Porphine core saddling: Effects on the HOMO/LUMO gap and the macrocycle bond lengths and bond angles

High level ab initio calculations on the saddle distortion of the porphine backbone with dihedral angles in the range 0–30° show the red shift of the Soret and Q bands of the aromatic macrocycle. Also, according to the optimized structure of the planar and saddle shaped porphine, the involvement of in-plane nuclear reorganization in the observed shifts of the bands upon the out-of-plane deformation of the porphyrin core especially to angles larger than 25° cannot be excluded. The distribution of electron density over the porphine frontier orbitals with D2h symmetry has been also studied.

Ab initio calculations reveal the red shifts of the Soret and Q bands of the conformationally constrained saddle shaped porphine with dihedral angles of 0–30°.Figure optionsDownload as PowerPoint slide