Photophysical and electrochemical properties of meso-substituted thien-2-yl Zn(II) porphyrins

The influence of the thiophene ring on the ground and excited state properties of the porphyrin ring is investigated, when substituted at the meso-position. A series of mono-, di-, tri-, and tetra- meso-thien-2-yl porphyrins are studied and discussed with respect to the reference compounds zinc(II)-5,10,15,20-tetra(thien-2'-yl)porphyrin ( 1a) and zinc(II)-5,10,15,20-tetraphenylporphyrin (ZnTPP). The extended conjugated system zinc(II)-5-(5'-(5'-ethynyl-2'-thiophenecarboxaldehyde)thien-2'-yl)-10,15,20-triphenylporphyrin ( 4d) is also studied and shows enhanced charge transfer character due to the presence of the terminal aldehyde accepting group. A detailed analysis of ground and excited state UV-vis absorption, steady-state and time-resolved fluorescence, laser flash photolysis, and electrochemical data all point toward substantial electronic communication between the central Zn(II) porphyrin ring and the meso-thien-2-yl substituents, which is evident from excited state charge transfer character.     

Energy transfer in zinc porphyrin-phthalocyanine heterotrimer and heterononamer studied by fluorescence resonance energy transfer (FRET)

Two or eight zinc triphenyl porphyrins were conjugated with Zn-phthalocyanine or H2-phthalocyanine to form ZnPc-(ZnTPP)2, ZnPc-(ZnTPP)8, H2Pc-(ZnTPP)2 and H2Pc-(ZnTPP)8. Energy transfers from the porphyrin moiety to phthalocyanine part were quantitatively studied with the modality of fluorescence resonance energy transfer (FRET). By measuring the fluorescence increment from the phthalocyanine moiety and the decrease from porphyrin part under selective excitation at the B band of the porphyrin part in those conjugated compounds and their equimolar mixture of compositions, energy transfer efficiencies were estimated to be 90% for H2Pc-(ZnTPP)8 and ZnPc-(ZnTPP)8, and 60%, 30% for ZnPc-(ZnTPP)2 and H2Pc-(ZnTPP)2, respectively.     

A directly fused tetrameric porphyrin sheet and its anomalous electronic properties that arise from the planar cyclooctatetraene core

Oxidation of a directly meso-meso linked cyclic porphyrin tetramer 2 gave a porphyrin sheet 3. The symmetric square structure of 3 is indicated by its simple 1H NMR spectrum that exhibits only two signals for the porphyrin beta-protons. The absorption spectrum of 3 displays characteristic Soret-like broad bands and weak Q-bands, and its magnetic circular dichroism (MCD) spectrum exhibits a negative Faraday A term at the 762 nm band as a rare case, indicating the absorption as a transition from a nondegenerate level to a degenerate level. A slightly longer S1-state (1.1 ps) and smaller TPA cross section (2750 GM) than a tetrameric linear porphyrin tape also indicate its unique electronic properties. The porphyrin sheet 3 forms stable 1:2 complexes with guest molecules G1 and G2, whose 1H NMR spectra exhibit remarkable downfield shifts for the guest protons that are located just above the cyclooctatetraene (COT) core of 3, whereas the imidazolyl protons bound to the zinc(II) porphyrin local cores are observed at slightly upfield positions. These results have been qualitatively accounted for in terms of the presence of a strong paratropic ring current around the COT core that propagates through the whole pi-electronic network of 3, hence competing with and cancelling the weak diatropic ring currents of the local zinc(II) porphyrins. This explanation was supported by DFT calculation performed at the GIAO-B3LYP/6-31G level, which indicated large positive NICS values within the COT core and small NICS values within the local zinc(II) porphyrins.     

