Theoretical Study On The Spectrum Properties Of Flavonoid Compounds

Flavonoid compounds have become one of fascinating areas of researches in recent years. In the paper, the 13C-NMR of the series of flavonol and isoflavone compounds have been studied by the quantum-chemical calculation program GAUSSIAN98 at the level of 6-31G; Besides, the fluorescence spectra of the series of flavone,flavonol and aurone compounds have been studied by CIS method with ideal gas model and PCM model respectively.We choose flavonol compounds with hydroxyl substituents on B ring and isoflavone compounds with hydroxyl substituents on A ring to study their 13C-NMR properties .Firstly the geometric configurations have been optimized and vibrational analyses have been preformed to confirm at the level of B3LYP/6-31G. The IR spectrum data of compounds are essentially consistent with experimental values. Secondly, the 13C-NMR spectra have been calculated by GIAO method at the level of B3LYP/6-31G and the relative errors are in the acceptable scale.We optimized the geometric configurations of the series of flavone compounds by ab initio B3LYP method with 6-31G basis set and confirmed the stable geometries by vibrational analyses. Then we calculated the fluorescence spectra with CIS method provided by GAUSSION98 program at the different levels with gas model and PCM model respectively. The results show that it is important to choose a proper basis set to calculate the fluorescence spectra for the series of flavone compounds. Because the results show that with gas model, the results of calculation are essentially consistent with experimental values at the B3LYP/6-31+G level and B3LYP/6-311G level by using CIS method. And with PCM model, the results of calculation are essentially consistent with experimental values at the B3LYP/6-311G level.In addition, we calculated the fluorescence spectra of the series of flavanone and aurone compounds .The series of flavanone compounds have lower planar property. We studied the substituent effect by calculating their fluorescence spectra. The results show that: for the ideal gas model ,when the compounds have the same geometry on A and C rings, increasing hydroxyl substituents on B ring has a little influence on the compound. But when adding hydroxyl substituent to the C5 on A ring , it has a greater influence on the compound than on B ring . For PCM model the fluorescence spectra have a simple trendency with the gas model. Then we calculated the fluorescence spectra of the series of aurone compounds at the level of B3LYP/6-311G by using CIS method. The results show that: the position and the number of the hydroxyl substituents have a little influence on the compounds, the fluorescence spectra of the series of aurone compounds are determined to their own geometry . The aurone compounds are generally on one plane ,and they have a bigger conjugate system . The inducement of hydroxyl substituents has little influence on their own geometries . The results of calculation are essentially consistent with experimental values .The above-mentioned calculated results show that: the calculation of the 13C-NMR spectra and the fluorescence spectra of flavonoid compounds by the quantum-chemical calculation programs is feasible. At the same time, we can also discuss the transition of electrons and the effect of substitute groups. This paper will put forward some useful reference for theoretical and experimental researches.