Ab initio calculations of fluorescence spectra have been scarcely reported in references.The fluorescence of three heterocyclic organic compounds with five-membered ring have been studied by B3LYP method of DFT

in this paper.Geometric configurations of three heterocyclic organic compounds are optimized by B3LYP method at the level of 6-31G

*

and there are no imaginary frequences in vibrational analyses.On this basis

the mechanics of electronic transition in these molecules has been discussed through molecular orbital analysis.The results show that the transition between HOMO and LUMO in the three compounds is the electronic transformation from C1

C2

C3 and C4 to hetero-atoms (N atom in pyrrole

O atom in furan and S atom in thiofuran).The fluorescence spectra of these three compounds have been calculated by CIS method at the level of 6-31G

*

.The results of calculation are essentially consistent with the experimental values.This paper should be valuable for ab initio calculation of electronic spectra of organic compounds.