Slipped Cofacial Dimer Research Articles

Stacked Pairing of Anionic Porphyrins on a Tetracationic Macrocyclic Template

Dimers of dianionic porphyrins were formed via template-directed self-assembly on a tetracationic macrocycle. Single-crystal X-ray structural analyses revealed that [5,10-bis(4-sulfonatophenyl)-15,20-diphenylporphyrinato]nickel(II) (Ni(II)TPPS2A2−) or [5,15-bis(4-sulfonatophenyl)-15,20-diphenylporphyrinato]nickel(II) (Ni(II)TPPS2O2−) formed discrete J-type slipped cofacial dimers, which are structural analogues of a typical natural cofacial porphyrin dimer, on the tetracationic template in the crystals.

The formation of a slipped cofacial dimer of zinc (II) tripyridylporphyrin in water-soluble polymer

A novel tripyridylporphyrin monomer, 5-[4-[2-(acryloyloxy)ethoxy]phenyl]-10,15,20-tris(4-pyridyl)porphyrin (TrPyP), and its zinc (II) complex (ZnTrPyP) were synthesized. It was copolymerized with acrylamide to prepare water-soluble polymer P(ZnTrPyP-AM). The aggregation behavior of P(ZnTrPyP-AM) in aqueous solution was investigated by UV–visible absorption spectra. The red shift of Q band and the significantly enhanced relative intensity ( ɛ α / ɛ β ) indicated that the ZnTrPyP was axially coordinated. Meanwhile, Soret band of porphyrin split into two bands, suggesting exciton coupling of aggregates. The porphyrin pendants of P(ZnTrPyP-AM) were supposed to form a slipped cofacial dimer and the macromolecular matrix helped to create the well-defined porphyrin aggregates. This finding was helpful for the assembly of artificial light-harvesting systems in aquatic environment to mimic the dimeric structure in natural LHC.

Water-soluble supramolecular porphyrin dimer: self-organization of mono(imidazolyl)-substituted Zn porphyrin to a special-pair type dimer in water

Abstract Tris(4-carboxylphenyl)-mono( N -methylimidazolyl)-substituted Zn porphyrin was synthesized as a precursor for a water-soluble supramolecular porphyrin dimer. The dimer formation was performed in a NaHCO 3 aq solution (pH 8.4) and phosphate buffer solutions (pH 7.4–9.0). The split Soret bands of Zn porphyrin observed in the absorption spectra clearly showed self-organization to a special-pair type slipped cofacial dimer via metal coordination of imidazole even in water.

Synthesis of galactosylated zinc bacteriochlorophyll- d analogs and their self-aggregation in an aqueous methanol solution

Chlorophyll derivatives possessing a galactosyl moiety at the 17-substituent were prepared by condensation of a carboxy group in the 17-substituent of chlorin chromophores with an amino group on the galactosides having four unprotected hydroxy moieties. Synthetic zinc 3-hydroxymethyl-13 1-oxo-chlorins covalently linked with the galactosyl group through a spacer of various lengths self-aggregated in an aqueous methanol solution to give a slipped cofacial dimer and large oligomers with a red-shifted Q y absorption band. The resulting oligomers were similar to J-aggregates of bacteriochlorophyll- d in main light-harvesting antennas of green photosynthetic bacteria. Electronic absorption spectral analyses of the hydrophilic chlorophyll derivatives in the aqueous solution indicated that their self-aggregation was dependent on the spacer; the shorter afforded their dimers predominantly and the longer disturbed the formation of chlorosomal large oligomers.

Synthesis of Chiral Porphyrins through Pd‐Catalyzed [3+2] Annulation and Heterochiral Self‐Assembly

Positive discrimination: Palladium-catalyzed [3+2] annulation of meso-bromoporphyrin with norbornene derivatives efficiently provides novel chiral meso,β-fused porphyrins with a rigid structure (as shown). A chiral benzoazanorbornene-fused zinc porphyrin assembles selectively to form the slipped cofacial dimer in a heterochiral association, which allows construction of a heterodimer from two porphyrin components through chiral discrimination. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2008/z801269_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Dimeric Assemblies from 1,2,3-Triazole-Appended Zn(II) Porphyrins with Control of NH-Tautomerism in 1,2,3-Triazole

Cu(I)-catalyzed 1,3-dipolar cycloaddition of meso-ethynyl Zn(II) porphyrin with benzyl azide efficiently provides meso-1-benzyl-1H-1,2,3-triazolyl Zn(II) porphyrin, which assembles to form a slipped cofacial dimer by the complementary coordination of the triazole nitrogen atom at the 3-position to the zinc center of a second porphyrin moiety both in the solid and solution states. Removal of the benzyl protection and introduction of a 2-ethoxycarbonylphenyl moiety greatly stabilize the dimeric assembly through an additional hydrogen bonding interaction between the NH proton of 2H-1,2,3-triazole and the carbonyl oxygen.

