Narrow Results

Lewis acid catalyzed condensation of pyrrole and 4-fluoro-2,6-dimethylbenzaldehyde followed by chemical oxidation afforded the corresponding chlorin along with the parent porphyrin. The subsequent metalation of the porphyrin-chlorin mixture in the presence of Zn(OAc)₂·2H₂O afforded Zn mono and di-hydroxychlorins in addition to the Zn porphyrin in a one-flask synthesis. This new direct hydroxylation reaction eliminates the need for highly toxic OsO₄ and H₂S that are traditionally used for the generation of hydroxy chlorins. In addition to the full characterization of the zinc chlorins, we present cyclic voltammograms, steady-state absorption, and emission profiles of this rarely available class of compounds. Our findings show that Zn mono- and di-hydroxychlorins are stable compounds that possess exceptionally long triplet excited states in solution, making them promising candidates for photodynamic therapy.

The preparation and luminescence properties of a dipalladium cofacial porphyrin dimer (DPA)Pd₂ (where DPA is the tetraanion of 1,8-bis(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrin-5-yl)anthracene) are reported and compared together with the photophysical behavior of the known monomeric (OEP)Pd and (TPP)Pd complexes. The effect of dioxygen in the presence and in the absence of the very bulky base, 1-t-butyl-5-phenylimidazole, is also investigated. The title dimer, (DPA)Pd₂, shows fluorescence and phosphorescence in the ps and ms time scale, respectively, with a global intensity lower than that of the porphyrin monomer analogues. The fluorescence sensitivity towards dioxygen quenching appears greater for the dipalladium complex than that of the monoporphyrin derivatives. In the presence of the bulky base, this sensitivity shows a dramatic decrease.

The crystal structures of two face-to-face diporphyrin compounds based upon the DPA ligand (1,8-bis(5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethyl-porphyrinyl))anthracene), i.e. H₄(DPA) and (DPA)Co₂ are reported. The structural data are compared to that of other bimetallic DPA systems, and diporphyrinic Co complexes. In addition, the luminescence properties of (OEP)Co (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrin), H₂(DPA)Co, H₂(DPA)(CoIm)O₂, (DPA)Co₂, (DPA)(CoIm)₂O₂ are reported, where Im is 1-t-butyl-5-phenyl imidazole. Contrary to previous literature reports, the Co(II) species are found to be weakly luminescent, where fluorescence is detected for both the mono- and diporphyrinic systems, and is assigned to emissions arising from the lowest ¹Q(ππ*) states, while phosphorescence is detected at 77 K only for the monoporphyrin species, (OEP)Co. On the other hand, the Co(III) complexes are not luminescent.

The synthesis and photochemical characterization of a covalently bonded palladium meso-sulfophenylporphyrin-poly(vinyl alcohol)polymer (PVA-PdTPPS), made via reaction of the chlorosulfonyl derivative of Pdmeso-tetrakis-phenylporphyrin with the alcohol group of the polymer to form the sulfonate ester, is described. Absorption, emission and phosphorescence lifetime data are reported. In both the solid film and in aqueous solution phosphorescence decays in the absence of oxygen are non-monoexponential and suggest heterogeneity in the decay and oxygen quenching kinetics. As a solid film there is very little phosphorescence quenching by oxygen at moderate pressures of O₂ (0-30 Torr), but in aqueous solution oxygen quenches at a rate of 7.5 (±0.5) × 10⁸M.s⁻¹. The synthetic route described is versatile enough to be used with a variety of metalloporphyrins and polymers and this allows the possibility of extensive tuning in terms of lumophore lifetime, polarity, solubility, location in heterogeneous media, and compatibility with other polymers.