Ab initio calculations of the colour of closed-ring diarylethenes: TD-DFT estimates for molecular switches

The visible absorption spectra of a series of diarylethene dyes have been evaluated by using a time-dependent density functional theory approach, explicitly taking into account bulk solvent effects. A complete basis set/functional methodological study has been performed. Using the PBE0 functional with the 6-311+G(2d,p) atomic basis set, we got a nice agreement between theoretical and experimental electronic transition energies for a 15 compound-set. The mean absolute error is limited to 0.13 eV and can further be reduced by a factor 4. On the contrary, the ZINDO//AM1 approach produces inconsistent absorption energies.