Journal of Porphyrins and Phthalocyanines

The splitting of water into its constituent elements is an important solar fuels conversion reaction for the storage of renewable energy. For each of the half reactions of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), multiple protons and electrons must be coupled to avoid high-energy intermediates. To understand the mechanistic details of the PCET chemistry that underpins HER and OER, we have designed hangman porphyrin and corrole catalysts. In these hangman constructs, a pendant acid/base functionality within the secondary coordination sphere is "hung" above the macrocyclic redox platform on which substrate binds. The two critical thermodynamic properties of a PCET event, the redox potential and pK_a may be tuned with the macrocycle and hanging group, respectively. This review outlines the synthesis of these catalysts, as well as the examination of the PCET kinetics of hydrogen and oxygen evolution by the hangman catalysts. The insights provided by these systems provide a guide for the design of future HER and OER catalysts that use a secondary coordination sphere to manage PCET.

This mini-review presents a recent development of a new function of heme as a signaling molecule especially in the regulation of gene expression. Heme is biosynthesized as a prosthetic group for heme proteins, which play crucial roles for respiration, photosynthesis, and many other metabolic reactions. In some bacteria, exogenous heme molecules are used as a heme or an iron sources to be uptaken into cytoplasm. As free heme molecules are cytotoxic, the intracellular concentrations of biosynthesized or uptaken heme should be strictly controlled. In this mini-review, we summarize the biochemical and biophysical properties of the transcriptional regulators and heme-sensor proteins responsible for these regulatory systems to maintain heme homeostasis.

This review is devoted to porphyrinoids with N-arylamino groups tethered directly to their meso positions, the study of which has significantly progressed in the past two decades. After a brief introductory description, various synthetic procedures for these compounds are described. The third section focuses on their photochemical and electrochemical properties, and reviews the synergetic effects that arise between the porphyrinoids and the N-arylamino groups. Potential applications are then discussed, focusing on dye-sensitized solar cells (DSSCs).

In this mini-review, we have highlighted our works on metal complexes having saddle-distorted dodecaphenylporphyrin (DPP) and its derivative as ligands in the light of enhancement of the Lewis acidity of a metal center coordinated by the porphyrin. The important point through this mini-review is ill-overlap of the out-of-plane lone pairs of pyrrole nitrogen atoms with σ-orbitals of the metal center bound to the saddle-distorted porphyrin core. The enhanced Lewis acidity of the central metal ions enabled us to construct stable molecular complexes through axial coordination using metal–DPP (M(DPP)) moieties (M = Mo^V or Sn^IV) and molecular or ionic entities with Lewis-basic coordination sites, including Keggin-type polyoxometallates (POM), which are known to have weak Lewis basicity and thus hard to coordinate to metal ions. A discrete 1:2 complex with a Ru-substituted POM performs catalytic substrate oxidation reactions in organic solvents. A 1:1 complex between Sn^IV(DPP) and a Keggin-type POM exhibited photoinduced electron transfer, in which the Sn^IV(DPP) moiety acts as an electron donor and the POM as an electron acceptor. Besides POM, other electron acceptors, including μ₃-oxo trinuclear Ru^III clusters and anthraquinone, having carboxyl groups as a linker unit also formed stable complexes with DPP-metal complexes as axial ligands to perform photoinduced electron transfer. Successful photoreactions of the M(DPP)-acceptor complexes are mainly enabled by the enhanced Lewis acidity of the DPP-metal complexes for the stabilization of the assemblies and also by lowering the oxidation potential of the porphyrin ligand to gain larger driving force of electron transfer to form an electron-transfer state with avoiding intersystem crossing. The stability and photochemical behavior are in sharp contrast to those for metal complexes with planar porphyrins as ligands.

This review summarizes research on the electrochemical and photochemical reduction of CO₂ using a variety of iron and cobalt porphyrins, phthalocyanines and related complexes. Metalloporphyrins and metallophthalocyanines are visible light absorbers with extremely large extinction coefficients. However, yields of photochemically-generated active catalysts for CO₂ reduction are typically low owing to the requirement of a second photoinduced electron. This requirement is not relevant to the case of electrochemical CO₂ reduction. Recent progress on efficient and stable electrochemical systems includes the use of FeTPP catalysts that have prepositioned phenyl OH groups in their second coordination spheres. This has led to remarkable progress in carrying out coupled proton-electron transfer reactions for CO₂ reduction. Such ground-breaking research has to be continued in order to produce renewable fuels in an economically feasible manner.

Guanine-rich single-stranded nucleic acids self-assemble into G-quadruplex nanostructures (predominately in the presence of K⁺-ions). Metalloporphyrins bind to the G-quadruplex nanostructures to form supramolecular assemblies exhibiting unique catalytic, electrocatalytic and photophysical properties. This paper addresses the advances in the characterization and the implementation of the metalloporphyrin/G-quadruplexes complexes for various applications. Out of the different complexes, the most extensively studied complexes are the hemin/G-quadruplex horseradish peroxidase-mimicking DNAzyme and the Zn(II)-protoporphyrin IX-functionalized G-quadruplex. Specifically, the hemin/G-quadruplex was found to act as a catalyst for driving different chemical transformations that mimic the native horseradish peroxidase enzyme, and, also, to function as an electrocatalyst for the reduction of H₂O₂. Also, the hemin/G-quadruplex stimulates interesting photophysical and photocatalytic processes such as the electron-transfer quenching of semiconductor quantum dots or the chemiluminescence resonance energy transfer to semiconductor quantum dots. Alternatively, Zn(II)-protoporphyrin IX associated with G-quadruplexes exhibit intensified fluorescence properties. Beyond the straight forward application of the metalloporphyrin/G-quadruplexes as catalysts that stimulate different chemical transformations, the specific catalytic, electrocatalytic and photocatalytic functions of hemin/G-quadruplexes are heavily implemented to develop sophisticated colorimetric, electrochemical, and optical sensing platforms. Also, the unique fluorescence properties of Zn(II)-protoporphyrin IX-functionalized G-quadruplexes are applied to develop fluorescence sensing platforms. The article exemplifies different sensing assays for analyzing DNA, ligand-aptamer complexes and telomerase activity using the metalloporphyrins/G-quadruplexes as transducing labels. Also, the use of the hemin/G-quadruplex as a probe to follow the operations of DNA machines is discussed.

