亲脂性偶氮染料苏丹红Ⅲ(Sudan Red Ⅲ)分子因染色后可使食品鲜艳、 不褪色, 常被放入食品添加剂中, 食用后对人体的肝肾器官有明显的毒性作用, 严重影响人类身体健康。 苏丹红分子的毒性与其分子几何和电子结构密切相关, 对其结构、 电子激发等研究具有重要的指导意义。 采用密度泛函理论(DFT)方法结合def2-TZVP基组对苏丹红Ⅲ分子结构、 红外与拉曼光谱和紫外光谱进行系统研究, 结果表明PBE0和B3LYP杂化泛函方法计算的红外和拉曼光谱与实验值吻合; 采用含时的B3LYP杂化泛函计算得到的苏丹红Ⅲ分子的紫外-可见吸收峰为228、 353和490 nm, 与实验符合较好, 它们是基态电子向第2激发态、 第6激发态、 第30激发态跃迁所致。 采用空穴—电子分析法考察电子激发可知, S0→S2激发类型是氧、 氮原子到萘环和苯环上的n—π*电荷转移激发, 同时伴随着萘环、 苯环环内间的π—π*局域激发。 S0→S6激发类型是氮、 氧原子到萘环, 氮原子到苯环上的n—π*和萘环环内间π—π*电荷转移激发的叠加。 S0→S2和S0→S6激发类型属于电荷转移激发为主的混合激发。 S0→S30激发类型属于萘环环内的π—π*局域激发, 同时也伴随着氧、 氮原子到萘环上的n—π*和苯环到萘环上的π—π*电荷转移激发, S0→S30激发类型是以局域激发为主。 通过分子片段对空穴、 电子的贡献热图分析, 进一步证实了上述电子激发转移过程。 系统研究苏丹红Ⅲ分子的光谱及电子激发, 为实验检测食品苏丹红Ⅲ分子提供理论参考。

The lipophilic azo dye Sudan Red Ⅲ molecule enhances flavor or makes food bright and attractive. After eating, it has noticeable toxic effects on the liver and kidney organs of the human body and seriously affects human health. The toxicity of Sudan red molecule is closely related to its molecular geometry and electronic structure, which has important guiding significance for studying its structure and electronic excitation. In this work, we aimed to systematically investigate the molecular structure, infrared and Raman spectra, and ultraviolet spectra of Sudan Red Ⅲ by using the density functional theory (DFT) method in conjunction with the def2-TZVP basis set. The excitation properties of Sudan Red Ⅲ were also studied in detail by the hole-electron analysis method. The results show that the infrared and Raman spectra calculated for Sudan Red Ⅲ using the PBE0 and B3LYP exchange-correlation functional agree with the experimental data. Using the time-dependent B3LYP (TD-B3LYP) method with the def2-TZVP basis set, The UV-visible absorption peaks of Sudan Red Ⅲ show 228, 353, and 490 nm, which are in good agreement with the experiments. It can be found that they are through the transition of the ground state electrons to the second excited state, the sixth excited state, and the 30th excited state. The electron excitation characteristics are studied by using hole-electron analysis. It can be found that S0→S2 is attributed to the superposition of the n—π* charge-transfer excitation in the direction from oxygen and nitrogen atoms to the naphthalene and benzene ring, and the π—π* local excitation between intra-ring naphthalene and benzene rings. The superposition of the n—π* charge-transfer excitation from oxygen and nitrogen atoms to naphthalene and benzene ring and the π—π* local excitation between intra-ring naphthalene and benzene rings are excited by S0→S6. The electronic transition of S0→S2 and S0→S6 from the ground state to the excited state belongs charge transfer excitation, where the charge transfer excitation effect is dominant. S0→S30 is attributed to the superposition of local excitation and charge-transfer excitation, where the local excitation effect is dominant. They contributed π—π* local excitation between intra-ring naphthalene rings, and the superposition of n—π* in the direction from oxygen and nitrogen atoms to naphthalene and benzene ring and π—π* charge-transfer excitation between intra-ring naphthalene rings. Furthermore, we draw heatmaps of the contribution of molecular fragments to holes and electrons. The electron mentioned above excitation transfer was further confirmed by heat map analysis. The spectrum and electron excitation of Sudan Red Ⅲ were investigated systematically, which can provide a theoretical reference for experimental detection of Sudan Red Ⅲ in food.