Theoretical investigation of one-photon and two-photon absorption properties for multiply N-confused porphyrins

We have theoretically investigated a series of multiply N-confused porphyrins and their Zn or Cu complexes for the first time by using DFT(B3LYP/6-31G*) and ZINDO/SOS methods. The electronic structure, one-photon absorption (OPA), and two-photon absorption (TPA) properties have been studied in detail. The calculated results indicate that the OPA spectra of multiply N-confused porphyrins are red-shifted and the OPA intensities decrease compared to normal porphyrin. The maximum two photon absorption wavelengths lambda(max) are blue-shifted and the TPA cross sections delta(max) are increased 22.7-112.1 GM when the N atoms one by one are inverted from core to beta position to form multiply N-confused porphyrins. Especially delta(max) of N3CP get to 164.7 GM. The electron donors -C6F5s at meso-position can make the TPA cross section delta(max) increase. After forming metal complexes with Cu or Zn, the TPA properties of multiply N-confused porphyrins are further increased except for N3CP, N4CP. Our theoretical findings demonstrate that the multiply N-confused prophyrins as well as their metal complexes and derivatives are promising molecules that can be assembled series of materials with large TPA cross section, and are sure to be the subject of further investigation.     

Zinc(II) porphyrins at the air-water interface as studied by polarized total-reflection X-ray absorption fine structure

The polarized total-reflection X-ray absorption fine structure method was applied to characterize zinc porphyrins at the air-water interface. The X-ray absorption near edge structure exhibited a significant difference depending on the polarization of the X-ray. A shoulder peak of the Zn K-edge corresponding to the 1s-4p(z) transition for a square planar metal complex without axial coordination(s) was observed at 9662 eV, which indicates that the axial coordination sites of zinc porphyrin molecules examined are not fully hydrated at the air-water interface. The molecular orientation of zinc porphyrins was determined by analyzing the polarization dependence of the transition peak intensity. The meso-substituted porphyrin derivative 5,10,15,20-tetraphenylporphyrinatozinc(II) (ZnTPP) orients rather parallel to the solution surface. In contrast to ZnTPP, the zinc(II) protoporphyrin IX (ZnPP) with hydrophilic carboxyl groups at one side of the molecule stands up with respect to the solution surface, and the average tilting angle of the porphyrin plane to the surface was evaluated to be between 57 degrees and 43 degrees. In addition, the axial coordination of ZnPP is modified depending on the surface concentration, in which the axial hydration to the zinc center is effectively inhibited in the compressed surface layer.     

Flexible Tuning of Unsaturated β‐Substituents on Zn Porphyrins: A Synthetic,Spectroscopic and Computational Study

A series of zinc porphyrins substituted at adjacent β‐positions with a CN group and para‐substituted ethenyl/ethynyl‐phenyl group have been studied using electronic absorption spectroscopy, resonance Raman spectroscopy and DFT calculations. The oxidative nucleophilic substitution of hydrogen was utilized for the introduction of a cyano substituent on the porphyrin ring. This modification has a remarkable electronic effect on the ring. The resulting porphyrin cyanoaldehyde was further modified in Wittig condensations to give series of arylalkene‐ and arylalkyne‐substituted derivatives. This substitution pattern caused significant redshifting and broadening of the B band, tuning from 433–446 nm. Additionally the Q/B band intensity ratios show much higher values than observed for the parent porphyrin ZnTPP (0.20 vs. 0.03). Careful analysis of the electronic transitions using DFT and resonance Raman spectroscopy reveal that the substituent does not significantly perturb the electronic structure of the porphyrin core, which is still well described by Gouterman’s four‐orbital model. However, the substituents do play a role in elongating the conjugation length and this results in the observed spectral changes.     

An insight into a novel class of self-assembled porphyrins: geometric structure, electronic structure, one- and two-photon absorption properties

We have theoretically investigated a series of butadiyne-linked porphyrin derivatives that exhibit large two-photon absorption (TPA) cross sections in the visible-IR range. The electronic structure, one-photon absorption (OPA), and TPA properties have been studied in detail. We found that the introduction of a butadiyne linkage and the increase of the molecular dimensionality from monomer to dimer determine the OPA intensities of Q band and Soret band, respectively. A most important role for the enhancement of the TPA cross section is played by introducing a butadiyne bridge. The complementary coordination and the combination of the terminal free base and the core zinc porphyrin are also two effective factors for the enhancement of the TPA efficiency. The dimer with two porphyrins linked at meso-positions by a butadiyne linkage results in a maximum TPA cross section (79.35 x 10(-48) cm4 s per photon). Our theoretical findings are consistent with the recent experimental observations. This series of porphyrin derivatives as promising TPA materials are the subject of further investigation.     

