Cofacial Diporphyrins Research Articles

Ligand Modifications for Tailoring the Binuclear Microenvironments in Schiff-Base Calixpyrrole Pacman Complexes

The synthesis and structures of two new octadentate, Schiff-base calixpyrrole macrocycles are presented in which modifications at the meso-substituents (L(1)) or the aryl spacer between the two pyrrole-imine donor compartments (L(2)) are introduced. The outcomes of these changes are highlighted in the structures of binuclear Pacman complexes of these macrocycles, [M(2)(L(1))] and [M(2)(L(2))]. Both palladium and cobalt complexes of the fluorenyl-meso-substituted macrocycle H(4)L(1) adopt rigid, but laterally twisted geometries with enclosed bimetallic microenvironments; a consequence of this spatial constraint is an exo-exo-bonding mode of pyridine in the dicobalt complex [Co(2)(py)(2)(L(1))]. In contrast, the use of an anthracenyl backbone between the two donor compartments (H(4)L(2)) generates a binuclear palladium complex in which the two PdN(4) environments are approximately cofacial and separated by 5.3 A, so generating a bimetallic complex that is structurally very similar to binuclear compounds of cofacial diporphyrins.

Fine tuning of the photophysical properties of cofacial diporphyrins via the use of different spacers

The crystal and molecular structures of two unmetallated diporphyrin species using the biphenylene and dibenzofuran spacers, H 4(DPB) and H 4(DPO), respectively (DPB 4−=1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]biphenylene; DPO 4−=4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzofuran), are reported. These data are compared to their literature metallated analogs, stressing on the properties related to the flexibility of the ligands, π⋯π and M⋯M interactions. In addition, the lowest energy fluorescence properties of these non-phosphorescent diporphyrin compounds as well as three other related species, H 4(DPA), H 4(DPX), and H 4(DPS) (DPA 4−=1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]anthracene; DPX 4−=4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene; DPS 4−=4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzothiophene), have been examined both at room temperature in 2-MeTHF in the presence of Ar, air and O 2, and at 77 K. In all cases, the fluorescence arises from the 1Q(ππ*), and the photophysical data at 77 and 298 K under Ar atmosphere correlate readily with the molecular geometry of these pincer ligands, where the non-radiative rate constants increase as the interplanar distances decrease. In the presence of dioxygen in solution, both the fluorescence lifetimes and quantum yields decrease as expected for quenching, with the second-order rate constants for bimolecular deactivation ( k Q) ranging from 0.9×10 10 to 1.7×10 10 s −1 M −1. The H 4(DPB) compound exhibits the lowest k Q indicating lesser ability for O 2 to interact with the interior of the diporphyrin cavity.

Reactivity toward Dioxygen of Dicobalt Face-to-Face Diporphyrins in Aprotic Media. Experimental and Theoretical Aspects. Possible Mechanistic Implication in the Reduction of Dioxygen

The reactivity toward dioxygen of two series of dicobalt cofacial diporphyrins in solution in an aprotic solvent is described. Some of these compounds are efficient electrocatalysts for the four-electron reduction of dioxygen when adsorbed on a graphite electrode immersed in aqueous acid. Their electrochemical and spectroscopic (UV−vis, EPR) behavior in solution shows that, contrary to what is observed with cobalt monomers, the neutral [PCoII CoIIP] (1) (P stands for a porphyrin ring) form does not react with dioxygen. Uniquely the one- and two-electron-oxidized forms of the dimer, [PCoII·CoIIP]+ (1+) and [PCoII---CoIIP]2+ (12+), respectively, reversibly bind dioxygen, giving two complexes, 2 and 3, at room temperature and in the absence of a good axial ligand. The stability constants of the two O2 complexes have been measured spectrophotometrically and/or electrochemically, and prove to be remarkably high. As a whole, the present O2 binding processes appear unprecedented as basically different in many respects from the process classically described in the case of cobalt monomers. Extended Hückel molecular orbital (EHMO) calculations, based on the crystal structure of the Co2FTF4 dimer in its uncomplexed form (Co−Co distance 3.42 Å), show that, in the absence of very important deformations of its structure, the only possible geometry for the O2 complex of the two-electron-oxidized derivative [PCo−O2−CoP]2+ (3) is the μ-η2:η2-peroxo structure. The calculated corresponding electronic diagram affords a rationale for most of the experimentally observed properties. Specifically, the O2 complex of the one-electron-oxidized form [PCo−O2•−CoP]+ (2), the reduced form of complex 3, should be considered as a species in which the O2 moiety is further reduced, at least partially, as compared to its peroxo state in 3, i.e., consequently in an oxidation state intermediate between peroxo (−1) and oxo (−2). Preliminary results indicate that this species reacts with one proton, while the two-electron-oxidized O2 complex 3 is resistant to protonation. The possible implications of these specific properties of the dicobalt dimers in the four-electron reduction mechanism of O2 are discussed, and structural and mechanistic similarities with bioinorganic dinuclear sites appear significant.

