丹参酮分子结构及光谱性质的理论研究

Theoretical study on the structures and spectrum of Tanshinone

采用量子化学密度泛函理论(DFT)在B3LYP/6-31G*水平上对丹参酮Ⅰ、丹参酮ⅡA、隐丹参酮3个典型的丹参酮类化合物分子几何构型进行优化,分析分子前线轨道能级及分布特征。用含时密度泛函理论(TD-DFT)在相同水平对上述化合物分子进行电子吸收光谱研究。并且以乙醇为溶剂,计算其对分子结构和光谱性质的影响。计算结果表明:丹参酮Ⅰ分子骨架发生共轭形成大π键,为刚性的平面分子结构;丹参酮Ⅰ、丹参酮ⅡA、隐丹参酮分子共轭体系依次缩小。分子HOMO-LUMO能隙随着分子共轭体系的减少而增大。3个分子的λ_(max)均主要来源于电子的π→π*跃迁。乙醇对上述化合物分子结构和光谱性质有一定影响,吸收光谱均发生红移。同时还发现,乙醇改变了丹参酮Ⅰ的λ_(max)主要电子跃迁来源轨道。丹参酮Ⅰ在气相条件下λ_(max)主要来源于分子中的HOMO→LUMO+2的π→π*跃迁;而在乙醇中λ_(max)主要来源于HOMO-5→LUMO的π→π*跃迁,该跃迁存在明显的分子内电子转移现象。

To investigate the electronic structures, spectral properties and their relationship, tanshinone Ⅰ, tanshinone ⅡA and cryptotanshinone were optimized by using density functional theory （DFT） at the B3LYP/6-31G＊ level, the characteristics of the frontier molecular orbitals and the distribution of energy levels were analyzed. Time depended density function theory（TD-DFT） methods were employed to calculate spectral properties at the same level. The influence of ethanol solvent on the electronic structures and spectral properties was involved. It is found that Tanshinone Ⅰ is a planar structure, because there is a big π-π conjugation in this molecule. The order in the conjugated system is Tanshinone Ⅰ〉Tanshinone Ⅱ A 〉Cryptotanshinone, but the order in the energy barriers from HOMO to LUMO is opposite. The main absorption spectra originated from the π-π electronic transition. The ethanol may have an effect on the electronic structures, lead to UV spectra red shift and increase the λmax, It is also found that the ethanol may change the main orbital of the electronic transition of the λmax in tanshinone Ⅰ. The λmax in tanshinone Ⅰ is mainly from the π-π electronic transition of HOMO-→LUMO＋2 in gas, but mainly from the π-π electronic transition of HOMO-5→LUMO in ethanol, which has an intermolecular charge transfer. The λmax in tanshinone Ⅱ A and cryptotanshinone are mainly from the π-π electronic transition of HOMO→LUMO＋1 both in gas and ethanol.