Structural, photophysical and theoretical studies of two dodecachlorinated porphyrins

Two dodecachlorinated porphyrins, 2,3,7,8,12,13,17,18-octachloro-5,10,15,20-tetra(4-chlorophenyl)porphyrin free base (TCl12PPH2) and its nickel compound (TCl12PPNi), have been synthesized. Single-crystal X-ray diffraction analysis shows that porphyrin rings are heavily distorted and exhibit saddled conformations. The Soret and Q bands of two compounds are red-shifted compared to their non-chlorinated counterparts. Theoretical calculations reveal that the optical band gap of TCl12PPH2 is reduced, whereas that of TCl12PPNi remains almost the same as to its non-chlorinated nickel compound due to the concurrent lowering of HOMO and LUMO energy levels. The frontier molecular orbitals are degenerated due to the decrease of symmetry of the molecules.

Chlorination of β-pyrrolic positions of porphyrin leads to distortion of the ring structure. The optical band gap of free base is reduced, whereas that of its nickel complex remains almost the same as to its non-chlorinated nickel compound due to the concurrent lowering of HOMO and LUMO energy levels. The frontier molecular orbitals are degenerated due to the decrease of symmetry of the molecules.Figure optionsDownload as PowerPoint slideHighlights
► Chlorination of β-pyrrolic position results in significant structure distortion of porphyrins.
► Chlorination leads to the red-shift of absorption maxima.
► The optical band gap of free base is reduced, whereas that of its nickel complex remains almost the same as to its non-chlorinated nickel compound.
► The frontier molecular orbitals are degenerated due to the decrease of symmetry of the porphyrin molecules.