One-flask synthesis of meso-substituted dipyrromethanes and their application in the synthesis of trans-substituted porphyrin building blocks

From mononuclear to polynuclear macrocyclic or macroacyclic complexes

Light-harvesting arrays containing one, two, or eight boron-dipyrrin (BDPY) pigments and one porphyrin (free base or Zn chelate) have been synthesized using a modular building block approach. The reaction of pyrrole and 4-(BDPY)benzaldehyde or 3,5-bis(BDPY)benzaldehyde, prepared by Pd-mediated ethynylation with the corresponding iodo-benzaldehydes, affords the desired BDPY-porphyrin array in yields of 10−58%. The arrays are soluble in organic solvents and have been characterized by static and time-resolved absorption and fluorescence spectroscopy. The blue-green BDPY absorption complements spectral coverage of the porphyrin chromophores and rivals the intensity of the porphyrin Soret band when eight BDPY accessory pigments are present. Efficient energy transfer from the BDPY pigment(s) to the porphyrin (free base or Zn-chelate) is observed in arrays containing one or two (>90%) or eight (>85%) accessory pigments per porphyrin. Biphasic excited-state decay behavior is exhibited by the BDPY pigments in isol...

http://chembio.uconn.edu/Group_pubs/1995-1999/li_1998_jacs.pdf

Design, Synthesis, and Photodynamics of Light-Harvesting Arrays Comprised of a Porphyrin and One, Two, or Eight Boron-Dipyrrin Accessory Pigments

Synthetic routes to multiporphyrin arrays.

A model photosynthetic antenna consisting of four covalently linked zinc tetraarylporphyrins, (PZP)3−PZC, has been joined to a free base porphyrin-fullerene artificial photosynthetic reaction center, P−C60, to form a (PZP)3−PZC−PC60 hexad. As revealed by time-resolved absorption and emission studies, excitation of any peripheral zinc porphyrin moiety (PZP) in 2-methyltetrahydrofuran solution is followed by singlet−singlet energy transfer to the central zinc porphyrin to give (PZP)3−1PZC−P−C60 with a time constant of ∼50 ps. The excitation is passed on to the free base porphyrin in 240 ps to produce (PZP)3−PZC−1P−C60, which decays by electron transfer to the fullerene with a time constant of 3 ps. The (PZP)3−PZC−P•+−C60•- charge-separated state thus formed has a lifetime of 1330 ps, and is generated with a quantum yield of 0.70 based on light absorbed by the zinc porphyrin antenna. The complex thus mimics the basic functions of natural photosynthetic antenna systems and reaction center complexes.

An Artificial Photosynthetic Antenna-Reaction Center Complex

An improved synthesis of 5,15-diaryloctaalkylporphyrins

Strapped porphyrins were prepared directly by the acid-catalyzed condensation reaction of 3,3′-diethyl-4,4′-dimethyl-2,2′-dipyrrylmethane and methylenedioxy bridged dialdehydes having a strap linkage longer than 7 atoms. Dimeric and trimeric porphyrins with coplanar and orthogonal (T-shape) geometries were also synthesized in good yields as an application of this method. In the strapped porphyrins, the distortion of porphyrin ring increases systematically on shortening the strap linkage, which is confirmed by their 1H NMR data, red shifted absorption, and fluorescence spectra. In the coplanar dimeric and trimeric porphyrins, the electronic interactions between the porphyrins were distinctly observed, while in the orthogonal “T-shaped” dimers and “H-shaped” trimers, appreciable electronic interactions were not observed.

Synthesis of strapped, dimeric, and trimeric porphyrins based on intramolecular macrocyclization reactions

Long-lived charge separated states from distance fixed triads consisting of zinc porphyrin, free-base porphyrin, and pyromellitimide

Geometry- and solvent-polarity-dependent photoinduced electron transfer in conformationally restricted magnesium—free-base hybrid diporphyrins

Reversible Schiff base condensation of bis(salicylaldehyde)-linked porphyrins and ethylenediamine under high dilution gave salen-capped porphyrins in high yields Site selective insertion of nickel(II) into the salen and zinc(II) into the porphyrin gave the corresponding Ni–Zn heterobinuclear complexes The geometrical relationship between the two metal centers was estimated by 1H NMR spectroscopy The porphyrin π electronic state of these Ni-salen-capped Zn-porphyrins was perturbed by their Ni-salen cap, which was studied by 400 MHz 1H NMR, UV-Vis spectra, fluorescence, and cyclic voltammetry measurements

Fumikazu Kobayashi

Papers

An improved synthesis of 5,15-diaryloctaalkylporphyrins

Synthesis of strapped, dimeric, and trimeric porphyrins based on intramolecular macrocyclization reactions

Long-lived charge separated states from distance fixed triads consisting of zinc porphyrin, free-base porphyrin, and pyromellitimide

Geometry- and solvent-polarity-dependent photoinduced electron transfer in conformationally restricted magnesium—free-base hybrid diporphyrins

Salen-Capped Porphyrins as an Active Site Model of Metalloenzymes: Synthesis and Their Intramolecular Interactions between the Metal Complexes