-TZVP level of theory, the first 30 excited states of the BHT molecule were calculated with absolute ethanol as the solvent. The results show that the theoretical and experimental spectra of BHT molecule are in good agreement on the whole. Due to the influence of the gas composition in the air, the experimental spectrum appears slightly red-shifted. The UV spectrum is mainly formed by the transition of the ground state S0 to the excited states S1, S2, S5, S6 and S7. According to the analysis of molecular orbital and electron-hole, the excitation types are local excitation and charge transfer excitation, among them, S0 → S1, S0 → S2 and S0 → S5 are mainly formed by n → π* and π → π* excitation, S0 → S6 and S0 → S7 are mainly formed by π → π* and n → 3pz excitation. In addition, BHT can remove superoxide groups from air by the O atoms on the phenolic hydroxyl group and the C atoms on the benzene ring. This study provides a theoretical reference for further understanding the structure and properties of BHT molecule and the detection of relevant antioxidants.