Theoretical investigation of the substituent effect on the electronic and optical properties of photochromic dithienylethene derivatives

We have studied the substituent effect on the optical properties of both the closed-ring and open-ring isomers of a series of dithienylethene photochromic molecules. We demonstrate that TDDFT method, in conjunction with moderate size basis set, provides an accurate tool for the determination of the lowest singlet excitation energies of dithienylethene compounds. We have seen that the absorption spectrum of both the closed-ring and open-ring isomers can be easily shifted to longer wave wavelengths by introducing (1) acetylenic groups at the 5-position of the thiophene rings and (2) electron-withdrawing substituents in the upper cyclopentene structure.