Study Of The Electronic Spectra Of Coumarin And Its Derivatives

Coumarin and its deviating are a sort of important laser and fluorescence dyes, whichare widely used in the fields of electroluminescent material, organic photosensitingmaterial of solar battery and fluorescence probe used in the research of biology protein. Inthis thesis, a relatively high level theoretical investigation has been performed using thedensity functional theory (DFT) and time-dependent density functional theory (DFT)methods to calculate the bond length,bond angle,charge distribution and frontier orbitalenergy (HOMO and LUMO) of a sort of coumarin and its deviating, and I discussed therelationship between different substitute at 3,4,7-position of molecule and absorptionwavelengths.First, the structures of coumarin and its deviating have been carded out on Chem3D,and then are opted by PM3 of semi-empirical methods at the level of RHF (RestrictedHartree-Fock) without any restrict of symmetry. On the base, 5 methods of B3LYP/3-21G,B3LYP/6-31G,B3LYP/6-31G^*,B3LYP/6-31G^** and HF/6-31G^* are used to optimize thestructures and calculate the frequencies, the results show that the method of B3LYP/6-31G^*spent fewer time and better data.Then, the molecules are more calculated by Gaussian03. The method of B3LYP/6-31G^*is used to calculate quanta chemistry parameters—bond length, bond angle, chargedistribution and frontier orbital energy (E_HOMO,E_LUMO,ΔE) and electronic spectra. Theinfluence of different substitute at 3, 4, 7-position of molecule for geometry and electronicstructures is close to the experimental results. When electron-attracting group at 3, 4-position and electron-excluding group at 7-postion, conjugated effect of molecules isswell, the transition energy needs littler and wavelength is bath chromic shift.Third, the relationship between frontier molecular orbital and different substitute isdiscussed. The influence of different substitute at the different position for electronicspectrum and the relationship of absorption wavelengths and energy gap are also discussed.The curve of he absorption wavelengths and the state energy gapΔε, single electronicexcited energyΔE is linearity. Regression equation is also got, and the predicted result isnear to the calculated result.