Benchmarking computational methods and influence of guest conformation on chirogenesis in zinc porphyrin complexes

Circular dichroism (CD) is a convenient and widely used tool for investigating structures of chiral molecules. However, the unambiguous simulation of CD spectra is not a trivial task, because the accuracy of theoretical calculations depends on the nature of the system. In the present work, the induced CD spectra of six zinc porphyrin complexes with chiral guests were simulated by using different DFT methods. The best agreement between theoretical and experimental results for the Soret (B) band absorption region was achieved with the ωB97X-D, CAM-B3LYP, and M06-2X functionals with implicit inclusion of solvent effects (SMD model). Also, a good correlation between the simulated and experimental spectra was obtained with the DZVP basis sets, however a more accurate simulation of the length- and velocity rotational strengths needed larger TZVP basis sets. Additionally, the conformation of the chiral guest influences the chirogenic mechanism.