Axial ligands play a dominating role in determining the electronic structure and reactivity of iron porphyrin active sites and synthetic models. Several properties unique to the cysteine bound heme enzyme, cytochrome P450, is attributed to the "push effect" of the thiolate axial ligand. In this mini-review the ground state electronic structure of iron porphyrins with imidazole, phenolate and thiolate complexes, derived using a combination of spectroscopy and DFT calculations, are discussed. The differences in kinetics and selectivity of oxygen reduction reaction (ORR), catalyzed by these iron porphyrin complexes with different axial ligands, help elucidate the varying push effects of the different axial ligands on oxygen activation by ferrous porphyrin. The spectroscopic and kinetic data help to develop a quantitative understanding of the "push effect" and, in particular, the electrostatic and covalent contributions to it.

This review article briefly describes: (a) the advantages in developing multifunctional nanoparticles for cancer-imaging and therapy, (b) the advantages and limitations of most of the porphyrin-based compounds in fluorescence imaging and photodynamic therapy (PDT), (c) problems associated with current Food and Drug Administration (FDA) approved photosensitizers, (d) challenges in developing in vivo target-specific PDT agents, (e) development of porphyrin-based nuclear-imaging agents (PET, SPECT) with an option of PDT, (f) the importance of light dosimetry in PDT, (g) the role of whole body or local hyperthermia in enhancing tumor-uptake, tumor-imaging and phototherapy and finally, (h) the advantages of photosensitizer-gold nanocages (Ps-Au NC) in photoacoustic and PDT.

A tetrapyrrolic macrocycle containing ethenylene and dioxyphenylene bridges was obtained through the reaction of a dipyrrin-DDQ adduct with triethylamine. The structure of the macrocycle was elucidated by X-ray diffraction analysis. The macrocycle exhibited solvent-dependent absorption spectra due to intramolecular charge transfer interactions.

We synthesized for the first time a push–pull porphyrin dye bearing two diarylamino groups and two carboxyphenylethynyl groups as electron-donating and electron-withdrawing anchoring groups, respectively. The absorption spectrum displayed broad and red-shifted absorption, achieving panchromic light-harvesting in visible and NIR regions. Introduction of multiple push–pull groups into meso-positions is a promising strategy for the rational design of porphyrin sensitizers for light-harvesting applications. The preliminary photovoltaic performance is moderate (3.0%), but the extensive photocurrent generation matches with the excellent light-harvesting ability. Further modulation of the photovoltaic properties of porphyrin DSSCs will be possible by suitable selection of electron-donating and electron-withdrawing groups as well as introduction of the substituents into the porphyrin core.

The first example of a tungsten(V) corrole complex, (Mes₂(p-OMePh)corrole)WCl₂, has been prepared through a metathesis reaction of a lithium corrole (Mes₂(p-OMePh)corrole)Li₃ ⋅ 6THF and WCl₆. The product constitutes the first example of a tungsten(V) corrole complex synthesized under mild conditions and only the second example of a tungsten corrole complex.

A novel terbium-cobalt porphyrin {[Tb(H₂O)₃][Co(TPPS)]}_n•nH₃O (1) (TPPS = tetra(4-sulfonatophenyl)porphyrin) has been synthesized via a hydrothermal reaction and structurally characterized by X-ray single crystal diffraction. Compound 1 is characterized by a three-dimensional (3-D) porous open framework, which is originated from the Co(TPPS) moieties interconnected by the terbium ions. The fluorescence study shows that compound 1 displays an emission band in the blue region. Nanosecond transient spectra reveals that the fluorescence lifetime is 1.14 ms. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) experiments discovers one reversible wave with E_1/2 = -0.80 V.

A series of dihydroxysilicon phthalocyanines having soluble side chains were synthesized and their bulk-state polymerization capability was investigated. Detailed spectroscopic study of the obtained phthalocyaninato-polysiloxanes revealed that strong electron donating ability and small steric hindrance of the peripheral substituents are the dominant factors to afford high-molecular weight polymers. The polymers show the behaviors of columnar liquid crystal (LC), which is clarified by the presence of clear X-ray diffraction patterns with a hexagonal lattice and birefringent textures in polarized optical microscopy. Because of the siloxane covalent bonds through central silicon atoms, phthalocyaninato-polysiloxanes accommodate one-dimensional phthalocyanine arrays with strong π-electronic couplings, thus exhibiting colmnar LC property even for the derivatives carrying short peripheral chains and leading to the relatively higher density of π-electron systems in the materials. This tendency is different from typical discotic small molecules that require optimum side chain structures for LC formation.

A 2,18-bis(diphenylphosphino)porphyrin ligand undergoes complexation with silver(I) chloride to afford a stable phosphine-silver complex. X-ray crystallographic analysis of the complex revealed a dimeric structure of a 1:2 adduct of the diphosphine and silver(I) chloride, where each phosphorus atom coordinates a silver atom. The four AgCl units construct a distorted cubic cluster with small metallophilic interaction. Variable temperature ³¹P NMR study exhibited a slow ligand exchange process between ¹⁰⁷Ag and ¹⁰⁹Ag at high temperature.

Two porphyrin dyads with the donor-π-acceptor molecular architecture, namely (ZnP)-[triazine-gly]-(H₂PCOOH) and (ZnP)-[triazine-Npip]-(H₂PCOOH), which consist of a zinc-metalated porphyrin unit and a free-base porphyrin unit covalently linked at their peripheries to a central triazine group, substituted either by a glycine in the former or a N-piperidine group in the latter, have been synthesized via consecutive amination substitution reactions of cyanuric chloride. The UV-vis absorption spectra and cyclic-voltammetry measurements of the two dyads, as well as theoretical calculations based on Density Functional Theory, suggest that they have suitable frontier orbital energy levels for use as sensitizers in dye-sensitized solar cells. Dye-sensitized solar cells based on (ZnP)-[triazine-gly]-(H₂PCOOH) and (ZnP)-[triazine-Npip]-(H₂PCOOH) have been fabricated, and they were found to exhibit power conversion efficiency values of 5.44 and 4.15%, respectively. Photovoltaic measurements (J–V curves) and incident photon to current conversion efficiency spectra of the two solar cells suggest that the higher power conversion efficiency value of the former solar cell is a result of its enhanced short circuit current, open circuit voltage, and fill factor values, as well as higher dye loading. This is ascribed to the existence of two carboxylic acid anchoring groups in (ZnP)-[triazine-gly]-(H₂PCOOH), compared to one carboxylic acid group in (ZnP)-[triazine-Npip]-(H₂PCOOH), which leads to a more effective binding onto the TiO₂ photoanode. Electrochemical impedance spectra show evidence that the (ZnP)-[triazine-gly]-(H₂PCOOH) based solar cell exhibits a longer electron lifetime and more effective suppression of charge recombination reactions between the injected electrons and electrolyte.

