TD-DFT investigation of diarylethene dyes with cyclopentene, dihydrothiophene, and dihydropyrrole bridges.

We have investigated the visible spectra of closed-ring diarylethenes presenting cyclopentene, dihydrothiophene, and dihydropyrrole bridging structures. Our simulations have been performed with an ab initio time-dependent density functional theory approach that takes into account bulk environmental effects. The computed lambda(max) agree qualitatively with experiment, and once a simple statistical treatment is performed, a quantitative agreement is reached. Indeed, after linear fitting correction, the mean absolute error is limited to 6 nm or 0.03 eV for the 57 diarylethenes considered. To unravel the most important parameters for this photochromic class, several structural parameters are correlated to the UV/vis spectra. It turns out that the bond length alternation in the chromogenic unit allows a fast and accurate prediction of the color of these dyes. In addition, we compare our results to available electrochemical data.