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A series of phosphorus(V) porphyrins functionalized with meso-phenyl, tolyl, or 4-methoxyphenyl groups and axial-ethoxy, trifluoroethoxy, or ethylene glycoxy groups have been synthesized and their spectroscopic, redox, and optical properties were investigated. The X-ray crystal structures revealed a significant saddling in porphyrin molecular structures due to the presence of a small P(+5) ion in the cavity. The absorption and fluorescence properties are less sensitive to the meso-functionality, with small redshifts observed when moving from phenyl to tolyl and then to 4-methoxyphenyl on the phosphorus(V) porphyrin. In contrast, the meso- and axial-functionalities significantly influenced the redox properties. Specifically, the meso-4-methoxy phenyl group lowered the oxidation potentials, while the axial trifluoroethoxy units reduced the reduction potentials. This study demonstrates that by carefully choosing the axial and meso-substitutions, it is possible to selectively tune the redox potentials with minimal impact on optical properties. Steady-state and time-resolved measurements revealed relatively high fluorescence quantum yields, with lifetimes ranging from 2 to 4 ns. Together, the high fluorescence quantum yields and tunable redox potentials suggest that the investigated porphyrins could serve as excellent photosensitizers in model compounds for artificial photosynthesis and molecular electronic and photonic devices.

Soret-excited resonance Raman (RR) spectra are reported for some 40 nonplanar metalloporphyrin complexes. These include (i) copper β-octabromo-meso-tetra(para-X-phenyl)porphyrins, Cu[Br₈T(p-X-P)P] (X = CH₃, H, F, CF₃, NO₂); (ii) copper β-octachloro-meso-tetra(para-X-phenyl)porphyrins, Cu[Cl₈T(p-X-P)P] (X = H, CF₃); (iii) zinc β-octabromo-meso-tetraphenylporphyrin, Zn[Br₈TPP], and zinc β-octasubstituted meso-tetrakis(pentafluorophenyl)porphyrins, Zn[Y₈TPFPP] (Y = CH₃, Cl, Br); (iv) nickel β-octabromo-meso-tetra(para-X-phenyl)porphyrins, Ni[Br₈T(p-X-P)P] (X = CH₃, H, F, Br, COOMe, CF₃, NO₂), with and without bis-ligated axial pyridine and imidazole ligands; (v) nickel β-octachloro-meso-tetra(para-X-phenyl)porphyrins, Ni[Cl₈T(p-X-P)P] (X = CH₃, H, F, COOMe, CF₃, NO₂), again with and without bis-ligated axial pyridine ligands; and (vi) nickel octaethyltetraphenylporphyrin, Ni[OETPP], and palladium octaethyltetraphenylporphyrin, Pd[OETPP]. The spectra lead to the following conclusions. For a particular nonplanar porphyrin ligand, the high-frequency RR marker bands ν₂ and ν₄ downshift with increasing size of the coordinated metal ion, including a low- to high-spin transition for nickel porphyrins. In contrast, for a particular coordinated metal ion, these frequencies downshift with increasing nonplanarity of the porphyrin ligand, which in turn correlates with decreasing metal–nitrogen distances or the 'core size'. Similar results were also found for β-octaalkyl-meso-tetraphenylmetalloporphyrins by Shelnutt and coworkers. Thus, it appears that this complicated multiple-valued core size dependence of the high-frequency RR marker bands may be a generally shared property of all saddled metalloporphyrins. Variations in the electronic character of the metalloporphyrins resulting from variations in the para-substituents on meso-aryl groups do not result in significant shifts in the RR marker bands. The symmetric C_meso–C_phenyl stretching frequency (ν₁) at approximately 1240 cm^-1 is prominent in all the RR spectra except those of the low-spin Ni saddled porphyrins, for which they are relatively suppressed, and possible electronic-structural implications of this effect are discussed. In the low-frequency regions of the RR spectra of the compounds studied, the strongest band is roughly around 300 cm^-1 and appears to be relatively safely assignable as γ₁₆, a pyrrole tilting mode that strongly resembles the saddling mode in terms of atomic displacements.