Abstract: Electrocyclic reaction mechanism of 2,3-diaryl maleic anhydrides was studied at B₃LYP/6-311+G(d,p)//HF/3-21Glevel.There are two reaction paths for the mechanism.One keeps all the species in trans forms with a strict C₂symmetry throughout the reaction path; and the other keeps all the species in cis forms with a strict C_s symmetry.The results are consistent with Woodward-Hoffman principle.The results also support the experimental result that the thermal irreversible property is improved when the hydrogen atoms on the central carbons involved in the bond forming process of the electrocyclic reaction are changed to methyl groups.There is less negative charge on central carbons involved in the electrocyclic reaction for 2,3-bis(2,4-dimethylthiophen-3-yl)maleic anhydride than for 2,3-bis(4-methylthiophen-3-yl)maleic anhydride, conforming the experimental result that the former compound is more stable to oxygen.The LUMO and HOMO energy gaps conform with experimental result that the maximum absorption wavelength for the closed-ring form of bis(methylthiophen-3-yl)maleic anhydride is longer than that of the open-ring form.

Key words: Density function calculation method, Diaryl maleic anhydrides, Photochromism