In this paper, semi-empirical method AM1 is used to study the relationship between structures and photochromic properties of fulgides. Structures of six kinds of fulgides were optimized. The calculated ground state equilibrium structure of 1E was compared with that of experiment - a and the quantum chemical calculation results of others. Our result indicated that the first singlet excited structures of unclosed and closed fulgides were more similar to eachothe than their ground states, which explained why fulgides were both thermostable and photochromic. The trend of the quantum yield of ring opening (Φ~C~E) is in agreement with that of bond order of C(10) -C(15) of closure structures of fulgides. However, the quantum yield of ring closure (Φ~E~C) cannot be interpreted simply in terms of the distance and bond order of C(10)-C(15). Regarding unclosed fulgides, the reason for the shorter distance between C(10)-C(15) in excited state than that in ground state is believed to be the torsion interaction between furan group and R^2. Additionally, carbon atomic net charges of 1E can be used to explain its ^1^3C NMR data.

Key words: PHOTOCHROMISM