Novel phosphorus triazatetrabenzcorrole (TBC) tetrasubstituted at the α- and β-positions of the peripheral fused benzene rings with t-butylphenoxy substituents have been prepared and characterized. The effect of the substituents on the electronic structures and optical properties is investigated with TD-DFT calculations and MCD spectroscopy. The optical limiting properties have been investigated to examine whether the lower symmetry that results from the direct pyrrole–pyrrole bond and hence the permanent dipole moment that is introduced result in higher safety thresholds, relative to the values that have been reported for phthalocyanines. The suitability of the compounds for singlet oxygen applications has also been examined.

A design strategy for (porphinato)zinc-based fluorophores that possess large near infrared fluorescence quantum yields is described. These fluorophores are based on a (5,15-diethynylporphinato)zinc(II) framework and feature symmetric donor or acceptor units appended at the meso-ethynyl positions via benzo[c][1,2,5]thiadiazole moieties. These (5,15-bis(benzo[c][1′,2′,5′]thiadiazol-4′-ylethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (4), (5,15-bis[4′-(N,N-dihexylamino) benzo[c][1′,2′,5′]thiadiazol-7′-ylethynyl]-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (5), (5,15-bis([7′-(4″-n-dodecyloxyphenylethynyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (6), (5,15-bis([7′-([7″-(4″ ′-n-dodecyloxyphenyl)benzo[c][1″,2″,5″]thiadiazol-4″-yl]ethynyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (7), 5,15-bis ([7′-(4″-N,N-dihexylaminophenylethynyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (8), and (5,15-bis([7′-(4″-N,N-dihexylaminophenylethenyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (9) chromophores possess red-shifted absorption and emission bands that range between 650 and 750 nm that bear distinct similarities to those of the chlorophylls and structurally related molecules. Interestingly, the measured radiative decay rate constants for these emitters track with the integrated oscillator strengths of their respective x-polarized Q-band absorptions, and thus define an unusual family of high quantum yield near infrared fluorophores in which emission intensity is governed by a simple Strickler–Berg dependence.

As new donor–acceptor hybrids for energy and/or electron transfer, zinc complex and free-base of a porphyrin-quinoidal porphyrin dyad linked by a diphenylethynyl bridge were prepared via Sonogashira and subsequent Takahashi coupling reactions. The quinoidal porphyrin units have two dicyanomethylene groups at the opposite meso-positions. The UV-vis absorption spectra of the dyads were almost linear summations of the absorption spectra of each component in comparison with those of the monomeric reference compounds, indicating very weak electronic interactions between the chromophores at the ground state. Both zinc complex and free-base of the reference porphyrin exhibited fluorescence in the range of ca. 600–700 nm upon photoexcitation, while the quinoidal porphyrin monomers showed no fluorescence. The considerable quenching (more than 99%) of the porphyrin fluorescence in the dyads suggested significant electronic communications between the subunits of the excited state. The electrochemical analysis confirmed that the first oxidations of the dyads occur at the porphyrin units and the first reductions take place at the quinoidal porphyrin units. Femtosecond laser flash photolysis of the zinc dyad with photoexcitation at 393 nm showed both ultrafast (<1 ps) energy and electron transfer from the porphyrin unit to the quinoidal porphyrin one, which processes resulted in the quenching of the porphyrin fluorescence. On the other hand, the free-base dyad underwent only energy transfer.

Two ruthenium(II) carbonyl complexes of porphycene, (carbonyl)(pyridine)(2,7,12,17-tetra-n-propylporphycenato)ruthenium(II) (1) and (carbonyl)(pyridine)(2,3,6,7,12,13,16,17-octaethylpor-phycenato)ruthenium(II) (2), have been structurally characterized by single-crystal X-ray diffraction analysis. Cyclic voltammetry has revealed that the porphycene complexes undergo multiple oxidations and reductions in dichloromethane and the reduction potentials are highly positive compared to porphyrin analogs. UV-light irradiation (400 nm or shorter wavelength region) of a benzene solution of 1 and 2 containing external pyridine leads to dissociation of the carbonyl ligand from the ruthenium(II) centers to give the corresponding bis-pyridine complexes. The identical reaction has been also studied for a porphyrin derivative (carbonyl)(pyridine)(2,3,7,8,12,13,17,18-octaethylporphyriato)ruthenum(II) (3). The first-order kinetic analysis has revealed that the photosubstitution of all of the compounds occurs in the order of 10^-3 s^-1 at 298 K but proceeds faster for complexes of porphycene (1 and 2) than that of porphyrin (3).

We have newly constructed supramolecular photovoltaic cells using inclusion complexes of lithium-ion-encapsulated [60]fullerene (Li⁺@C₆₀) and cyclic porphyrin dimers (M-CPD_Py, M = H₄ and Ni₂). First, supramolecular inclusion complexes of Li⁺@C₆₀ and M-CPD_Py were prepared in MeCN/PhCN (3/1, v/v) by rapid injection method. The molecular aggregates with spherical nanoparticles demonstrated a broad absorption property in the visible region. The macroscopic structures were also estimated to be ca. 200 nm in diameter by transmission electron microscope (TEM) and dynamic light scattering (DLS) measurements. The photoelectrochemical solar cells composed of these assemblies on nanostructured SnO₂ electrode were fabricated by electrophoretic deposition method. The photoelectrochemical behavior of the nanostructured SnO₂ film of supramolecular nanoassemblies of Li⁺@C₆₀ and M-CPD_Py is significantly higher than those of the single component films (Li⁺@C₆₀ or M-CPD_Py) and supramolecular inclusion complexes of pristine C₆₀ and M-CPD_Py.

