Application of MCD Spectroscopy and TD−DFT to a Highly Non-Planar Porphyrinoid Ring System. New Insights on Red−Shifted Porphyrinoid Spectral Bands

Abstract

The first magnetic circular dichroism (MCD) spectra are reported for tetraphenyltetraacenaphthoporphyrin (TPTANP). The impact on the electronic structure of steric interactions between the fused acenaphthalene rings and the meso-tetraphenyl substituents is explored based on an analysis of the optical spectra of the Zn(II) complex (ZnTPTANP) and the free base dication species ([H4TPTANP]2+). In the case of ZnTPTANP, significant folding of the porphyrinoid ligand induces a highly unusual MCD-sign reversal providing the first direct spectroscopic evidence of ligand nonplanarity. Density functional theory (DFT) geometry optimizations for a wide range of Zn(II) porphyrinoids based on the B3LYP functional and TD-DFT calculations of the associated UV-visible absorption spectra are reported, allowing a complete assessment of the MCD data. TPTANP complexes are found to fall into a class of cyclic polyenes, termed as soft MCD chromophores by Michl (J. Pure Appl. Chem. 1980, 52, 1549.), since the signs of the Faraday A1 terms observed in the MCD spectrum are highly sensitive to slight structural changes. The origin of an unusually large red shift of the main B (or Soret) band of MTPTANP (the most red shifted ever reported for fused-ring-expanded metal porphines) and of similar red shifts observed in the spectra of other peripherally crowded porphyrinoid complexes is also explored and explained on this basis.

Ground and excited states of zinc phthalocyanine, zinc tetrabenzoporphyrin, and azaporphyrin analogs using DFT and TDDFT with Franck-Condon analysis

“…28 In fact, there is a large amount of investigation of MPcs over the last couple of decades by Mack, Stillman, and Kobayashi. 19,20,[28][29][30] However, there has been minimal research presented on these molecules using Franck-Condon analysis until a recent study by Gou et al presented work on ZnPc and ZnTBP. 27 Two approaches seem to have dominated the theoretical work.…”

Spectroscopic investigations and theoretical calculations of DABCO induced xanthene bridged self-assembled zinc(II) porphyrin dimer

“…The MCD spectra of 5 are similar to those of ZnTPP [18] (Fig. 5), since the relative energies of the frontier p-MOs are very similar both in the presence and absence of DABCO (1.0 eq.).…”

TD-DFT calculations and MCD spectroscopy of porphyrin and phthalocyanine analogues: rational design of photosensitizers for PDT and NIR region sensor applications

“…In 2005, Mack et al 15 reported an analysis of trends predicted in DFT and TD-DFT calculations of 17 radially symmetric zinc porphyrinoids, which included several fused-ring-expanded Pc complexes, that were carried out with the B3LYP functional. The closed shell d 10 configuration of the Zn(II) ion was selected since it results in a complete absence of metal to ligand and ligand to metal charge transfer bands above 300 nm, so that trends in the energies of the main π → π * transitions can be readily compared.…”

“…15 Series of tetraazaporphyrins with peripheral pyrazine (13)(14)(15)(16)(17) and benzopyrazine (18-22) moieties were also studied.…”