Phthalocyanine Units Research Articles

Tandem Cofacial Stacks of Porphyrin–Phthalocyanine Dyads through Complementary Coordination

A novel straightforward methodology to organize discrete heterogeneous stacks of porphyrin and phthalocyanine employed an imidazolyl-to-zinc complementary coordination protocol for a Zn(II) phthalocyanine that contains an imidazolyl terminal with an ethynylporphyrin as a coplanar spacer. Structural elucidation was performed by means of size-exclusion chromatography, spectral titration, and NMR spectroscopy. The association constants for the complementary coordination of the heterogeneous slipped-cofacial tetrads reached extremely high values, in the order of 10(14) M(-1). Close contact of the porphyrin and phthalocyanine planes led to a strong shielding of the cofacial protons, which were split due to the slipped-cofacial heterogeneous environment. In variable-temperature NMR spectroscopy, the split signals remained in the aromatic region, a result suggesting structural robustness. Addition of trifluoroacetic acid dissociated the coordination structure to unify the split signals. The stacked tetrads showed unique electronic structures, such as strong exciton coupling and charge-transfer properties between the porphyrin and phthalocyanine units, which were modulated by the peripheral substituents of the phthalocyanine subunit and by the solvent. Interconversion between the coordination tetrad and the corresponding dyad was observed upon addition of an axial ligand.

Dinuclear and Tetranuclear Copper(II) Complexes with a Ligand Bearing Phthalocyanine and Schiff-Base Coordination Sites

Abstract Dinuclear and tetranuclear copper(II) complexes with a ligand bearing phthalocyanine and Schiff-base coordination sites were prepared and characterized. The dinuclear complex has two copper(II) phthalocyanine units linked by 2,6-diiminomethyl-4-methylphenol. The imino nitrogen (Schiff-base) coordinates to two more copper(II) ions to give a tetranuclear copper(II) complex composed of a hydroxo- and phenoxo-bridged copper(II) dinuclear unit and two copper(II) phthalocyanine units. Magnetic, spectroscopic, and electrochemical studies showed that there is no significant interaction among the two copper(II) phthalocyanine units and the hydroxo- and phenoxo-bridged dinuclear unit.

Synthesis, Characterization, and Electrochemical and Electrical Properties of Novel Pentaerythritol‐Bridged Cofacial Bismetallophthalocyanines and Their Water‐Soluble Derivatives

AbstractNovel cofacial bismetallophthalocyanines and theirwater‐soluble derivatives were prepared. The precursor4,4′‐(2‐phenyl‐1,3‐dioxane‐5,5‐diyl)bis(methylene)bis(oxy)diphthalonitrile 3 was obtained by the reaction of [5‐(hydroxymethyl)‐2‐phenyl‐1,3‐dioxan‐5‐yl] methanol 1 and 4‐nitrophthalonitrile 2 with K2CO3 in DMF at 50 °C. Cyclotetramerization was achieved by heating the homogenized mixture of the precursor, bisphthalonitrile, and Zn(OAc)2·2H2O or Co(OAc)2·4H2O at 300 °C, which was followed by catalytic hydrogenation of the resulting product with Pd/C(10 %) in DMF. The target water‐soluble phthalocyanines were acquired from boiling suspensions of the compounds bearing eight OH side groups in aqueous KOH (20 %) solution. The structure of the target compounds was confirmed by elemental analysis, FTIR, UV/Vis, 1H NMR, ICP‐MS, and MALDI‐TOF spectroscopic methods. The electrochemical and spectroelectrochemical measurements suggested the formation of various mixed‐valent oxidation and reduction species, as a result of the strong intramolecular interactions between the two cofacial phthalocyanine units in the compounds. Impedance spectroscopy, dc conductivity, and thermopower measurements were performed using spin‐coated films of these compounds as a function of temperature (290–440 K) and frequency (40–105 Hz). Dc conductivity showed typical Arrhenius behavior for all compounds. At low temperatures, a curved line was observed for the complex plane plots of impedance for all phthalocyanines. These curved lines transformed into a full semicircle with increasing temperature. The dependency of frequency exponent s on temperature suggested hopping‐type conduction. A positive Seebeck coefficient was observed for all compounds, which indicates that the compounds behave as a p‐type semiconductor. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Synthesis, characterization, and electrochemical and electrical properties of novel mononuclear and binuclear ball-type Zn(II) and Co(II) phthalocyanines substituted with 1a,8b-dihydronaphtho[ b]naphthofuro-[3,2- d]furan-7,10-diyl