The protonation and deprotonation reactions for a series N-confused meso-tetraaryl-substituted free-base porphyrins containing electron-donating or electron-withdrawing substituents was monitored in CHCl₃ and DMF by UV-visible spectroscopy during titrations with trifluoroacetic acid or tetra-n-butylammonium hydroxide. The spectroscopic data was also used to calculate equilibrium constants for these reactions. The examined compounds are represented as (XPh)₄NCPH₂, where "NCP" represents the N-confused porphyrin π-conjugated macrocycle and X is a CH₃O, CH₃, H or Clpara-substituent on the four meso-phenyl rings (Ph) of the compound. The porphyrins can exist in two tautomeric forms depending upon the solvent and each tautomer undergoes two stepwise protonation reactions leading to formation of the mono- and bis-protonated porphyrins, [(XPh)₄NCPH₃]⁺ and [(XPh)₄NCPH₄]²⁺. A single step deprotonation is observed for the same compounds in DMF and the product is assigned as [(XPh)₄NCPH]^-. Comparisons are made between UV-visible spectra of the protonated, neutral and deprotonated forms of the porphyrin and the effect of the porphyrin ring substituents and tautomeric form of the neutral porphyrin on the UV-visible spectra and protonation constants is discussed along with data from DFT calculations.

A molecular pentad, comprised of zinc phthalocyanine (ZnPc) with four boron dipyrromethene units (BODIPY) have been examined by femtosecond and nanosecond laser flash photolysis to explore its photoinduced intramolecular events from the excited BODIPY. The geometry optimization showed that the phthalocyanine moiety is completely symmetric and form perfect square planar complex with zinc. The absorption spectrum of ZnPc-BODIPY pentad covers most of the visible region (ca. 300–750 nm), which clearly is an advantage for capturing solar energy. The excitation transfer from the singlet BODIPY to ZnPc is envisioned due to good spectral overlap of the BODIPY emission and ZnPc absorption spectra. Femtosecond laser flash photolysis studies provided concrete evidence for the occurrence of energy transfer from the singlet excited BODIPY to ZnPc in tetrahydrofuran. The kinetic study of energy transfer measured by monitoring the decay of the BODIPY emission revealed fast energy transfer (5.90 × 10¹⁰ s^-1) in the molecular pentad. Since the electron transfer from the singlet ZnPc to BODIPY is thermodynamically not feasible, the singlet ZnPc decayed to populates the triplet ZnPc, in addition to the grounds state. These findings suggest the potential of the examined ZnPc-BODIPY pentad to be efficient photosynthetic antenna in the artificial photosynthetic systems.

Mechanistic aspects of photoinduced charge separation in supramolecular triads, constructed using covalently linked zinc porphyrin-ferrocene(s) dyads — self-assembled via axial coordination to either pyridine or phenylimidazole appended fulleropyrrolidine (Fc_x-ZnP:PyC₆₀ or Fc_x-ZnP:ImC₆₀; x = 1 or 2), has been investigated using femtosecond pump-probe transient spectroscopy. Upon photoexcitation of ZnP, charge separation from ferrocene to ¹ZnP* to yield the initial Fc⁺-ZnP^•-:C₆₀ radical ion-pair or charge separation from ¹ZnP* to C₆₀ to yield the initial Fc-ZnP^•+:C₆₀^•- radical ion-pair, depending upon the ferrocene-zinc porphyrin intermolecular distance, was observed. These radical ion-pairs resulted in the formation of ultimate distantly separated Fc⁺-ZnP:C₆₀^•- radical ion-pairs either via an electron migration (former case) or hole shift (latter case) process. Kinetics of charge separation as a function of spacer connecting the ferrocene and porphyrin, and spacer between the porphyrin and fullerene is reported. In agreement with our earlier study (J. Phys. Chem. B 2004; 108: 11333–11343), the Fc⁺-ZnP:C₆₀^•- radical ion-pair persisted beyond the monitoring time window of our instrument, suggesting charge stabilization in these supramolecular triads.

Photochromic switching of fluorescence emission provides a viable principle to creation of all optical molecular memory. Successful operation of the fluorescence memory requires deliberate control of the energetics between a fluorophore and a photochrome. One essential requirement is that photoexcitation for fluorescence emission does not interfere with the photochromic processes. Gallium(III) corrole complexes outfit the condition because their fluorescence emissions display large Stokes shifts, permitting photoexcitation at the optical window where the photochromism of cis-1,2-dithienylethene is not executed. To demonstrate the capability for fluorescence memory, we prepared molecularly dispersed poly(methyl methacrylate) (PMMA) films of a gallium corrole complex and cis-1,2-dithienylethene. The memory cycle comprising fluorescence readout and reversible photochromic switching of the fluorescence emission is fully reversible without suffering from fatigue during repeated operation. The corresponding fluorescence on/off ratio is greater than those of previous memory based on porphyrins. Fluorescence lifetime measurements employing time-correlated single photon counting techniques reveal occurrence of fast energy transfer (~ 10⁹ s^-1) which is effectively gated by the photochromism.

A Sn(IV)tetraphenylporphyrin (T) has been functionalized with a β-vinyl pyrene (P) and the photophysical properties of the formed dyad (T-P) with its corresponding precursors were studied in three solvents with different polarities using steady-state and time-resolved measurements in ps and fs timescales. When the pyrene moiety is excited at λ_ex = 340 nm, the fluorescence spectroscopy experiments indicate in all the studied solvents, an efficient quenching of the pyrene emission. When excited at either λ_ex = 340 nm or λ_ex = 405 nm, where porphyrin absorbs, a new emissive excited state complex (T-P)* is observed at wavelenghts close to the parent porphyrin emission. The emission is more pronounced in nonpolar hexane showing a mono-exponential decay, but bi-exponential decays are observed in more polar dicloromethane and acetonitrile. When the porphyrin moiety is excited at λ_ex = 425 nm, the fs transient absorption analysis shows two different intermediate species (~ 7–11 ps and 80–100 ps) with broad absorption in the near-IR region. This implies either the existence of two different excited conformers (T-P)*, which decay to the ground state via a charge separated state (CSS), or the formation of the (T-P)* state via the second excited state of the porphyrin moiety, yielding first an excited emissive ^v(T-P)* state, with a lifetime of 80–100 ps.

We substituted strongly electron-withdrawing trifluoromethyl (CF₃) group(s) as heme side chain(s) of human adult hemoglobin (Hb) to achieve large alterations of the heme electronic structure, in order to elucidate the relationship between the oxygen (O₂) binding properties of Hb and the electronic properties of heme peripheral side chains. The obtained results were compared with those of similar studies performed on myoglobin (Mb), e.g. (Nishimura R, Matsumoto D, Shibata T, Yanagisawa S, Ogura T, Tai H, Matsuo T, Hirota S, Neya S, Suzuki A, and Yamamoto Y. Inorg. Chem. 2014; 53: 9156–9165). These two proteins shared the common feature of a decrease in O₂ affinity upon the CF₃ substitution(s). Using the P₅₀ value, which is the partial pressure of O₂ required for 50% oxygenation of a protein, and the equilibrium constant (pK_a) of the "acid-alkaline transition" in the met form of a protein as measures of the O₂ affinity and the electron density of heme Fe atom of the protein, respectively, a linear pK_a-log(1/P₅₀) relationship was demonstrated for the Hb and Mb systems. The native Hb, however, deviated from the pK_a-log(1/P₅₀) relationship, while the native Mb followed it. These results highlighted the significance of the vinyl side chains of the heme cofactor in the functional control of Hb through tertiary and quaternary structural changes upon the oxygenation of the protein.