Synthesis of meso-5-Azaindolyl-Appended Zn(II) Porphyrins via Pd-Catalyzed Annulation

Pd-catalyzed annulation reaction of meso-hexynyl Zn(II) porphyrin with 4-amino-3-iodopyridine efficiently provides meso-3-(5-azaindolyl)-substituted Zn(II) porphyrin as a major product, which assembles to form a slipped cofacial dimer by the complementary coordination of the pyridine moiety to the Zn(II) center. 2-iodoaniline and 2-iodophenol also undergo this [3 + 2] annulation with the meso-hexynyl Zn(II) porphyrin to furnish meso-indolyl- and benzofuranyl-substituted Zn(II) porphyrins, respectively.

Role of the Special Pair in the Charge‐Separating Event in Photosynthesis

We synthesized special-pair/electron-acceptor systems consisting of a complementary slipped cofacial dimer of imidazolyl-substituted zinc porphyrin, bearing pyromellitdiimide as the electron acceptor. In the case of the dimer, the first and second oxidation potentials were split into a total of four peaks in the differential pulse voltammetry measurement. Furthermore, the shift values of the first oxidation potentials obtained by changing the solvent polarity for the dimer were almost half of those observed for the monomer. These results indicate that the radical cation is delocalized over the whole pi system of the dimer. Time-resolved transient absorption measurements revealed that, relative to the corresponding monomer, the dimer accelerated the charge separation rate, but decelerated the charge recombination rate. The smaller reorganization energy of the slipped cofacial dimer relative to that of the monomeric system demonstrates the significance of the special-pair arrangement for efficient charge separation in photosynthesis.

Dimeric aggregates of five-coordinated methyl(phthalocyaninato)Rh(III): 1H NMR evidence for staggered and slipped cofacial dimers

The 1 H NMR spectra of the five-coordinated rhodium phthalocyanine complex Me ( RPc ) Rh (III) (1, RPc = dianion of 1,4,8,11,15,18,22,25-octa-n-pentylphthalocyanine) in toluene indicate that it exists as a discrete monomer at low concentrations. The complex forms a dimer aggregate reversibly in the concentration range of 2.6–10.2 mM at -90 < T < 22 ° C . The dimerization constants at -60, -80, and -90 °C are 2.0 × 102, 5.7 × 102, and 1.0 × 103 M -1, respectively. In chloroform, aggregation of the complex occurs at ~0.3 mM, reflecting the lower solvating power of chloroform for this complex. The 1 H NMR spectra of the chloroform solutions indicate that at concentrations greater than 1.0 mM, two discrete dimers in the ratio of 87:13 are reversibly formed. The 1 H NMR spectra of the major isomer, 2a, suggest that it is the 45 °-staggered cofacial dimer, a dimer with a D4 d symmetry. The 1 H NMR spectra of the minor isomer, 2b, suggest that it is a slipped cofacial dimer with a C2 h symmetry, which is formed by slipping a ( RPc ) Rh plane of the eclipsed dimer (a D4 h dimer) along a line connecting two opposing meso nitrogens of ( RPc ) Rh . Interestingly, the solution conformation of 2b is similar to that of the basic stacking unit found in the crystal structure of 1.

Synthesis and Electrochemistry of Ferrocenylphthalocyanines

A series of phthalocyanines containing 4, 8, and 16 2-ferrocenylethoxy moieties on the periphery have been prepared and spectroscopically characterized. The UV−vis spectrum of the tetraferrocenyl phthalocyanine 4 shows an unusual long-wavelength band at ca. 760 nm in nonpolar solvents. When the spectral changes of this compound and its analogue [1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninato]zinc(II) (12) are studied in different solvents and at various concentrations, along with their fluorescence spectra, it can be concluded that this band is not likely due to a slipped cofacial dimer as reported previously. Compound 4 is not emissive, which can be explained by the efficient quenching due to electron transfer from ferrocene to the excited phthalocyanine. The value of ΔG° for this photoinduced electron transfer has been estimated to be −0.48 eV. Electrochemical studies of these phthalocyanine−ferrocene conjugates by cyclic voltammetry have revealed that all the ferrocenyl redox centers attached to the macrocyclic core are electrochemically independent and undergo an oxidation at the same potential.