Synthesis, Characterization and Weak Intramolecular Interactions of Porphyrins Bearing Nucleobases

5,10, 15-Triphenyl-20-{2- [α- (adenine-9 ) acetylamino]} phenyl porphyrin ( 1 ), 5,10, 15-triphenyl-20-{2-[α-(cytosine-1)acetylamino]} phenyl porphyrin (2), 5, 10, 15-triphenyl-20-{4-[α-(cytosine-1)ethoxy]} phenyl porphyrin (3) and their zinc complexes Zn-1, Zn-2 and Zn-3 have been prepared and characterized by ^1H NMR spectra, elemental analyses, electronic absorption spectra and mass spectra (FAB). Intramolecular π-π interactions and intramolecular metal-~ interaction for 1, 2, Zn-1,and Zn-2 have been investigated by several methods. ^1H NMR studies demonstrate that the porphyrin π-system in 1 and 2 is parallel to the adenine and the cytosine aromatic ring, respectively. The electronic absorption spectral properties of free porphyrin derivatives and their zinc complexes have been compared with those of H2TPP and ZnTPP. The results show that the UV-vis spectra of 1 and 2 are the same as that of H2TPP,whereas the spectra of their zinc complexes show 7 nm red shifts of the Soret bands compared to that of ZnTPP. The emission spectra of Zn-1 and Zn-2 are independent of excitation wavelength. From combination of the evidence of absorption and emission spectra it is suggested the existence of intramolecular metal-π interaction in Zn-1 and Zn-2. The results of conformational analysis agreed quite nicely with that of experiments, thus it was further to validate the experimental conclusions.     

Swallowtail porphyrins: synthesis, characterization and incorporation into porphyrin dyads

The incorporation of symmetrically branched tridecyl ("swallowtail") substituents at the meso positions of porphyrins results in highly soluble building blocks. Synthetic routes have been investigated to obtain porphyrin building blocks bearing 1-4 swallowtail groups. Porphyrin dyads have been synthesized in which the zinc or free base (Fb) porphyrins are joined by a 4,4'-diphenylethyne linker and bear swallowtail (or n-pentyl) groups at the nonlinking meso positions. The swallowtail-substituted Zn(2)- and ZnFb-dyads are readily soluble in common organic solvents. Static absorption and fluorescence spectra and electrochemical data show that the presence of the swallowtail groups slightly raises the energy level of the filled a(2u)(pi) HOMO. EPR studies of the pi-cation radicals of the swallowtail porphyrins indicate that the torsional angle between the proton on the alkyl carbon and p-orbital on the meso carbon of the porphyrin is different from that of a porphyrin bearing linear pentyl groups. Regardless, the swallowtail substituents do not significantly affect the photophysical properties of the porphyrins or the electronic interactions between the porphyrins in the dyads. In particular, time-resolved spectroscopic studies indicate that facile excited-state energy transfer occurs in the ZnFb dyad, and EPR studies of the monocation radical of the Zn(2)-dyad show that interporphyrin ground-state hole transfer is rapid.     

Very large infrared two-photon absorption cross section of asymmetric zinc porphyrin aggregates: Role of intermolecular interaction and donor-acceptor strengths

Very large two-photon absorption (TPA) cross sections at the infrared region have been revealed for J-aggregates of asymmetric zinc porphyrin using quantum-chemical calculation. The TPA properties are evaluated for monomer and aggregates of a series of push-pull porphyrins, whose syntheses are known in the literature. The two-photon absorption cross section can be greatly enhanced by increasing the strengths of the electron donor/acceptor. We also present a quantum-chemical analysis on porphyrin aggregates to understand the role of intermolecular interactions and the relationship between structural and collective nonlinear optical properties. It has been observed that the TPA properties change tremendously as monomers undergo J-aggregation and the magnitudes of TPA cross sections are highly dependent on the nature of aggregates. The importance of our results with respect to the design of photonic and photodynamic therapy materials has been discussed.     

