Zinc Meso-tetraphenylporphyrin Research Articles

Self-assembled supramolecular triad composed of fulleropyrrolidine bearing two pyridine moieties axially coordinated to two zinc porphyrins

Spectroscopic, redox, and photochemical behavior of a self-assembled donor-acceptor triad formed by axial coordination of zinc meso-tetraphenylporphyrin, Zn ( TPP ) with fulleropyrrolidine bearing two pyridine moieties ( C 60( Py )2) was investigated. The UV-visible and 1 H NMR spectral studies revealed supramolecular 1:2 triad formation between C 60( Py )2 and Zn ( TPP ). The determined overall formation constant, K was as large as 1.45 × 104 mol -2 in o-dichlorobenzene (o-DCB). The 1 H NMR studies revealed axial coordination of both the pyridine entities of C 60( Py )2 to the central metal ion of the zinc porphyrins. Electrochemical studies of the isolated self-assembled triad in o-DCB established the molecular stoichiometry of the supramolecular complex possessing one C 60( Py )2 and two Zn ( TPP ) entities. The excited state electron transfer reactions were monitored by both steady-state emission as well as transient absorption techniques. In o-DCB, upon coordination of the pyridine entities of C 60( Py )2 to two Zn ( TPP ), the main quenching pathway involved charge-separation from the singlet excited Zn ( TPP ) to the C 60 moiety. However, in a coordinating solvent like PhCN , intermolecular electron-transfer takes place from the triplet excited state of Zn ( TPP ) to the C 60 moiety.

Analysis of Absorption Spectra of Zinc Porphyrin, Zinc meso-Tetraphenylporphyrin, and Halogenated Derivatives

The absorption spectra of zinc porphyrin, zinc meso-tetraphenylporphyrin, and their β-halogenated derivatives are calculated and analyzed using time-dependent density functional theory (TDDFT) and time-dependent Hartree−Fock theory based on the intermediate neglect differential overlap/spectroscopic approximation (TDHF-INDO/S) to obtain the origin of the spectral shifts in color and intensity. Analysis of the spectral shifts is carried out to account for the effects of phenyl, fluoro, chloro, and bromo substituents on the spectra. The spectroscopic trends predicted by TDHF-INDO/S compare well with the more accurate time-dependent density functional theory results and with available experimental data.

Ground and Triplet Excited Structures and Spectroscopic Properties of Halogenated Zinc meso-Tetraphenylporphyrin

Structures of the ground and triplet excited state of zinc meso-tetraphenylporphyrin (ZnTPP) and its β-octahalogenated derivatives (ZnTPPX8 with X = F, Cl, and Br) have been predicted using density functional theory (DFT) with Becke's three-parameter functional. The excitation energies, computed by singles CI and time-dependent DFT (TDDFT), are consistent with the observed trends, with TDDFT values in near quantitative agreement with experiment. For ZnTPPBr8, we found that geometry distortion contributes about one-third of the redshifts observed for the Q and B bands in the ground-state spectrum. The results for ZnTPPX8 and the nonphenylated ZnPX8 provide insightful accounts of effects of phenyl, fluoro, chloro, and bromo substituents on the excitation energies of these systems. The computed singlet−triplet (S0−T1) splitting of ZnTPP is in excellent agreement with experiment. The S0−T1 splitting is predicted to be significantly (0.4−0.5 eV) redshifted upon β-chlorination and β-bromination.

A new pyridyl-substituted methanofullerene derivative. Photophysics, electrochemistry and self-assembly with zinc(II) meso-tetraphenylporphyrin (ZnTPP)

A new methanofullerene derivative with a pyridine residue at the methano bridge (PC60) has been synthesized. Its electrochemical and photophysical properties have been investigated in toluene solution along with those of the analogous fullerene mono-malonate adduct RC60, which does not contain the pyridyl moiety. PC60 and RC60 display almost identical steady state absorption and luminescence properties and transient absorption spectra, as shown by means of nano- and picosecond laser flash photolysis. Their markedly different spectroscopic features with respect to plain C60 are discussed, with the aid of semi-empirical calculations. PC60 binds zinc(II) meso-tetraphenylporphyrin (ZnTPP) through coordination of the pyridyl moiety to the zinc ion giving, to the best of our knowledge, the first non-covalent assembly of a porphyrin–fullerene diad. The association constant of the 1:1 complex between PC60 and ZnTPP has been determined at 300 K by 1H NMR (Ka=3600±150 L mol-1, C6D6 solution) and fluorescence titrations (Ka=3000±400 L mol-1, toluene solution). Mixtures of RC60 and ZnTPP have also been investigated, giving no evidence of association. Extremely fast ZnTPP luminescence quenching in the PC60–ZnTPP complex was observed by time-resolved luminescence spectroscopy (k>5×1010 s-1), tentatively attributed to an energy transfer mechanism. The bimolecular quenching constant of the lowest triplet excited state of ZnTPP by PC60 was determined via a Stern–Volmer analysis (kq=6.7×109 s-1).

