Porphyrin light-harvesting arrays constructed in the recombinant tobacco mosaic virus scaffold

We have demonstrated the construction of multiple porphyrin arrays in the tobacco mosaic virus (TMV) supramolecular structures by self-assembly of recombinant TMV coat protein (TMVCP) monomers, in which Zn-coordinated porphyrin (ZnP) and free-base porphyrin (FbP) were site-selectively incorporated. The photophysical properties of porphyrin moieties incorporated in the TMV assemblies were also characterized. TMV-porphyrin conjugates employed as building blocks self-assembled into unique disk and rod structures under the proper conditions as similar to native TMV assemblies. The mixture of a ZnP donor and an FbP acceptor was packed in the TMV assembly and showed energy transfer and light-harvesting activity. The detailed photophysical properties of the arrayed porphyrins in the TMV assemblies were examined by time-resolved fluorescence spectroscopy, and the energy transfer rates were determined to be 3.1-6.4x10(9) s(-1). The results indicate that the porphyrins are placed at the expected positions in the TMV assemblies.     

Fabrication of Microspheres from Phthalimide‐Substituted Porphyrin Derivatives

Microspheres were fabricated from phthalimide‐substituted porphyrin derivatives. Microscopic analysis showed that the structures of the supramolecular assemblies synthesized in the present study were spherical, with diameters in the sub‐micrometer to micrometer range. The size of the microspheres could be controlled by changing the concentration of the casting solution. The spectroscopic properties of the microspheres were measured to determine the influence of their structural components. Thermal studies indicated that the temperature at which these structures became unstable was lower than the bulk melting point. During I–V measurements on devices composed of these microspheres, it was found that the current increased upon light irradiation, and the characteristic photoresponse properties of these devices were reproducible.     

Cycloaddition of Porphyrins to Isatin: Synthesis of Novel Spiro Porphyrin Derivatives

Isatin undergoes regioselective 1,3‐dipolar cycloaddition reactions with porphyrin azomethine ylides derived from Ni(II) β‐formyl‐meso‐tetraphenylporphyrins in the presence of N‐methylglycine to afford novel spiro porphyrin derivatives.     

An Electron‐Deficient Porphyrin Tape

Hexakis(pentafluorophenyl)‐substituted meso–meso‐linked Zn^II–diporphyrin ( 9 ), which was prepared by the acid‐catalyzed cross‐condensation of 1,1,2,2‐tetrapyrroethane ( 5 ) with dipyrromethane dicarbinol ( 6 ), was converted into meso–meso,β‐β,β‐β triply linked Zn^II–diporphyrin 3 by oxidation with 2,3‐dichloro‐5,6‐dicyanobenzoquinone (DDQ) and Sc(OTf)₃. Beside the red‐shifted absorption spectrum and split first oxidation potential that are common to the triply‐linked Zn^II–diporphyrins, diporphyrin 3 exhibited considerably improved chemical stability owing to a lowered HOMO and good solubility in common organic solvents. The two‐photon absorption (TPA) cross‐section and S₁‐state lifetime of compound 3 were 1700 GM and 3.3 ps, respectively.     

Kinetic Control of the Supramolecular Chirality of Porphyrin J‐Aggregates

The aggregation of achiral sulfonatophenyl‐ and phenyl‐meso‐substituted diprotonated porphyrins to chiral J‐aggregates is a hierarchical noncovalent polymerization process preceded by a critical nucleation stage. This allows significant enantiomeric excesses by the formation of a few primary nuclei and the control of their growth by the effect that flows (imperfect mixing) have on the secondary nucleation of the J‐aggregate particles. In addition, the results strongly suggest that when only one species of aggregate predominates, the CD signals of the three excitonic bands in the visible region (around 420, 490, and 700 nm) show the same sign. Thus, differences on their relative sign would be due to the presence of different species.     

Porphyrin

A new previously unknown double intramolecular cyclization has been discovered on thermolyzing nickel complexes of Schiff's bases of porphyrins containing propionic acid ester residues. This leads to the formation of cyclopentaneporphyrin lactams. Using coproporphyrin-I and -II derivatives as examples, the corresponding lactams were obtained, the structures of which were confirmed by PMR spectra using the nuclear Overhauser effect (NOE). A general scheme for the thermal decomposition of Schiff's bases of meso-formylporphyrins is proposed.For Communication 25, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 180–188, February, 1993.     

