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Seeding and autocatalytic reduction of platinum salts in aqueous surfactant solution using ascorbic acid as the reductant leads to dendritic metal nanostructures. Synthetic control over the morphology of these Nan dendrites, nanosheets and nanostructured foams is realized by using a tin-porphyrin photocatalyst to conveniently and effectively produce a large initial population of catalytic growth centers.

The view that the large red shifts seen in the UV-visible adsorption bands of peripherally crowded nonplanar porphyrins are the result of nonplanar deformations of the macrocycle is challenged by the suggestion that the red shifts arise from substituent-induced changes in the macrocycle bond length and bond angles. Results of studies suggest that UV-visible band shifts of tetrapyrroles in proteins are potentially useful indicators of changes in nonplanarity provided other structural and electronic factors can be eliminated.

Research has been conducted on nickel(II) porphyrins. The electrochemistry of these compounds has been investigated in the effort to understand the effect of structural and electronic factors on electron-transfer processes in porphyrins, and the details are reported.

Research has been conducted on the reaction of porphyrins with osmium tetraoxide. The effect of the electron-donating and electron-withdrawing substituents on these porphyrins has been investigated.

A study was conducted to examine the effects of the symmetry of substitution pattern and substituent orientations on the out-plane and in-plane distortions of the macrocyle of nickel porphyrins. These nickel porphyrins were analyzed through the use of molecular mechanics calculations, X-ray crystallography, UV visible absorption spectroscopy and resonance Raman spectroscopy. Results revealed that out-plane and in-plane distortions were dependent on perturbation symmetry of the peripheral substituents.

Research was conducted to study the influence of central metals of various sizes on the macrocyclic structure of a series of 5,15-disubstituted metallophorphyrins. Methodologies used included X-ray crystallography, resonance Raman spectroscopy and molecular mechanics. The contributions of the ruf and dom deformations in the crystal structures of several metal complexes of the phorphyrins were found to be metal-dependent. Results indicate the quantitative validity of normal-coordinate structural decomposition.

X-ray crystallography and proton nuclear magnetic resonance spectroscopy were done to determine the structure of symmetrically and asymmetrically highly substituted porphyrins. The results showed that the decasubstituted free-base porphyrins with two meso-aryl substituents have a negligible out-of-plane distortion but a large amount of in-plane distortion, with the corresponding nickel(II) complexes having either planar or modestly nonplanar arrangements. The nickel(II) complexes of 5,15-diethyl-substituted porphyrins, on the other hand, were found to have very ruffled conformations, in spite of the planar arrangement of the corresponding free-base porphyrins.

The regioselective oxidation of pyrrole units in porphyrin and chlorin systems by OsO4 were analyzed to determine the kinetic properties of the synthetic process. Analysis of the OsO4-mediated regioselective oxidation of porphyrin and chlorin systems indicated the role of electron-withdrawing groups at various points of the macrocycles in modulating the synthetic reaction. Furthermore, the position and number of electron-withdrawing groups at various points of the substituents also affected their migratory behavior during pinacol-pinacolone rearrangements.

The effect of substituents with increasing steric demands on the structure of nickel(II) 5,15-disubstituted porphyrins was studied by X-ray crystallography, UV-visible absorption spectroscopy, resonance Raman spectroscopy, molecular energy optimization computations and INDO/s molecular orbital computations. Findings showed that the distortion of the macrocyle for the disubstituted nickel porphyrins is a combination of ruffling and doming distortions. Also, the gal distortion can be precisely described in terms of displacements along the lowest-frequency normal coordinates of B1u and A2u symmetry.

Proton NMR spectroscopic and molecular mechanic studies of seven dodecasubstituted porphyrins reveal that these compounds possess identical structures in both solution and solid states, implying the presence of cavities in solution also. The compounds with these cavities react with 1,3,5-trinitrobenzene to result in pi-complexes and find application as oxidation catalysts with good optical selectivity. The presence of the cavities modifies the physical and chemical properties of the porphyrins.

X-ray studies help determine the crystal structures of Cu(II) octaethyltetraphenyl porphyrin (OTEPP) and its pi cation radical. Oxidation of Cu(II)OETPP stimulates further deformations of the porphyrin skeleton and the product radical exhibits more distortion than the parent compound. Optical and IR spectral data of cation species are similar to that of the Pi cation radical. NMR spectrum reveals the species as diamagnetic. Spectral data reveal the antiferromagnetic coupling between Cu(II) and the nonplanar pi radical spins in the cation radical.

