Using a time-dependent density functional approach and taking into account the bulk solvent effects, we study the modification of the optical properties of maleic anhydride diarylethenes induced by structural changes. Our results reproduce the auxochromic shifts described by experiments. We show that the closed forms of diarylethene molecules are much more sensitive to heteroatom substitution of the cyclopentadienyl rings than the open forms. The addition of electro-active groups to the reactive carbon atoms is also investigated. The major effect on the UV/visible spectra originates from the resonance effect as measured by the Hammett’s factor.