氢卟啉和镁卟啉分子溶剂效应的理论研究

采用溶剂场极化连续模型在密度泛函B3LYP/6-31G (D)水平上研究了氢卟啉和镁卟啉分子在四氢呋喃(THF)、二甲基亚砜(DMSO)、二氯甲烷(CH2Cl2)、氯仿(CHCl3)这四种不同极性的溶剂环境中的几何结构和分子轨道能级, 从而研究了溶剂效应引起的分子几何构型和轨道能级的变化. 然后采用上述溶剂环境下优化的几何结构在含时密度泛函水平上计算了它们的激发能、吸收波长、跃迁组成和振荡强度. 理论计算结果表明, 对比真空条件下的氢卟啉和镁卟啉分子的几何结构, 溶剂场中两种卟啉分子的几何结构都发生了微弱的变化, 这种变化随溶剂介电常数的增大而有所增强. 计算结果表明溶剂环境中氢卟啉和镁卟啉分子的电子吸收光谱发生了普遍的红移, 结合分子轨道理论对这种变化给出了可能的解释. 在此基础上, 对这种包含溶剂效应的理论分析方法用于检验卟啉类化合物作为染料敏化太阳能电池光敏剂的可行性作了进一步的探讨.     

Effects of Core‐modification on Porphyrin Sensitizers to the Efficiencies of Dye‐sensitized Solar Cells

To study dye‐sensitized solar cells (DSSCs) with core‐modified porphyrins as the sensitizing dyes, three porphyrins with an ethynyl benzoic acid as an anchoring group are prepared. The properties of free‐base regular porphyrin (N4), thiaporphyrin (N3S) and oxaporphyrin (N3O) were thoroughly studied by spectroscopic methods, DFT calculations, and photovoltaic measurements. Replacing one of the porphyrinic core nitrogen atoms by oxygen or sulfur considerably changes the absorption spectra. The Soret band of the N3O and N3S observed bathochromic shifts of 3‐9 nm while the Q band reaches 700 nm to the near‐infrared region. The overall conversion efficiencies of the DSSCs based on these porphyrins are in the order N4 (3.66%) ? N3S (0.22%) > N3O (0.01%). The time‐correlated single photon counting observed short fluorescence lifetimes for N3O adsorbed both on TiO₂ and Al₂O₃ which explicates the poor efficiency of DSSC using N3O as the photosensitizer.     

Unusual Stabilization of Dication Diradical Intermediate of Dizinc(II) Porphyrin Dimer

We have demonstrated here how the nature of a metal ion controls the reactivity of a metalloporphyrin π‐cation radical. One‐electron oxidations of diethylpyrrole‐bridged dicopper(II) and dipalladium(II) porphyrin dimers using iodine as an oxidant result in the formation of strongly interacting cofacial mixed‐valent π‐cation radical dimers. The mixed‐valent cation radical so generated being highly reactive drives a spontaneous and rapid transformation to form an indolizinium‐fused chlorin‐porphyrin heterodimer. In sharp contrast to this, similar addition of iodine leads to 1e‐oxidation of dizinc(II) porphyrin dimer, which is followed by a second oxidation to produce a dication diradical complex. The axial coordination of iodine upon 1e‐oxidation of dizinc(II) porphyrin dimer lowers the overall oxidation potential of the system, and thereby, making the second oxidation easily accessible. This has resulted in the stabilization of a dication diradical complex, in which two porphyrin π‐cation radicals undergo electronic communication through the bridging pyrrole group. Interestingly, despite being well‐separated from each other, the two radical spins undergo strong antiferromagnetic coupling to form a diamagnetic compound. The conjugation also leads to a change in identity of the bridge, which further highlights the critical role played by the bridge in the electronic communication between the two rings. DFT calculations clearly support the experimental observations.     

Synthesis of a Benzenethiol‐derivatized Porphyrin for Self‐assembly

The synthesis of a benzenethiol‐derivatized porphyrin for flat‐lying self‐assembly on gold substrates is described. Acetyl protected thiol is not stable enough in Pd‐catalyzed reactions. While acrylate derivatives protected thiol group shows good tolerance in Pd‐catalyzed borylations and Suzuki‐Miyaura coupling reactions and no catalyst poisoning was observed.     

Porphyrin acids

The structural change from the porphyrin free base to monoacid and diacid by successive protonation has been studied by the IR, visible and NMR spectroscopy. The results have indicated that the cation and anion of the porphyrin diacid are strongly associated through H-bonding. The far IR spectra show especially marked differences in the free base, monoacid, and diacid due to the changes of the inner core of the porphyrin ring.