Zinc-porphyrin(ZnP)–viologen(V²⁺) linked compound containing six methylene group (ZnP(6)V)–silver nanoparticle (AgNP) composite films was fabricated by combining electrostatic layer-by-layer adsorption and the Langmuir–Blodgett method. The incident photo to photocurrent efficiency (IPCE) values of the ZnP(6)V–AgNP composite films are higher than those of the ZnP(6)V films and much higher than those of ZnP derivative films without V²⁺ moiety as a reference. The large increase in the IPCE values of the ZnP(6)V–AgNP composite films likely comes from a combination of localized surface plasmon resonance (LSPR) from AgNPs and photoinduced intramolecular electron-transfer upon linking to a V²⁺ moiety. The photocurrents of the ZnP(6)V–AgNP composite films and the ZnP(6)V films increase upon application of a magnetic field. Magnetic field effects (MFEs) were clearly observed for both ZnP(6)V–AgNP composite films and the ZnP(6)V films. Photocurrents increase with magnetic field under low magnetic fields (B ≤ 150–300 mT) and are constant under high magnetic fields (B > 150–300 mT). MFEs can be explained by a radical pair mechanism. The magnitude of the MFEs in the ZnP(6)V–AgNP composite films is higher than that in the ZnP(6)V films. A remarkable increase in photocurrent for the ZnP(6)V–AgNP composite films was observed because of LSPR from the AgNPs in the presence of a magnetic field when compared with the ZnP(6)V films in the absence of a magnetic field.

Two phthalocyanines (Pcs) with either a zinc or a ruthenium metal at the center of the macrocycle have been functionalized by a cholesteryl oleate moiety. The potential photosensitizers (PSs) for the treatment of cutaneous leishmaniasis have been studied on their photophysical properties and their ability to generate singlet oxygen. These experiments corroborate that solvent mixtures containing variable ratios of THF and water impact the excited state deactivation. The compounds were used preloaded into LDL particles and their phototoxic activity was evaluated in a preliminary way.

Cytochrome P450BM3 functions as a small-alkane hydroxylase upon the addition of perfluorocarboxylic acids (PFs) as decoy molecules. The coupling efficiency (product formation rate per NADPH consumption rate) for the hydroxylation of small alkanes was improved by reducing the reaction temperature to 0°C.

This work reports on the synthesis and characterization of a new gold nanoparticle-zinc phthalocyanine system, AuNP-S(^tBu)₃ZnPc, prepared by a ligand exchange reaction of tetraoctylammonium bromide with a novel unsymmetrically substituted zinc phthalocyanine which contains one thioester group in the peripheral position [AcS(^tBu)₃ZnPc]. The AuNP-S(^tBu)₃ZnPc hybrid was characterized using UV-vis and ¹H NMR spectroscopies. Transmission electron microscopy allowed the estimation of the size, which was calculated to be ~5 nm. AuNPs-S(^tBu)₃ZnPc conjugate showed much lower fluorescence quantum yield values than the AcS(^tBu)₃ZnPc demonstrating either an energy or electron transfer from the ZnPc to the AuNP. The AuNP-S(^tBu)₃ZnPc hybrid has been anchored to a TiO₂ semiconducting layer using lipoic acid. A solid configuration of TiO₂-lipoic acid-AuNP-S(^tBu)₃ZnPc has been prepared by anchoring lipoic acid to the TiO₂ (TiO₂-LA) and introducing later the TiO₂-LA with free thiol groups in a toluene solution of AuNP-S(^tBu)₃ZnPc. We have also observed by UV-vis and fluorescence measurements the importance of the ZnPc in avoiding AuNP aggregation on the TiO₂ surface.

In this report, we have designed and synthesized a novel switching molecule whose fluorescence can be switched via dynamic conformational change between expanded and shrunk states induced by metal complexation and decomplexation. The switching molecule is composed of three kinds of components, namely, a Zn²⁺-porphyrin fluorophore, two quinone quenchers, and their linkers containing a 4,4′-bipyridine moiety. UV-vis and fluorescence titration studies revealed that metal complexation of the bipyridine units with Zn²⁺ ions induced the dynamic structural change of the molecular shape and simultaneous enhancement of fluorescence of the Zn²⁺-porphyrin fluorophore.

Following up on the characterization of a new (heme)Fe^III-superoxide species formed from the cryogenic oxygenation of a ferrous-heme (P^Py)Fe^II (1) (P^Py = a tetraarylporphyrinate with a covalently tethered pyridine group as a potential axial base), giving (P^Py)Fe^III-O₂^•- (2) (Li Y et al., Polyhedron 2013; 58: 60–64), we report here on (i) its use in forming a cytochrome c oxidase (CcO) model compound, or (ii) in a reaction with nitrogen monoxide (•NO; nitric oxide) to mimic nitric oxide dioxygenase (NOD) chemistry. Reaction of (2) with the cuprous chelate [Cu^I(AN)][B(C₆F₅)₄] (AN = bis[3-(dimethylamino)propyl]amine) gives a meta-stable product (3a), possessing a high-spin iron(III) and Cu(II) side-on bridged peroxo moiety with a μ-η²:η²-binding motif. This complex thermally decays to a corresponding μ-oxo complex [(P^Py)Fe^III-(O^2-)-Cu^II(AN)][B(C₆F₅)₄] (3). Both (3) and (3a) have been characterized by UV-vis, ²H NMR and EPR spectroscopies. When (2) is exposed to •NO_(g), a ferric heme nitrato compound forms; if 2,4-di-tert-butylphenol is added prior to •NO_(g) exposure, phenol ortho-nitration occurs with the iron product being the ferric hydroxide complex (P^Py)Fe^III(OH) (5). The latter reactions mimic the action of NOD's.