Light-harvesting energy transfer and subsequent electron transfer of cationic porphyrin complexes on clay surfaces

A novel energy-transfer system involving nonaggregated cationic porphyrins adsorbed on an anionic-type clay surface and the electron-transfer reaction that occurs after light harvesting are described. In the clay-porphyrin complexes, photochemical energy transfer from excited singlet zinc porphyrins to free-base porphyrins proceeds. The photochemical electron-transfer reaction from an electron donor in solution (hydroquinone) to the adsorbed porphyrin in the excited singlet state was also examined. Because the electron-transfer rate from the hydroquinone to the excited singlet free-base porphyrin is larger than that to the excited singlet zinc porphyrin, we conclude that the energy transfer accelerates the overall electron-transfer reaction.     

手性Boc保护氨基酸修饰卟啉的合成及谱学研究

合成了α,α,α,β-四-[邻(叔丁氧羰丙氨酸)氨基苯基]卟啉H₂T(o-BocAla)APP(1)及其锌()配合物ZnT(o-BocAla)APP(Zn^-1),α,α,α,β-四-[邻(叔丁氧羰苏氨酸)氨基苯基]卟啉H₂T(o-BocThr)APP(2)及其锌(Ⅱ)配合物ZnT(o-BocThr)APP(Zn-2),α,α,α,β-四-[邻(叔丁氧羰酪氨酸)氨基苯基]卟啉H₂T(o-BocTyr)APP(3)及其锌()配合物ZnT(o-BocTyr)APP(Zn-3)等6种叔丁氧羰保护氨基酸修饰的卟啉.用元素分析、核磁共振、红外光谱、紫外-可见光谱以及圆二色谱等手段对其组成的结构进行了表征,并对其谱学性质进行了研究.     

Synthesis,Spectral, and Coordination Properties of Halogen-Substituted Tetraarylporphyrins

2,3,7,8,12,13,17,18-Ocatbromo-5,10,15,20-tetra-(4-chloroprienyl)porphyrin and 2,3,7,8,12,13,17,18-octachloro-5,10,15,20-tetra-(4-bromophenyl)porphyrin have been synthesized. The obtained compounds have been identified by electronic absorption and ¹H NMR spectroscopy as well as mass spectrometry. The complex-forming properties of the synthesized porphyrins in the zinc acetate (II)-acetonitrile system at 278–298 K have been studied. Kinetic parameters of the formation of the corresponding zinc complexes in acetonitrile have been determined.

     

New synthesis of zinc tetrakis(arylethynyl)porphyrins and substituent effects on their redox chemistry

Sonogashira coupling of zinc 5,10,15,20-tetraethynylporphyrin with various phenyl iodides under mild conditions afforded good yields of the corresponding zinc porphyrins. This method is applicable to a variety of aryl iodides including meso-substituted iodoporphyrin to form a conjugated star-shaped multiporphyrin. The UV-Vis spectra show that peak broadening, red shifts, and changes in the oscillator strength of absorptions increase with the extension of pi-conjugation. In the electrochemical measurements, the first oxidation of porphyrins 4-9 occurs at potentials in the range +0.89 to +1.08 V, which are comparable to that of ZnTPP (TPP = tetraphenylporphyrin). The first reduction was observed at potentials from -0.73 to -0.89 V, which is anodically shifted by 390-550 mV as compared to that of ZnTPP, and the second reduction occurs at potentials in the range -1.12 to -1.33 V. The para-substituted tetrakis(phenylethynyl)porphyrins show substituent effects on their redox chemistry and exhibit only slight substituent effects in their emission and absorption maxima.     

