1,4-苯二硫醇的表面增强拉曼光谱和激发态的密度泛函理论研究

Density Functional Theory Study of Surface-Enhanced Raman Spectra and Excited State of 1,4-Benzenedithiol

利用密度泛函理论(density functional theory,DFT)在B3LYP/6-311+g(d)(C,H,S)和Lanl2dz(Ag、Au)基组下对1,4-苯二硫醇分子及其复合物进行了结构优化和频率计算,得到了分子及其复合物稳定的化学构型和拉曼光谱。优化后的1,4-苯二硫醇分子的S—H键和苯环所在平面夹角为20.2°,分子非平面结构。模拟了金银团簇在苯硫醇分子表面的吸附行为,得到了金团簇和银团簇在分子表面的吸附方式,即,金团簇以接近平行的方向吸附于苯硫酚分子的表面而银团簇则以几乎垂直的方向吸附于分子表面。此外,还分析了静态极化率数值变化和自然键轨道(natural bond orbital,NBO)布局分析得到的电荷分布对拉曼光谱的强度变化的影响。复合物1,4-BDT-Au2,1,4-BDT-Ag2和三明治结构的Ag2-1,4-BDT-Au2拉曼光谱谱峰强度与静态极化率数值变化有很好的吻合。采用含时密度泛函理论(time dependent density functional theory,TDDFT)对Ag2-1,4-BDT-Au2复合物进行了激发态的分析计算,通过模拟吸收光谱和计算轨道跃迁单激发态,分析计算了三明治结构的电荷转移激发态,利用可视化的电荷转移,研究了表面增强拉曼(surface enhanced Raman scattering,SERS)化学增强机理。

Raman scattering spectra and optimized geometries of the 1 ,4-benzenedithiol molecule and complexes have been calcu-lated using density functional theory （DFT ） with B3LYP functional at the level of 6-311G＋ （d） basis set for C ,H ,S atoms and LanL2DZ for Ag ,Au atoms ,respectively .The optimized 1 ,4-benzenedithiol molecule was non-planar structure and the angle between benzene ring plane and S-H is 20 .20 .By means of the simulation of molecule adsorbed on gold and silver cluster ,we concluded that gold clusters are nearly parallel to the benzenedithiol molecule and silver clusters are almost perpendicular to the molecular surface .The authors studied the interaction between Raman intensity and molecular properties ,such as static polariz-ablity and charge distribution .The Raman intensity of 1 ,4-BDT-Au2 ,1 ,4-BDT-Ag2 and Ag2-1 ,4-BDT-Au2 were in good agree-ment with static polarizability .The excited states of Ag2-1 ,4-BDT-Au2 complex were calculated using time-dependent density functional theory （TDDFT） .And the simulated absorption spectra and several allowed singlet excited states were analyzed to in-vestigate the surface-enhanced Raman chemical enhancement mechanism .