MCD spectroscopic studies of the electronic structures and coordination behaviors of three nickel porphyrins that have different patterns and amounts of macrocycle deformations reveals A-term peaks for all three compounds, indicating that both ruffled and saddle-shaped conformations retain D(2d) symmetry. MCD spectra of Ni(II) protoporphyrin IX-reconstituted hemoglobin ((Ni)Hb) and myoglobin ((Ni)Mb) reveal that protein does not influence the energy level of nickel porphyrins.

X-ray studies of 3,5,7,13,15,17-hexaethyl-2,8,12,18-tetramethylporphyrin (H2DAP) crystals reveal an elongated planar macrocycle along the 5,15 axis that cancels the steric interference of the meso and pyrrole ethyl groups. Another decaalkylporphyrin NiDAP, reveals nonplanar distortion in the porphyrin unit to relieve steric crowding. Optical spectroscopy, NMR and MO calculations help examine solution conformations of H2DAP and NiDAP. Low-temperature NMR studies reveal cis and trans conformation of the methyl groups of the meso ethyls in H2DAP and ZnDAP.

Time-resolved and steady-state optical analyses of a series of planar and nonplanar metal-free porphyrins reveal the influence of structural perturbations on the electronic characteristics of the porphyrin system. Optical data reveal the mechanisms of excited-state dynamics and major decay routes induced by structural parameters. Nonplanar porphyrins show large Stokes shifts, decreased yields and smaller excited singlet state lifetimes.

Extensive X-ray studies of six Ni(II) tetraphenylporphyrins (NiTPP) probe into the effects of beta-substituents on their conformation. The studies reveal nonplanar saddle conformations for four of the NiTPPs in solution, powder and crystal forms, planar shapes for two NiTPPs in powder form and, for one of the latter two, a planar shape in solution as well. The results suggest that porphyrin and hydroporhyrin structures are highly flexible in vitro and in vivo and that they may change their conformations in response to steric influences such as from beta-substituents.

The nickel and copper complexes of dodecasubstituted porphyrins bearing aryl groups at the meso positions and propano rings at the pyrrole beta positions were investigated. It was shown that the nickel complex NiTC5T(3,4,5-OMeP)P exhibits a nonplanar conformation, while the corresponding copper complex CuTC5T(3,4,5-OMeP)P is planar. The usefulness of spectroscopic probes of porphyrin nonplanarity is also investigated. The identification of the planar dodecasubstituted porphyrin indicates the flexibility of the tetrapyrrole macrocycle.

A study is made on the syntheses, structures and spectroscopic properties of some highly substituted porphyrins in an effort to create model compounds for the evaluation of theoretical models of porphyrin nonplanarity. The results indicate the feasibility of preparing dodecaphenylporphyrin and dodecaalkylporphyrins through the use of standard synthetic steps. Other results include the tilting of pyrrole rings, the formation of nonplanar conformations with similar distortion modes and the differentiation of certain distortion modes from the dications and nickel complexes of porphyrins.

The metal dependent electron donor or electron acceptor properties of the microscale four-leaf clover-shaped structures formed by self-assembly of anionic and cationic porphyrin are reported. The results demonstrated that clovers derived from anionic Zn porphyrins (electron donors) and cationic Sn porphyrins (electron acceptors) are photoconductors, but when the metals are reversed in the two porphyrins, the resulting clovers are insulators.

A method is developed for using lipoporphyrin-stabilized nanodroplets of an organic solvent in water as templates to synthesize dendrite Pt nanoshells. A key feature of the method is the use of a tin-porphyrin complex both as a surfactant that stabilizes the nanoscale benzene droplets and as a photocatalyst to initiate Pt reduction onto the surfaces of the nanodroplets.

Density functional theory (DFT) and the DFT+U technique are applied to study the adsorption of transition metal porphine molecules on atomistically flat Au(111) surfaces. The binding can be partially reversed by applying an electric potential and this method can be used as general method for modeling first-row transition metal ion complexes in condensed-matter setting.

Polarized resonance Raman spectroscopy is utilized to explore the relationship between the Raman activity of out-of-plane modes and the out-of-plane deformations of different synthetic nickel prophyrins. The coupling strengths of the out-of-plane modes are determined, and the results indicate that some of these modes can be used as a quantitative probe to determine the ruffling deformation of porphyrins with alkyl substituents at their meso positions.

