基于密度泛函的甲醇和乙醇荧光特性研究

Studies of the Fluorescence Properties of Methanol and Ethanol Based on the Density Functional Theory

使用英国爱丁堡FLS920P荧光光谱仪,对甲醇、乙醇的紫外吸收光谱和荧光光谱进行实验检测,得到二者的光谱特征参数。分别采用密度泛函理论(DFT)和单激发组态相互作用(CIS)对二者分子的基态和激发态结构进行优化,并比较两种分子在不同能态下的差异。应用含时密度泛函理论(TD-DFT)的不同泛函结合极化连续介质模型(PCM)在6-31++G(d,p)水平上分别计算了二者的紫外吸收光谱和荧光光谱,与实验结果吻合。分析了甲醇、乙醇荧光产生机理,同时分析了不同泛函对于计算光谱的影响。结果表明:甲醇、乙醇在紫外波段有微弱吸收,在紫外激发下能产生拉曼峰和微弱的荧光峰。甲醇、乙醇的吸收光谱是由里德堡激发产生,产生荧光的轨道跃迁为σ~*→π~*。泛函OLYP能够较好地重现实验吸收能,而泛函MPWK能够较好地重现实验发射能,并且发现不同的纯泛函计算跃迁能也具有差异性。结果可为醇类分子的分子特性研究提供参考。

The absorption and the emission spectra of methanol and ethanol,scanned by theEdinburgh FLS920P steady-instantaneous fluorescence spectrometer,are studiedon this paper.Aiming at comparison on the molecular structuresof methanol andethanol under different states,we employ the density functional theory(DFT)and the single-excitation configuration interaction(CIS)to optimizemolecularstructures under the ground and excited state.The absorption and emission spectra of methanol and ethanol on the base of 6-31++G(d,p)are estimated based on the time-dependent density functional theory(TD-DFT)with the polarized continuous model(PCM),which are in agreements with the experimental results.Furthermore,we analyze the fluorescence mechanism of methanol and ethanol,andinvestigate the effect caused by different exchange correlation functions on the calculated spectra.The results indicate that methanol and ethanol have weakabsorption in ultraviolet regionand produce Raman band and weak fluorescence peaks through UV excitation.Meanwhile,the absorption spectra of methanol and ethanol are produced by Rydberg excitation,of which the orbit jumps fromσtoπ.Our results show that the OLYP function can reproduce the experimental absorption spectrum well and the MPWK function can predict the emission energy well.There exist differences on calculations of transition energy varying from different pure functions.Our results can provide a reliable tool tostudy alcohols'molecular properties.