Coronenetetraimide‐Centered Cruciform Pentamers Containing Multiporphyrin Units: Synthesis and Sequential Photoinduced Energy‐ and Electron‐Transfer Dynamics

A series of coronenetetraimide (CorTIm)‐centered cruciform pentamers containing multiporphyrin units, in which four porphyrin units are covalently linked to a CorTIm core through benzyl linkages, were designed and synthesized to investigate their structural, spectroscopic, and electrochemical properties as well as photoinduced electron‐ and energy‐transfer dynamics. These systems afforded the first synthetic case of coroneneimide derivatives covalently linked with dye molecules. The steady‐state absorption and electrochemical results indicate that a CorTIm and four porphyrin units were successfully characterized by the corresponding reference monomers. In contrast, the steady‐state fluorescence measurements demonstrated that strong fluorescence quenching relative to the corresponding monomer units was observed in these pentamers. Nanosecond laser flash photolysis measurements revealed the occurrence of intermolecular electron transfer from triplet excited state of zinc porphyrins to CorTIm. Femtosecond laser‐induced transient absorption measurements for excitation of the CorTIm unit clearly demonstrate the sequential photoinduced energy and electron transfer between CorTIm and porphyrins, that is, occurrence of the initial energy transfer from CorTIm (energy donor) to porphyrins (energy acceptor) and subsequent electron transfer from porphyrins (electron donor) to CorTIm (electron acceptor) in these pentamers, whereas only the electron‐transfer process from porphyrins to CorTIm was observed when we mainly excite porphyrin units. Finally, construction of high‐order supramolecular patterning of these pentamers was performed by utilizing self‐assembly and physical dewetting during the evaporation of solvent.     

Mechanisms, pathways, and dynamics of excited-state energy flow in self-assembled wheel-and-spoke light-harvesting architectures

Static and time-resolved optical measurements are reported for two cyclic hexameric porphyrin arrays and their self-assembled complexes with guest chromophores. The hexameric hosts contain zinc porphyrins and 0 or 3 free base (Fb) porphyrins (denoted Zn(6) or Zn(3)Fb(3), respectively). The guests are a tripyridyl arene (TP) and a dipyridyl-substituted free base porphyrin (DPFb), each of which coordinates to zinc porphyrins of a host via pyridyl-zinc dative bonding. Each architecture is designed to have an overall gradient of excited-state energies that affords excitation funneling within the host and ultimately to the guest. Collectively, the studies delineate the various pathways, mechanisms, and rate constants of energy flow among the weakly coupled constituents of the host-guest complexes. The pathways include downhill unidirectional energy transfer between adjacent chromophores, bidirectional energy migration between identical chromophores, and energy transfer between nonadjacent chromophores. The energy transfer to the lowest-energy chromophore(s) within the backbone of a hexameric host (Fb porphyrins in Zn(3)Fb(3) or pyridyl-coordinated zinc porphyrins in Zn(6)*TP and Zn(6)*DPFb) proceeds primarily via a through-bond mechanism; the transfer is rapid (approximately 40 ps depending on the array) and essentially quantitative (>or=98%). The energy transfer from a pyridyl-coordinated zinc porphyrin of the host to the Fb porphyrin guest in the Zn(6)*DPFb complex is almost exclusively F?rster through-space in nature; this process is much slower ( approximately 1 ns) and has a lower yield (65%). These studies highlight the utility of cyclic architectures for efficient light harvesting and energy transfer to a designated trapping site.     

ms-四咪唑基卟啉络合金属离子的能力及其金属络合物的催化性能

本文考察了两种ms-四咪唑基卟啉〔H₂T(2-I)P和H₂T(4或5-I)P〕对锌离子的络合能力,并与ms-四苯基卟啉〔H₂TPP〕进行了比较。用ms-四咪唑基金属卟啉〔MT(2-I)P和MT(4或5-I)P〕作为催化剂,以分子氧为氧源,考察了对氢醌、异丙硫醇和抗环血酸三种底物氧化反应的催化活性。在后一底物的氧化反应中对CoT(2-I)P,CoT(4或5-I)P和CoTPP进行了对比。此外,还用EHMO程序计算了卟吩、ms-四咪唑基卟啉、ms-四苯基卟啉及其锌络合物的净电荷分布和能量,对反应结果作了比较满意的解释。     