The effects of ruffling on the axial ligation properties of a series of nickel(II) tetra(alkyl)porphyrins are investigated with UV-visible absorption spectroscopy, resonance Raman spectroscopy, X-ray crystallography, classical molecular mechanics calculations and normal-coordinate structural decomposition analysis. The study suggests that molecular mechanics calculations might aid in designing nano-devices with appropriate conformations and switching characteristics.

Nanotubes containing a Sn porphyrin are photocatalytic and can reduce metal ions from aqueous solution. It is investigated that whether the Sn porphyrins in the nanotubes makes the tubes photocatalytic, as Sn porphyrins are known to be good photocatalysts in homogeneous solutions.

The study presented reveals that porphyrin nanotubes can be ionic self-assembly of two oppositely charged porphyrins in aqueous solution. These nanotubes represent a new class of porphyrin nanostructures, for which the molecular building blocks could be altered to control their structural and functional properties.

The ground- and excited-state metal-ligand dynamics of nonplanar nickel(II)2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (NiDPP) and two fluorinated analogues are investigated using static and time-resolved absorption spectroscopy in toluene and in ligating media that differ in basicity, aromaticity, and steric encumbrance. The results demonstrate the sensitivity with which the electronic and structural characteristics of the macrocycle, substituents, and solvent (ligand) can govern the photophysical and photochemical properties of nonplanar porphyrins and open new avenues for exploring photoinduced ligand association and dissociation behavior.

Research has been conducted on aryl-porphyrin rotational barrier. The authors have used NMR spectroscopy in examining the relationship between this barrier and the core substituent M in some octaphenylporphyrins.

We have measured the polarized Raman cross sections and depolarization ratios of 16 fundamental modes of nickel octaethyltetraphenylporphyrin in a CS2 solution for 16 fundamental modes, i.e., the A1g-type vibrations ν1, ν2, ν3, ν4, ν5, and [lowercase_phi_synonym]8, the B1g vibrations ν11 and ν14, the B2g vibrations ν28, ν29, and ν30 and the antisymmetric A2g modes ν19, ν20, ν22, and ν23 as function of the excitation wavelength. The data cover the entire resonant regions of the Q- and B-bands. They were analyzed by use of a theory which describes intra- and intermolecular coupling in terms of a time-independent nonadiabatic perturbation theory [E. Unger, U. Bobinger, W. Dreybrodt, and R. Schweitzer-Stenner, J. Phys. Chem. 97, 9956 (1993)]. This approach explicitly accounts in a self-consistent way for multimode mixing with all Raman modes investigated. The vibronic coupling parameters obtained from this procedure were then used to successfully fit the vibronic side bands of the absorption spectrum and to calculate the resonance excitation profiles in absolute units. Our results show that the porphyrin macrocycle is subject to B2u-(saddling) and B1u-(ruffling) distortions which lower its symmetry to S4. Thus, evidence is provided that the porphyrin molecule maintains the nonplanar structure of its crystal phase in an organic solvent. The vibronic coupling parameters indicate a breakdown of the four-orbital model. This notion is corroborated by (ZINDO/S) calculations which reveal that significant configurational interaction occurs between the electronic transitions into |Q>- and |1B>-states and various porphyrin→porphyrin, metal→porphyrin, and porphyrin→metal transitions. The intrastate coupling parameters are used to estimate the excited electronic states’ displacements along the normal coordinates with respect to the ground state and their contributions to the reorganization energy. It turns out that the |B>-state is predominantly affected by symmetric A1g-displacements, whereas the |Q>-state is subject to A2g, B1g, and B2g displacements of its equilibrium configuration. While the former is induced by the combined effect of ruffling and saddling, the latter arises from Jahn–Teller coupling within the degenerate states. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The photoexcitation of the nonplanar porphyrin 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (H2DPP) are examined using transient absorption spectroscopy. It is shown that H2DPP undergoes conformational/vibrational relaxation and equilibration in the (super 1)[pi,pi(super *)] excited state that takes ~10 ps, and that this process is not observed for the nominally planar 5,10,15,20-tetraphenylporphyrin system.

The synthesis of discrete free-standing porphyrin nanosheets is described by using a reprecipitation method. The unique morphology, photocatalytic properties, and large surface areas have indicated that they can be used in electronics, photonics and catalytic systems.