Novel tin(IV) halo complexes of an N-confused tetraphenylporphyrin with different axial ligands have been synthesized and characterized by various spectroscopic methods including X-ray crystallographic analysis. The molecular structures of the dichloro and dibromo derivatives possess perfect octahedral geometries, which are nearly comparable to the corresponding regular porphyrin complexes. In contrast, the iodide/triiodide complex obtained by a same reaction manner, demonstrated that the tin(IV) cation is slightly displaced towards axially coordinated iodide anion, giving rise to the different electronic structure due to the tautomeric form of N-confused porphyrin ligand. These structural differences reflected to the distinct photophysical and electrochemical properties. The Sn(IV) complexes are near IR luminescent, however the unsymmetrical axial coordination of iodide and triiodide anions in the tin(IV) N-confused porphyrin complex allows, in particular, the longer emission lifetimes and a smaller singlet-triplet energy gap, which were investigated by steady-state and time-resolved spectroscopies as well as theoretical calculations.

Cobalt(II) phthalocyanine has been encapsulated into the supercage of X-type zeolite as an active monomer (CoPc-X) by the "ship-in-bottle" synthesis method, and furthermore the CoPc-X has been ion-exchanged with secondary metals (Mⁿ⁺ = Na⁺, Ag⁺, Cu²⁺, Zn²⁺) to obtain CoPc-Mⁿ⁺-X. They have been characterized by elemental analysis, fluorescent X-ray, UV-vis, diffuse reflectance, physisorption analysis, and ESR spectroscopic methods, and their deodorant behaviors for smell gasses, 2-nonenal and indole, have been examined.

A new type of nickel and palladium complexes with non-innocent β-diketiminate ligand having redox active phenol groups, 2,4-di-tert-butyl-6-(((1E,2E)-3-((3,5-di-tert-butyl-2-hydroxyphenyl)amino)-2-nitroallylidene)amino)phenol (LH₃, fully protonated form) have been developed, and the structure, physical properties, and reactivity of their one-electron and two-electron oxidized complexes, [M^II(L^•2-)] and [M^II(L^-)]⁺ (M = Ni^II or Pd^II) have been examined in detail. The two-electron oxidized forms of both complexes, [M^II(L^-)]⁺, exhibited hydrogen atom abstraction ability from 1,4-cyclohexadiene (CHD) comparable to its copper analog [Cu^II(L^-)]⁺ (Dalton Trans. 2013; 42: 2438-2444). The one-electron oxidized form of palladium complex, [Pd^II(L^•2-)], was also found to oxidize CHD, whereas the nickel analog, [Ni^II(L^•2-)], exhibited photo-induced oxidation ability of CHD.

Bis-porphyrins containing a β,β′-fused pyrazino (Pz) linking group were examined by electrochemistry and thin-layer UV-visible spectroelectrochemistry in PhCN containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) as supporting electrolyte. The investigated compounds are represented as M(TPP)-Pz-(TPP)M, where TPP is the dianion of tetraphenylporphyrin and M = Zn(II), Cu(II) or Ag(II). The effect of the linking Pz group on the redox potentials and UV-visible spectra of the neutral, electroreduced and electrooxidized bis-porphyrins is discussed and the data compared to what is observed for related monoporphyrins and earlier characterized bis-porphyrins containing a tetraazaanthracene (TA) linking group and the same central metal ions. The Cu(II) and Zn(II) Pz linked bis-porphyrins exhibit a relatively strong interaction between the two equivalent porphyrin macrocycles as evidenced by UV-visible spectra of the neutral compounds and characteristic splitting of redox processes for three of the four electron transfer reactions, the one exception being the first oxidation, where no splitting of potentials is observed in the formation of the bisporphyrin bis-cation radical, [M(TPP)-Pz-(TPP)M]²⁺. The first oxidation and first reduction of the bis-porphyrin with two Ag(II) central metal ions occurs via two overlapping one-electron transfer steps in each process indicating equivalent, but non-interacting redox centers. This difference in redox behavior is due to differences in the site of electron transfer, metal centered for the Ag(II) bisporphyrins, which undergo Ag(II)/Ag(III) and Ag(II)/Ag(I) processes as compared to only ring centered electron transfers for the Cu(II) and Zn(II) derivatives. The Pz-linked Zn(II) bis-porphyrins have a larger average HOMO–LUMO gap (2.01 V) as compared to related tetraazaanthracene linked bis-porphyrins (1.67 V), which were earlier characterized in the literature, but the gap is smaller than that for the mono-porphyrins with the same central metal ions (2.17 V). Each redox reaction of the investigated bisporphyrins was characterized by thin-layer spectroelectrochemistry.

Gold(III) compounds continue to be explored for their potential utility as anticancer agents. A recognized limitation is the reactivity of gold(III), which is typically reduced to the more labile gold(I) state under physiological conditions. The use of porphyrins can overcome this problem. However, to date the stabilization provided by the use a strongly chelating porphyrin is offset by the poor solubility of the resulting complex in aqueous media. In this work, we describe the synthesis and in vitro anti-cancer activity of a gold(III)porphyrin complex with relatively good aqueous solubility. As judged from standard antiproliferation assays, this complex displays an IC₅₀ of 9 μM for the A2780 human ovarian cancer cell line. This is a higher level of potency than displayed by two related control systems.

The synthesis and structural characterization and the study of the electronic properties of two novel porphyrin-bridge-fullerene molecules, where a free-based porphyrin and [60]fullerene are connected through one and two units of ethylenedioxythienylenevinylene π-conjugated bridges, is reported. The absorption studies, voltamperometric measurements and theoretical calculations at DFT level are presented. A HOMO–LUMO gap as low as 1.41 eV has been found for compound 6.

We found that oxidation of cyclic ethers with the Ru porphyrin-heteroaromatic N-oxide system gave lactones or/and ring-opened oxidized products with regioselectivity. A relatively high kinetic isotope effect was observed in the ether oxidation, suggesting that the rate-determining step is the first hydrogen abstraction.

