Structural and Optical Properties of Subporphyrinoids: A TD-DFT Study

Using ab initio approaches accounting for environmental effects, we investigate the ground- and excited-state properties of four subporphyrinoids: subporphyrin, subporphyrazine, tribenzosubporphyrin, and subphthalocyanine. We first show that the selected level of theory, that is DFT(PBE0), is able to reproduce the structure and NMR spectra of all compounds. The aromaticity of these four macrocyclic entities are next quantified and it is showed that these bowl-shape induced molecules present very strong aromatic characters. Next we analyze the spectral signatures of all four compounds using an approach going beyond the vertical approximation. The 0-0 energies are reproduced with a mean absolute deviation smaller than 0.1 eV, and the very good agreement obtained between experimental and theoretical band shapes allows us to unravel the vibronic contributions responsible to the specific band shapes of these subporphyrinoids. Finally, we investigate a large series of substituted subporphyrins, demonstrate the quality of the trends that are obtained with theory and design new compounds presenting red-shifted optical bands.