苋菜红分子基态和激发态结构与光谱性质的量子化学研究

Quantum-chemical studies on the ground and excited state molecular structures and spectral properties of amaranth

应用英国Edinburgh FLS920P光谱仪对苋菜红的吸收光谱和荧光光谱进行了实验检测.同时,分别采用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)对苋菜红分子的基态和激发态构型进行优化,经振动分析合理后,比较这两种能态下分子结构的差异,并对其前线分子轨道和发光机制进行了分析.在此基础上,选用6种泛函并结合溶剂化模型(PCM)在6-311++G(d,p)水平上分别计算苋菜红的吸收光谱和荧光光谱.计算结果表明:苋菜红含有分子内氢键,基态结构非平面,两个萘环所在平面有一定的夹角,激发态时两个萘环共平面;CAM-B3LYP泛函得到光谱的理论值与实验结果基本吻合;421 nm处的荧光峰值波长对应的轨道跃迁为LUMO→HOMO-1.

Abstract： The Edinburgh FLS920P spectrometer was applied on the detection of the absorption and the emission spectra of amaranth. Then, the density functional theory （DFT） and time -dependent density functional theory （TD- DFT） were used on the optimization of amaranth under the ground and the excited state, respectively. The molecule structures of the two states were compared, and the frontier molecular orbits, the mechanisms of absorption and emission were studied after the vibration analysis. On the basic of the optimized geometry struc- tures, six functions combined the continuum solvation model （PCM） on the 6 - 311 ＋ ＋ G （ d, p） level were used to calculate the absorption and the emission spectra. The results show that the hydrogen bond exists in the amaranth, the geometry structure on the ground state is non - planar, and there are angles between the two planes of the naphthalene rings, and the geometry structure on the excited state is nearly planar. The results of calculations are basically consistent with the experiments. The orbit transition of fluorescence peak wavelength 421 nm corresponds to the transition of LUMO--~HOMO - 1. Key words： Amaranth ; Time - dependent density functional theory （TD - DFT） ; Quantum chemistry ; Absorp- tion spectrum; Fluorescence spectrum