The catalytic conversion of methanol to formaldehyde by three kinds of non-porphyrin Ru complexes, Ru^IVO(TPA) (TPA = tris(2-pyridylmethyl)amine) (1a), Ru^IVO(6-COO-TPA) (6-COO-TPA = 2-(6-carboxyl-pyridyl)methyl-bis(2-pyridylmethyl)amine) (1b), and Ru^IVO(N4Py) (N4Py = N,N-bis(2-pyridyl-methyl)-N-bis(2-pyridyl)methylamine) (1c), is discussed by using density functional theory (DFT) calculations. There are two possible reaction pathways for the oxidation of methanol to formaldehyde with respect to the first hydrogen abstraction from the methyl group (path 1) and the hydroxyl group (path 2). Path 1 and path 2 involve the hydroxymethyl radical (•CH₂OH) and the methoxyl radical (CH₃O•), respectively, as an intermediate. DFT calculations demonstrate that the two pathways are energetically comparable in the reactions by the three Ru^IV–oxo complexes. The reactions with 1a and 1c are initiated by the C–H bond dissociation with activation barriers of 22.2 and 21.4 kcal/mol, respectively, while the reaction with 1b is initiated by the O–H bond dissociation with an activation barrier of 18.1 kcal/mol. However, the calculations showed that the rate-determining step is the H-atom abstraction from the CH₃ group of methanol in all the pathways. These results are in good agreement with kinetic analysis of the reactions by the Ru^IV–oxo complexes, being useful for considering the mechanism of methanol oxidation.

A trichromophoric dyad composed of an octa-β-alkyl-palladium(II)porphyrin (donor) and two tri-meso-aryl-zinc(II)porphyrins (acceptors) held by a truxene spacer exhibits very fast rates for triplet energy transfers at 77 (k_ET(T₁) = 1.63 × 10⁸ s^-1) and 298 K (k_ET(T₁) = 3.44 × 10⁸ s^-1), whereas the corresponding singlet energy transfer rates, k_ET(S₁) = 3.9 × 10¹⁰ s^-1 (77 K) and k_ET(S₁) = 6.0 × 10¹⁰ s^-1 (298 K), are also considered fast. The interpretation for these results is that the energy transfer processes proceed via a through bond Dexter mechanism (i.e. double electron exchange) supported by comparison with literature data and evidence for a moderate MO coupling between the donor and acceptor chromophores in the frontier MOs.

A diruthenium complex with a free-base porphyrin linker 1 is synthesized and characterized by ¹H and ³¹P NMR, IR, and ESI-TOF-MS spectroscopy. A cyclic voltammogram of 1 shows two reversible waves attributed to the redox processes at the ruthenium centers, and a compropotionation constant (K_C) has been determined to be 1.8 × 10⁵, indicating that a mixed valence state of 1⁺ is thermodynamically stable. The monocationic complex 1⁺ obtained by chemical oxidation of 1 by [Cp₂Fe]PF₆ shows an intervalence charge transfer (IVCT) band in the NIR region. On the basis of the electronic coupling (V_ab) of 2644 cm^-1 obtained by analysis of the IVCT band, complex 1^+• is assigned as a Class III compound according to the Robin–Day classification. DFT calculation and IR study suggest that the strength of π-back donation is one of key determinants for a strong electronic coupling between the two metal centers.

We synthesized a diporphyrin compound [4,7-bis[5-[arylethynyl]-10,20-bis{(triisopropylsilyl)ethynyl}porphyrin-15-yl]]-2,1,3-benzothiadiazole dimagnesium(II)], in which two porphyrin units were linked using a benzodiathiazole unit as an electron-withdrawing moiety. These diporphyrins have low-lying HOMO and LUMO levels with long-wavelength light absorption property. Power conversion efficiency of the organic solar cell using this diporphyrin and mix-PCBM (a 85:15 mixture of [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) and [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) was 2.75% with short-circuit current density of 8.79 mA/cm², open-circuit voltage of 0.80 V, and fill factor of 0.39. Photocurrent conversion in the near infrared region was demonstrated by the incident photon-to-current efficiency spectrum.

The new visible-light operated CO₂-glucose biofuel cell consisting of chlorin-e₆ immobilized on TiO₂ thin layer film onto optical transparent conductive glass electrode (OTE) as an anode, formate dehydrogenase (FDH) and viologen with long alkyl chain co-immobilized OTE as a cathode, and the solution containing glucose, glucose dehydrogenase (GDH) and NAD⁺ as a fuel was developed. The short-circuit photocurrent and the open-circuit photovoltage of this cell are 37 μA.cm^-2 and 390 mV, respectively. The maximum power is estimated to be 57 μW.cm^-2. The overall photoenergy conversion efficiency is estimated to be 0.057%. After 2 h irradiation to this cell, 0.65 μmol of formic acid was produced. During irradiation, the photocurrent was constant value of 32 ± 10 μA.cm^-2 in the cell. Thus, CO₂ reduces and formic acid produces while generating electricity with visible light irradiation to this biofuel cell.

The copper(II), nickel(II), etc. complexes of 5,15-bis(trimethylsilylethynyl)tetrabenzoporphyrin (TMS-H₂BP) and 5,15-bis(triisopropylsilylethynyl)tetrabenzoporphyrin (TIPS-H₂BP) have been prepared from the corresponding bicycle[2.2.2]octadiene(BCOD)-fused precursors by the retro-Diels–Alder reaction. X-ray diffraction (XRD) analyses show that TMS-H₂BP and its metal complexes of zinc(II) (TMS-ZnBP) and copper(II) (TMS-CuBP) adopt flat molecular conformations and form herringbone-type packing structures in the single crystalline state. TIPS-H₂BP and the zinc(II) and copper(II) complexes (TIPS-ZnBP and TIPS-CuBP) are similar to the TMS derivatives in molecular conformation, but these TIPS derivatives form one-dimensional slipped-stack structures. The nickel complexes TMS-NiBP and TIPS-NiBP have U-shaped structures because of the small size of nickel(II) ion. Solution processed organic thin-film transistors of the benzoporphyrins were fabricated and TMS-H₂BP showed the highest hole mobility of 0.11 cm².V^-1.s^-1. Bulk heterojunction organic solar cells based on TMS- or TIPS-H₂BP and their metal complexes as p-type and PC₇₁BM as n-type materials were fabricated by solution process. Atomic force microscopy and thin-film XRD measurements indicated that the film crystallinities were increased by raising the annealing temperature over 180°C or by changing the substituents from triisopropylsilyl to trimethylsilyl. The best power-conversion efficiency (PCE) of 1.49% was achieved with TMS-ZnBP by annealing at 180°C with a moderate crystallinity and smooth surface.

