Electrochemical behavior of the tetracationic porphyrins and (original) (raw)
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Spectrochimica Acta Part A: Molecular Spectroscopy, 1992
Abatraet-A series of water-soluble zinc porphyrins, ZnTPPS, ZnTPPC and ZnTPPOH, have been synthesized. Their absorption, emission, singlet and triplet state quenching by electron acceptors like MVZf and 1,5-AQDS*-have been studied in homogeneous aqueous solutions and bound to a PVP matrix. Binding constants for the systems under study do not vary much and give a low value for AC'=-13.37 kJM-'. However, the number of monomer units required for binding any individual porphyrin species varies with the size of the molecule. It appears that these water-soluble porphyrins are embedded in hydrophobic pockets in the polymer matrix and are only partially available to outside quenchers like MV'+ and 1,5-AQDS*-From flash photolysis studies, formation of porphyrin radical cations and quencher anions is observed. Porphyrin cations are long-lived and are also formed on self-quenching and by disproportionation reactions in the absence of quencher. ZnTPPOH behaves differently.
Electrochemical and spectroelectrochemical characterization of meso-tetra-alkyl porphyrins
Electrochimica Acta, 2005
A series of three meso-tetra-alkyl porphyrins (H 2 TAPs) were synthesised and their electrochemical properties were studied in dichloromethane containing either tetra-butyl ammonium perclorate (TBAP) or tetra-butyl ammonium hexafluorophosphate TBA(PF 6) as supporting electrolyte (SE) by cyclic voltammetry and in situ UV/vis spectroelectrochemistry. Values of E 1/2 for the recorded four redox processes of these porphyrins and of the meso-tetra-phenyl porphyrin (H 2 TPP) on glassy carbon and platinum were measured and compared. The redox data collected on the first oxidation and the first reduction processes predict that the value of (LUMO − HOMO) for the H 2 TAPs is lower than for meso-tetra-phenyl porphyrin and, therefore, that the first Q band of the electronic spectra of the H 2 TAPs is red shifted relatively to the same band in the spectrum of H 2 TPP; this shift was indeed found. The second oxidation process of the H 2 TAPs is influenced by the supporting electrolyte used and the dication then formed is consumed by an irreversible chemical reaction. The species produced in this reaction is irreversibly reduced at a considerably lower potential. The electrochemical and spectroelectrochemical data collected are consistent with the occurrence of structural distortion in the macrocycle rings of the H 2 TAPs.
Unusual spectral and electrochemical properties of azobenzene-substituted porphyrins
Electrochimica Acta, 2012
A series of azobenzene-substituted porphyrin derivatives, MPA n (M = H 2 , Zn; n = 1, 2, 4), has been prepared. These compounds were characterized by spectral and electrochemical methods. The Soret and Q bands of ZnPA n were red-shifted along with the increase of Q-band intensity ratio (ε˛/εˇ) as the substitution of azobenzene increased. Addition of imidazole towards ZnPA n caused a significant increase in Q band intensity ratio. A noteworthy characteristic is that the Q band intensity ratio was reversed (>1.0) by imidazole ligation for ZnPA 4. Additionally, cyclic voltammetry of H 2 PA n exhibited anodic shift of the first oxidation potential but cathodic shift for the second oxidation potential for porphyrin free bases as azobenzene number increased. According to DFT calculation, the unusual features in UV-vis spectra and redox potentials arised mainly due to the intramolecular-conjugation between porphyrin and azobenzene.
The Journal of Physical Chemistry B, 2005
The photophysical properties of excited singlet states of zinc tetra-(p-octylphenyl)-porphyrin in 5-25-nm-thick films spin-coated onto quartz slides have been investigated by optical spectroscopy. Analysis of the polarized absorption spectra using a dipole-dipole exciton model with two mutually perpendicular transition dipole moments per molecule shows that the films are built from linear aggregates, i.e., stacks with a slipped-deck-of-cards configuration. The molecular planes of the porphyrins in the stacks are found to be perpendicularly oriented with respect to the substrate plane. Assuming a value of 2-3 for the dielectric constant of the film, from the excitonic shift, an angle of 44 degrees +/- 3 degrees and an interplanar distance of 0.35-0.36 nm between adjacent porphyrins are calculated, close to the ground-state geometry in solution. The ordering in these films was further investigated by the effects of various solvents and temperature annealing. Spin-coating from toluene as a solvent results in highly ordered films, and annealing of these films has little effect on their absorption spectra. However, spin-coating from chloroform or pyridine or exposure of the films to these solvents in their vapor phases changes their ordering presumably due to incorporation of residual solvent molecules. Annealing yields absorption spectra identical to those of films spin-coated from toluene. The absorption spectra are insensitive to atmospheric moisture, in contrast to those of zinc tetraphenylporphyrin films lacking octyl substituents.
