[Quantum chemistry study on fluorescence spectra of three aromatic hydrocarbons].

In the present paper, the fluorescence spectra of three common pesticides, isoprocarb, metolcarb and pirimicarb, were theoretically studied. The geometries of these compounds were fully optimized by density function theory (DFT) method at the B3LYP/6-31+G level. The three compounds under study were confirmed as true minima on the potential energy surface in the presence of only real frequencies by the vibrational analysis. The fluorescence spectra were calculated by configuration interaction (CI) method with PCM model, and the results match with the experimental values. The results of calculation suggest that the three compounds with planar structures are hyperconjugation systems. By the addition of the donor-electron groups, the wavelengths of the fluorescence spectra increased, and the frequencies underwent red-shift. In addition, the substitute alkyl has no more influence on the fluorescence spectra, but the addition of amido groups has more influence on the fluorescence spectra.