Ultrafast relaxation times of metalloporphyrins by time-resolved degenerate four-wave mixing with incoherent light

We present experimental results on the measurement of the population-relaxation times of the excited states of some metalloporphyrins such as zinc meso-tetra-phenylporphyrin (ZnmTPP), zinc meso-tetra (p-methoxyphenyl) tetrabenzporphyrin (ZnmpTBP), tetratollylporphyrin (TTP), cobalt tetratollylporphyrin (CoTTP) and nickel tetratollylporphyrin (NiTTP) with time-resolved degenerate four-wave mixing with the incoherent emission of a nanosecond pumped-dye laser. The experiments are carried out in the counterpropagating geometry (k4=k1+k2-k3), where k1 and k2 are counterpropagating to one another and k3 is at angle θ (<90° with respect to k1). Excited-state and ground-state relaxation times are calculated based on the theoretical formalism developed by Hiromi Okamoto [J. Opt. Soc. Am. B, 10, 2353, 1993]. The signals are recorded by delaying the probe beam (k3) for different fixed delays of the backward pump beam (k2). We observe strong signal at a second peak owing to the coherence of beams k2 and k3 for samples exhibiting excited-state absorption and a narrow peak corresponding to the coherence of beams k1 and k3 for samples that do not exhibit excited-state or reverse-saturable absorption. The nonlinear absorption is studied with the Z-scan technique. From the experimental data, we estimate the relaxation times of excited states.

Molecular Motions of .beta.-Carotene and a Carotenoporphyrin Dyad in Solution: A Carbon-13 NMR Spin-Lattice Relaxation Time Study

Analysis of [sup 13]C NMR spin-lattice relaxation times (T[sub 1]) yields information concerning both overall tumbling of molecules in solution and internal rotations about single bonds. Relaxation time and nuclear Overhauser effect data have been obtained for [Beta]-carotene and two related molecules, squalane and squalene, for zinc meso-tetraphenylporphyrin, and for a dyad consisting of a porphyrin covalently linked to a carotenoid polyene through a trimethylene bridge. Squalane and squalene, which lack conjugated double bonds, behave essentially as limp string, with internal rotations at least as rapid as overall isotropic tumbling motions. In contrast, [Beta]-carotene reorients as a rigid rod, with internal motions which are too slow to affect relaxation times. Modeling it as an anisotropic rotor yields a rotational diffusion coefficient for motion about the major axis which is 14 times larger than that for rotation about axes perpendicular to that axis. The porphyrin reorients more nearly isotropically and features internal librational motions about the single bonds to the phenyl groups. The relaxation time data for the carotenoporphyrin are consistent with internal motions similar to those of a medieval military flail. 31 refs., 3 figs., 5 tabs.

Zinc meso-tetraphenylporphyrin as shift reagent for NADH-models

By the use of zinc meso-tetraphenylporphyrin as a shift reagent the conformations of two new NADH-models have been determined. Induced 1H-NMR shifts up to five ppm have been observed. The conformations determined in this study are consistent with theoretical calculations and NOE-measurements. It has been proven that zinc, which is a co-catalyst in the reduction of activated carbonyl compounds with NADH-models, coordinates to the oxygen of the amide groups in two of our model compounds.

ENDOR studies of π-electron delocalization in covalently linked porphyrin dimers. Model systems for the primary donor in photosynthesis?

The spin density distributions in the cation radicals of various covalently linked tetraphenyl porphyrin dimers and of their monomeric constituents have been studied by liquid-phase EPR, ENDOR and TRIPLE resonance methods to find out whether the dimer systems show intramolecular electron delocalization. Such delocalization is known to occur in the bacteriochlorophyll dimer (‘special pair’) in photosynthetic reaction centres. The dimers studied in this work are derived from zinc meso-tetraphenylporphyrin (ZnTPP) moieties linked either by a phenyl ring at para and meta positions or by a —CH2— bridge at para positions. 1H and 14N hyperfine coupling constants were measured for the dimer and ZnTPP cation radicals. By comparing the hyperfine data it was concluded that in the phenyl-bridged porphyrin dimers the unpaired electron is delocalized over the dimer halves (similar to the ‘special pair’) whereas in the CH2-bridged dimer the unpaired electron is localized on one porphyrin unit.

Photoreduction of alkyl viologens by zinc tetraphenylporphyrin in organic solvent-water systems

Light-induced redox reactions between zinc meso-tetraphenylporphyrin (ZnTPP) and alkyl viologens (C n V 2+) in organic solvent-surfactant-water solutions have been investigated as functions of (i) organic solvent content of solutions, (ii) surfactant charge, and (iii) alkyl viologen hydrophobicity. The best system appears to be an oil-in-water emulsion containing 5 × 10 −5 M ZnTPP and 10 −3 M C 10V 2+ stabilized by cationic surfactants (hexadecyltri-methylammonium bromide or chloride) with 6% N, N'-dimethylformamide (DMF), N, N'-dimethylacetamide (DMAC) or dimethyl sulfoxide (DMSO) in water.

Kinetics of complex formation between zinc meso-tetraphenylporphyrin and some nitrogen bases in aprotic solvents, studied by an improved microwave temperature-jump method

Download options Please wait... Article information DOI https://doi.org/10.1039/F19827801923 Article type Paper Download Citation J. Chem. Soc., Faraday Trans. 1, 1982,78, 1923-1935 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Kinetics of complex formation between zinc meso-tetraphenylporphyrin and some nitrogen bases in aprotic solvents, studied by an improved microwave temperature-jump method E. F. Caldin and J. P. Field, J. Chem. Soc., Faraday Trans. 1, 1982, 78, 1923 DOI: 10.1039/F19827801923 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Edward F. Caldin John P. Field

15N nuclear magnetic resonance studies of ligand binding to zinc tetraphenylprophyrin

Porphyrin 15N chemical shifts of complexes formed by zinc meso-tetraphenylporphyrin and substituted pyridines may be correlated with the electron donating ability of the pyridine substituent.