Inorganica Chimica Acta, 2005
The spectroscopic and electrochemical properties of two isomeric forms of the supramolecular species [l-(H 2 TPyP){Ru-(bpy) 2 Cl} 4 ] 4+ (H 2 TPyP = 5,10,15,20-tetra(3-or 4-pyridyl)porphyrin, bpy = 2,2 0 -bipyridine) have been compared and consistently interpreted with the aid of molecular orbital calculations. In these complexes, the HOMO and LUMO levels are predominantly localized in the ruthenium complexes and porphyrin ring, respectively. There is an extensive mixing of the wave functions of both components in other MOs, however, and their contributions are reflected in the spectroelectrochemical and spectroscopic behavior. For example, the electronic mixing is enough to allow the energy-transfer from the peripheral complexes to the porphyrin ring, as well as the appearance of a Ru II (dp) ! H 4 P(pp*) charge-transfer band at 700 nm in the bis-protonated [l-(H 4 TPyP){Ru-(bpy) 2 Cl} 4 ] 4+ species, showing the strong stabilization of the porphyrin LUMO levels.
Synthesis and spectroscopic properties of a soluble semiconducting porphyrin polymer
Physical chemistry chemical physics : PCCP, 2014
A semiconducting porphyrin polymer that is solution processable and soluble in organic solvents has been synthesized, and its spectroscopic and electrochemical properties have been investigated. The polymer consists of diarylporphyrin units that are linked at meso-positions by aminophenyl groups, thus making the porphyrin rings an integral part of the polymer backbone. Hexyl chains on two of the aryl groups impart solubility. The porphyrin units interact only weakly in the ground electronic state. Excitation produces a local excited state that rapidly evolves into a state with charge-transfer character (CT) involving the amino nitrogen and the porphyrin macrocycle. Singlet excitation energy is transferred between porphyrin units in the chain with a time constant of ca. 210 ps. The final CT state has a lifetime of several nanoseconds, and the first oxidation of the polymer occurs at ca. 0.58 V vs. SCE. These properties make the polymer a suitable potential excited state electron dono...
UV-VIS spectroscopy study on porphyrin nanostructures formed by electrostatic interaction
Ife Journal of Science, 2016
Porphyrin nanostructure were fabricated by ordinary electrostatic self - assembly and phase transfer electrostatic self–assembly and characterized using ultraviolet-visible spectrophotometry only. For ordinary electrostatic self-assembly, aqueous solution of the negatively-charged porphyrins - meso-tetra(4-phenylsulphonic) porphyrin (TPPS 4 4- ) and meso-tetra(4-carboxyphenyl) porphyrin (TCPP 4- ) (TPPS/TCPP) was mixed with aqueous solution of the positively-charged metalloporphyrins - meso-tetra(4-pyridyl) porphyrin [MTPyP (M=Zn, Ni, Co and Mn)]. In the case of phase transfer technique, the aqueous solutions of the negativelycharged porphyrins were (TPPS/TCPP) added to dichloromethane solution of MTPyP. The aqueous and organic phases were studied separately. The electronic spectra of TPPS-MTPyP using ordinary electrostatic self-assembly technique showed the typical J-aggregation influenced by TPPS with bands around 492 nm and 708 nm. These bands were absent in the case of TCPP-MTPy...
Preparations and Electrochemical Characterizations of Conductive Porphyrin Polymers
The Journal of Physical Chemistry C, 2015
5,10,15,20-Tetrakis(4-aminophenyl)porphyrin (TAPP) undergoes oxidative polymerization to form electronically conductive, nanofibrous structures in which the porphyrin units are linked by phenazine bridges. Polymerizations by chemical oxidation, electrochemical oxidation, and interfacial oxidative polymerization are described. Poly-TAPP (pTAPP) films have been characterized using scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and UV−vis spectroscopy. The polymer morphology is consistently nanofibrous, with some differences depending on the specific synthetic method. The polymer films show distinctive electrochromism at different redox and protonation states. A Pourbaix diagram correlates the proposed redox and protonation states of the polymer with applied potential, pH, and perceived color of the film. pTAPP shows the lowest resistance to oxidative doping/dedoping at low pH and potentials between +0.4 and +0.5 V vs Ag/AgCl.
Journal of Coordination Chemistry, 2019
Methoxy-isoporphyrins of zinc [5,10,15,20-tetrakis(4-sulfonatophenyl)]porphyrin, ZnTSPP (1a) and zinc [5,10,15,20-tetrakis(4-carboxyphenyl)]porphyrin, ZnTCPP (1b) have been synthesized and characterized using standard spectroscopic techniques (Uv-visible, ARTICLE HISTORY