Electrochemical and spectroscopic behavior of dicobalt cofacial diporphyrins. The redox sites revisited

Abstract The electrochemical behavior of dicobalt cofacial porphyrins is reported and the EPR and UV-Vis spectra of their oxidized forms are described. The results are discussed in terms of a comparison with the properties of the same complexes bearing non-electroactive metals, which have been described recently. On the basis of UV-Vis spectrophotometry, EPR and electrochemical criteria, an original formal writing is offered for the oxidation pathway of the dicobalt porphyrins in PhCN. It is proposed that the first oxidation process concerns the π-rings. the second is the oxidation of the cobalt (II) into cobalt (III) and a third one the second oxidation of the π-rings. Based on the X-ray structure of the Co2FTF4 diporphyrin, extended Huckel MO calculations can provide a theoretical basis for the electrochemical and spectroscopic behavior. This arises from crossings of the π-ring ligand and (cobalt) metallic levels due to a combination of π−π and d-d electronic interactions between the two moieties of the dimers. A steric effect is also emphasized: the size of the interporphyrin cavity exerts a selectivity as regards internal ligation. The present findings afford a completion of the so-called ‘cofacial effect’ of intramolecular interactions in dimers proposed in a previous paper.

Electrocatalytic Reduction of Dioxygen by Diruthenium Cofacial Diporphyrins Axially-Bound to a Gold-Supported, Self-Assembled Monolayer

A gold-supported, self-assembled monolayer containing imidazole termini provides axial binding sites for the diruthenium cofacial diporphyrins (μ-N2)Ru2(DPA)(CH3CN) and (μ-N2)Ru2(DPB)(CH3CN). These electrode-bound molecules electrocatalytically reduce dioxygen in a well-characterized environment. The SAM environment makes it easier to study the effect that the eletrode−catalyst interactions are having on the catalysis compared with those of the traditional environment of EPGE.

Synthesis and characterization of a superoxo complex of the dicobalt cofacial diporphyrin [(.mu.-O2)Co2(DPB)(1,5-diphenylimidazole)2][PF6], the structure of the parent dicobalt diporphyrin Co2(DPB), and a new synthesis of the free-base cofacial diporphyrin H4(DPB)

Chemical oxidation of the dicobalt cofacial diporphyrin Co 2 II / II (DPB), followed by exposure to dioxygen affords the bridged superoxo complex [(μ-O 2 )Co 2 (DPB)][PF 6 ]. This μ-superoxo complex has been implicated in possible mechanisms of four-electron dioxygen reduction by dicobalt cofacial diporphyrins but has not been isolated and fully-characteized previously.

Resonance Raman spectra of dioxygen adducts of pillared dicobalt cofacial diporphyrins

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTResonance Raman spectra of dioxygen adducts of pillared dicobalt cofacial diporphyrinsLeonard M. Proniewicz, Junichi Odo, Joanna Goral, Chi K. Chang, and Kazuo NakamotoCite this: J. Am. Chem. Soc. 1989, 111, 6, 2105–2110Publication Date (Print):March 1, 1989Publication History Published online1 May 2002Published inissue 1 March 1989https://doi.org/10.1021/ja00188a025RIGHTS & PERMISSIONSArticle Views120Altmetric-Citations29LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (674 KB) Get e-Alerts Get e-Alerts