Two rarely seen building blocks have been incorporated into light absorbing arrays: corroles and 2,3-naphthalimides. General synthetic strategy consisting in direct condensation of formyl substituted aromatic imides with dipyrranes led to diverse range of trans-A₂B-corroles in acceptable yields. Spectroscopic properties of all five dyads studied suggest that regardless the imide's structure, components are weakly electronically coupled. Positioning 2,3-naphthalimide unit partially above the corrole core leads to slight alteration of their optical properties. Dyads bearing blue-absorbing imide components display different behavior depending on their structure. In corrole linked with naphthalenyl-naphthalene-1,8-carboximide a 100% effective energy transfer reaction from the imide component to the corrole component occurred. On the contrary, in small, strongly polarized amino-cyano-phthalimide neither efficient energy-nor electron-transfer could be detected and excitation leads to fluorescence from both components.

A water-soluble manganese porphyrin complex was examined for the catalytic formation of chlorine dioxide from chlorite under ambient temperature at pH 5.00 and 6.90. Quantitative kinetic modeling allowed for the deduction of a mechanism that accounts for all experimental observations. Catalysis is initiated via an OAT (Oxygen Atom Transfer) reaction resulting in formation of a putative manganese(V) oxo species, which undergoes ET (Electron Transfer) with chlorite to form chlorine dioxide. As chlorine dioxide accumulates in solution, chlorite consumption slows down and ClO₂ reaches a maximum as the system reaches equilibrium. In phosphate buffer at pH 6.90, manganese(IV) oxo accumulates and its reaction with ClO₂ gives ClO₃^-. However, at pH 5.00 acetate buffer proton coupled electron transfer (PCET) from chlorite to manganese(IV) oxo is fast and irreversible leading to chlorate formation only via the putative manganese(V) oxo species. These differences underscore how PCET rates affect reaction pathways and mechanism. The ClO₂ product can be collected from the aqueous reaction mixture via purging with an inert gas, allowing for the preparation of chlorine dioxide on-demand.

Phosphorus complexes of non-planar α-octaaryl phthalocyanine derivatives ((α-Ar)₈Pc), 3a and 3b have been synthesized by introduction of phosphorus(V) ions into free-base Pcs 2a and 2b. 3a and 3b were characterized by MS, ¹H and ³¹P NMR spectra. The solid state structure of 3a indicated a ruffled Pc structure due to the small atomic radius of phosphorus, although the corresponding free-base Pc 2a has a saddled Pc structure. The phosphorus complexes showed intense absorption bands (Q-bands) in the near-IR region, while the introduction of electron-donating groups at the peripheral phenyl groups was efficient for additional red-shifting of the Q-band. Electrochemical data revealed that the red-shift of the Q-band is attributable to a decrease in the HOMO–LUMO gap due to significant and moderate stabilization of the LUMO and HOMO, respectively. MO calculations suggested that the phosphorus(V) ion intensified the electronic interaction between the peripheral aryl moieties and the Pc macrocyclic core.

A non-precious metal catalyst (NPMC) promoting a four-electron oxygen reduction reaction (ORR) was synthesized by heat treatment of myoglobin (Mb) containing a heme (iron protoporphyrin IX) as a source of iron, nitrogen, and carbon atoms. Samples of the mixture of Mb and carbon black (Vulcan XC72R: VC) were pyrolyzed at 740, 840, 940, 1040 or 1140°C under N₂ flow. The microstructures of the carbonized Mb catalysts were characterized by XRD, Raman spectroscopy, XPS, and TEM. Results indicate that the iron-containing active site is embedded within the surface structure in an amorphous domain of the carbon materials. The catalyst ink in a 0.05 wt% Nafion solution in isopropanol was coated onto a glassy carbon electrode and the ORR activity of Mb-based NPMCs was evaluated in a rotating disk electrode experiment in an O₂-saturated 0.1 M HClO₄ solution at 25°C. The catalyst synthesized at 940°C has the highest ORR activity in terms of the onset potential and the current density. In contrast, pyrolytic temperatures above 940°C decrease the activity, suggesting that the active structure of the catalyst apparently decomposes at higher temperatures. The Koutecky–Levich plots indicate that the Mb-based catalyst prepared at 940°C catalyzes four-electron ORR (n = ca. 4). The catalysts prepared at other temperatures have n values of 3.6 at 740°C, 3.7 at 840°C, and 2.9 at 1040°C. The ORR of Mb/VC is diffusion-controlled at potentials lower than 0.3 V (vs. RHE) and the onset potential is 0.84 ± 0.01 V.

A series of chlorophyll derivatives possessing a carboxy group were synthesized aiming at their application as sensing materials and to dye-sensitized solar cells (DSSCs). Their absorption and fluorescence responses to amine concentrations in THF and photovoltaic performance of DSSCs on TiO₂ films were investigated.

Polarized electroabsorption (E-A) spectra of highly efficient porphyrin sensitizers (YD2 and YD2-oC8) have been measured in benzene solution. Polarized E-A spectra of these push–pull porphyrins embedded in poly(methyl methacrylate) films or sensitized on TiO₂ films are also observed. Based on the analysis of the E-A spectra, the magnitude of the electric dipole moment both in the ground state and in the lowest excited state have been evaluated in solution and in solid films. The electric dipole moment in the excited state of these compounds is very large on TiO₂ films, suggesting the interfacial charge transfer on TiO₂ surface following photoexcitation of porphyrin dyes. The electric dipole moment in the excited state evaluated from the E-A spectra is very different from the one evaluated from the electrophotoluminescence spectra on TiO₂, suggesting that the strong local field of TiO₂ films is applied to the fluorescing dyes attached to TiO₂ films.

We report herein the synthesis of a dinucleotide bearing pendant porphyrins dedicated to adopt a pre-organized coformation with face-to-face porphyrins, and capable to self-organize in a stable sandwich type complexe with bidentate base such as DABCO. Earlier studies demonstrated that a peptidic linker does not provide sufficient pre-organization to enhance significantly the association constant with bidentate bases such as DABCO on the contrary of some other flexible linkers such as uridine or 2′-deoxyuridine. We document herein that the gain in stability for the formation of sandwich type host–guest complex with DABCO can be even greater when a dinucleotide linker is used. Such pre-organization increases the association constants by one to two orders of magnitude when compared to the association constants of the same bidentate ligands with a reference Zn(II) porphyrin. Comparison of these results with those obtained for rigid tweezers shows a better efficiency of the flexible nucleosidic dimers. We thus document the fact that the choice of rigid spacers is not the only way to pre-organize bis-porphyrins, and that some well-chosen nucleosidic linkers offer an interesting option for the synthesis of such devices. Furthermore, the chirality and enantio-purity of the nucleosidic linkers paves the way toward the selective complexation of enantio-pure bidentate guests and the resolution of racemates.