Theoretical Study On The Photochromic Properties Of Organic Optical Storage Materials Diarylethene Derivatives

Photochromism has attracted considerable attention because of its potential application to molecular devices, such as optical memories and switches. With organic photochromic materials, reading and writing of information are accomplished in all-photon mode. Diarylethene derivatives are the most promising compounds because of their fatigue resistant and thermally irreversible properties. The photochromic reaction is based on a reversible transformation between the open-ring isomer, with a hexatriene structure, and the closed-ring isomer, with a cyclohexadiene structure, according to the Woodward-Hoffmann rule. Most diarylethenes show very large spectral shifts upon photoisomerization from the open- to the closed-ring isomers(>6500cm-1). While the open-ring isomer is colorless in most cases, the closed-ring isomer has a color of yellow, red, or blue, depending on the molecular structure.Diarylethene derivatives were first introduced as photochromic compounds in late 1980's. Since then a number of 1,2-bisaryl-substituted maleic anhydride, maleimide, cyclopentene and perfluorocyclopentene moieties have been employed. Each bridging unit has its advantages and disadvantages. In chapter 3, we have systemically investigated the photochromic properties of different dithienylethene derivatives with different bridging units. The calculated results indicate that all selected open-ring dithienylethene isomers with various bridging units can arise photochromic cyclization due to the close distance (～3.700?) between two reactive carbons and symmetrical molecular structure. In the photocyclization reaction the change of molecular dipole moment is mostly dependent on the nature of the bridging moiety rather than the redistribution of electron density. In most cases, the frontier MOs are mainly located on the central fragment which undergoes major changes in photochromic process for both the open- and closed-ring forms. Comparing with closed-ring isomers, the open-ring forms hold bigger frontier MOs energy gap which was more affected by heavy atoms composing the bridging unit. In virtue of time-dependent density functional theory, the electronic absorption wavelengths of the closed-ring isomers were well reproduced comparing with experimental results. The calculations show that the first singlet excited state...