A DFT study of the low-lying singlet excited states of the all-trans peridinin in vacuo

The electronic properties of peridinin (Per) are investigated using density functional theory (DFT) with a time dependent (TD) treatment for transitions from the ground state to the low-lying electronic excited states. The use of a TD-DFT approach was first tested on the simpler beta-carotene molecule in order to see the performances of different functionals. It turns out from the present study that a TD-DFT approach provides a rather good qualitative picture for the electronic properties of this system for which the use of highly correlated ab initio methods with the needed prescriptions, for example, a large enough basis set and/or active space, is still prevented by its large dimension. The vertical transitions of Per obtained in vacuo using TD-DFT are in good agreement with experimental data available in a nonpolar solvent like n-hexane. Vertical energies obtained for the minimum energy structure of Per were also refined, spanning the Per in vacuo conformational space using ab initio molecular dynamics on its ground state hypersurface. These calculations also confirm the reliability of TD-DFT calculations at least on properties available from a dynamical sampling, that is, possible state inversion and partial explanation of bandwidth. Hence, combining these results with TD-DFT calculations, it is possible to better understand some spectroscopic properties of peridinin.