Investigation on DNA Binding and Photo-Cleavage Properties of Water-Soluble Porphyrin and Metalloporphyrins

A water-soluble porphyrin, tetrakis[4-(trimethylammonium)phenyl]porphyrin (TAPP), and its metal complexes with Zn(II), (ZnTAPP), have been synthesized and characterized by elemental analyses and u.v.-vis. spectra. The binding of the two complexes with calf thymus DNA has been investigated by absorption spectra, luminescence titrations, and viscosity measurements. The changes of the u.v.-vis. absorption spectra during the titration of these porphyrins with calf thymus DNA revealed a large bathochromic shift (upto 8–12 nm) and a hypochromicity of the porphyrins soret bands. The intensity of the fluorescence spectra of these porphyrins was enhanced. The cytotoxicity of the series of porphyrins TAPP and MTAPP [M = Zn(II), Cu(II), Fe(III), Co(III), Ni(II), Mn(III)] complexes was determined for Madin–Darby Canine Kindney (MDCK) cells and Vero cells with the method of cell culture, and were evaluated as anti-virus activity for influenza virus type A (H3N2), B and Herpes simplex virus type-1 (HSV-1, strain SM44), type-2 (HSV-2, strain 333) in vitro. Among the complexes evaluated, inhibited viral cytopathogenicity at lower concentrations that were found cytotoxic for the MDCK cells. Differences were observed in the 50% effective doses (based on inhibition of viral cytopathogenicity) of these complexes for a number of influenza viruses type A, B, and HSV-1, HSV-2 strains. It was found that CoTAPP displayed good inhibitory action against the virus in vitro.     

Photophysics of untethered ZnTPP-fullerene complexes in solution

The spectroscopy and dynamic behavior of the self-assembled, Soret-excited zinc tetraphenylporphyrin (ZnTPP) plus fullerene (C(60)) model system in solution has been examined using steady state fluorescence quenching, nanosecond time-correlated single photon counting, picosecond fluorescence upconversion, and picosecond transient absorption methods. Evidence of ground state complexation is presented. Steady-state quenching of the S(2) and S(1) fluorescence of ZnTPP by C(60) reveals that the quenching processes only occur in the excited complexes, are ultrafast, and proceed at different rates in the two states. Only uncomplexed ZnTPP is observed by fluorescence lifetime methods; the locally excited complexes are either dark or, more likely, rapidly relax to products that do not radiate strongly. Both short-range (Dexter) energy transfer and electron transfer relaxation mechanisms are evaluated. Picosecond transient absorption data obtained from the subtle differences between the spectra of Soret-excited ZnTPP with and without a large excess of added C(60) reveal the formation, on a subpicosecond time scale, of relatively long-lived charge-separated species. Soret excitation of ZnTPP···C(60) does not produce a quantitative yield of species in the lower S(1) excited state.     

Dynamics of closure of zinc bis-porphyrin molecular tweezers with copper(II) ions and electron transfer

Zinc bis-porphyrin molecular tweezers composed of a N(4) spacer bound through pyridyl units to the meso position of porphyrins were synthesized, and the tweezers are closed by the coordination of a copper(II) ion inside the spacer ligand. The effect of the π-π interaction between the porphyrin rings in the closed conformation on the absorption spectra of multi-electron oxidized species and the reduction potentials were clarified by chemical and electrochemical oxidation of the closed form of the zinc bis-porphyrin molecular tweezers in comparison with the open form without copper(II) ion and the corresponding porphyrin monomer. The shifts in redox potentials and absorption spectrum of the porphyrin dication indicate a strong electronic interaction between the two oxidized porphyrins in the closed form, whereas there is little interaction between them in the neutral form. The dynamics of copper(II) ion coordination and subsequent electron transfer was examined by using a stopped-flow UV/Vis spectroscopic technique. It was confirmed that coordination of copper(II) occurs prior to electron-transfer oxidation of the closed form of the zinc bis-porphyrin molecular tweezers.