Crystal and molecular structure of anthracene and biphenylene pillared cofacial diporphyrins

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCrystal and molecular structure of anthracene and biphenylene pillared cofacial diporphyrinsJ. P. Fillers, K. G. Ravichandran, I. Abdalmuhdi, A. Tulinsky, and C. K. ChangCite this: J. Am. Chem. Soc. 1986, 108, 3, 417–424Publication Date (Print):February 1, 1986Publication History Published online1 May 2002Published inissue 1 February 1986https://doi.org/10.1021/ja00263a011RIGHTS & PERMISSIONSArticle Views518Altmetric-Citations91LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (887 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Synthesis and geometry determination of cofacial diporphyrins. EPR spectroscopy of dicopper diporphyrins in frozen solution

Synthesis and geometry determination of cofacial diporphyrins. EPR spectroscopy of dicopper diporphyrins in frozen solution

Nonbonding steric effect on carbon monoxide and oxygen binding to hemes. Kinetics of ligand binding in iron-copper cofacial diporphyrins and strapped hemes

Nonbonding steric effect on carbon monoxide and oxygen binding to hemes. Kinetics of ligand binding in iron-copper cofacial diporphyrins and strapped hemes

Photoelectrochemical properties of metalloporphyrins

The photovoltaic responses of meso tetraphenyl-, meso tetra-propyl- and octaethyl-porphyrins, porphines, chlorins, cofacial diporphyrins and mesoporphyrin IX diesters were investigated using two cell configurations: Al| Porphyrin |Ag, and Al| Porphyrin | Fe(CN)6−3, Fe(CN)6−4 |Pt. We found (1) that the Al–porphyrin interface is photoactive: the action spectra closely follow the absorption spectra of the porphyrins, and this interface is best described as a semiconductor–insulator–metal diode consisting of porphyrin |A12O3 |Al; (2) that within a homologous series, in which the porphyrin skeleton is fixed but the metal is varied, the quantum yields parallel the ease of oxidation of the porphyrin in nonaqueous solvents. The more easily oxidised compounds exhibit the higher quantum yields; (3) no obvious correlations are found with the luminescent properties of the porphyrins in solution; (4) the morphology of the films influences the quantum yields: amorphous films are better than microcrystalline ones; and (5) the most efficient cells reach quantum yields of ∼0.2 and energy efficiencies of ∼1% for monochromatic light at the peak of the action spectrum in the region of 400–450 nm.

Electron transfer reactions in cofacial diporphyrins

Abstract Optical difference spectra consonant with electron transfer from a magnesium porphyrin to a free base porphyrin are obtained following picosecond excitation of cofacial diporphyrins covalently linked approximately 4Aapart. The charge-transfer species decays with a lifetime of 620 ± 20 ps.

ChemInform Abstract: STACKED DOUBLE‐MACROCYCLIC LIGANDS. II. SYNTHESIS OF COFACIAL DIPORPHYRINS

Chemischer InformationsdienstVolume 9, Issue 19 Heterocyclic Compounds ChemInform Abstract: STACKED DOUBLE-MACROCYCLIC LIGANDS. II. SYNTHESIS OF COFACIAL DIPORPHYRINS C. K. CHANG, C. K. CHANGSearch for more papers by this authorM. S. KUO, M. S. KUOSearch for more papers by this authorC. B. WANG, C. B. WANGSearch for more papers by this author C. K. CHANG, C. K. CHANGSearch for more papers by this authorM. S. KUO, M. S. KUOSearch for more papers by this authorC. B. WANG, C. B. WANGSearch for more papers by this author First published: May 9, 1978 https://doi.org/10.1002/chin.197819208AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume9, Issue19May 9, 1978 RelatedInformation

Stacked double‐macrocyclic ligands III. Spectral properties of cofacial diporphyrins as a function of the inter‐chromophore separation

AbstractThree homologous cofacial diporphyrins that have interplanar distances ranging from 6.4Å to 4.2Å have been synthesized. Their absorption and emission spectra revealed strong exciton coupling in the diporphyrin. Magnesium complexes of diporphyrins were studied and their application as a model for P700 photoactive center was discussed.