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

The absorption and the emission spectra of methanol and ethanol, scanned by the Edinburgh FLS920P steady-instantaneous fluorescence spectrometer, are studied on this paper. Aiming at comparison on the molecular structuresof methanol and ethanol under different states, we employ the density functional theory (DFT) and the single-excitation configuration interaction (CIS) to optimizemolecular structures 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, and investigate the effect caused by different exchange correlation functions on the calculated spectra. The results indicate that methanol and ethanol have weak absorption 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 from sigma* to pi*. 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 to study alcohols' molecular properties.