New mononuclear phthalocyanines [Zn(II) 4 and Co(II) 6] and ball-type bisphthalocyanines [Zn(II) 5 and Co(II) 7] have been synthesized from the corresponding compound 3, which can be obtained from the reaction of 4-nitrophthalonitrile 1 with 1a,8b-dihydronaphtho[ b]naphthofuro[3,2- d]furan-7,10-diol 2. The novel compounds have been characterized by elemental analysis, UV/Vis, IR, 1H NMR and MASS spectroscopy. The electrochemical measurements show the formation of various mixed-valence oxidized and reduced species, due to intramolecular interactions between the two phthalocyanine units in the ball-type binuclear metallophthalocyanines. Detailed studies of the effect of temperature on the electronic properties of the films were investigated by dc conductivity and impedance spectroscopy techniques at temperatures between 290 K and 460 K. Thermally activated conductivity dependence on temperature was observed from the dc measurements. The ac results give a power law behavior in which the frequency exponent decreases with temperature. It was observed that the impedance spectra consist of a curved line at low temperature. These curved lines transform into a full semicircle with increasing temperature.

Phthalocyanine Conductors: New Trend for Crystal and Functionality Design

Conductors obtained from axially substituted phthalocyanine units are presented. In contrast to face-to-face one-dimensional stacking in conductors with planar phthalocyanins, various types of π–π stacking structures can be obtained owing to the slipped stacking.

Control Over Charge Separation in Phthalocyanine−Anthraquinone Conjugates as a Function of the Aggregation Status

We have prepared three isomeric donor-acceptor systems, in which two phthalocyanine (Pc) units have been attached to the 1-,5- (1a), 1-,8- (1b), or 2-,6- (1c) positions of a central anthraquinone (AQ) moiety, leading to packed (1b) or extended (1a and 1c) topologies. The electronic interactions between the donor and the acceptor in the ground state or in the excited states have been studied by different electrochemical and photophysical techniques. Due to the markedly different topologies, we have been able to modify these interactions at the intramolecular level and, by a proper choice of the solvent environment, at the intermolecular level within aggregates. In triad 1b, the ZnPc units are forced to pi-stack cofacially and out of the plane of the AQ ring. Consequently, this molecule shows strong inter-Pc interactions that give rise to intramolecular excitonic coupling but a relatively small electronic communication with the AQ acceptor through the vinyl spacers. On the contrary, the 1-,5- or 2-,6-connections of triads 1a and 1c allow for an efficient pi-conjugation between the active units that extends over the entire planar system. These two molecules tend to aggregate in aromatic solvents by pi-pi stacking, giving rise to J-type oligomers. Photoexcitation of the Pc units of 1a-c results in the formation of the Pc.+-AQ.- charge transfer state. We have demonstrated that the kinetics of these electron transfer reactions is greatly dependent on the aggregation status of the triads.

New Donor–Acceptor Materials Based on Random Polynorbornenes Bearing Pendant Phthalocyanine and Fullerene Units

New donor-acceptor materials based on a polynorbornene framework to which both phthalocyanine and C60 electroactive pendant units are randomly attached have been prepared in good yield by ring-opening-metathesis polymerization (ROMP) in the presence of a Grubbs catalyst. A structurally related phthalocyanine homopolymer was also synthesized for comparison. A remarkable fluorescence quenching was observed in the homopolymer and accounts for PcPc interactions along the polymeric framework. As expected, the fluorescence quenching increases in the case of the polynorbornenes containing both Pc and C60 units owing to photoinduced electron transfer, which was further confirmed by transient absorption spectroscopy. Finally, preliminary solar cell devices made of one of the copolymers were constructed.

Synthesis and Photophysical Properties of Annulated Dinuclear and Trinuclear Phthalocyanines

Metal-free mononuclear, dinuclear and trinuclear phthalocyanines were prepared by a mixed cyclotetramerisation of a 1,2,4,5-tetracyanobenzene derivative and 4,5-bis(2,6-dimethylphenoxy)phthalonitrile. For the first time, a pi-electron-conjugated trinuclear phthalocyanine was synthesised with phthalocyanine units connected by common annulated benzene rings. The Q band of the trinuclear compound in solution occurs at lambda = 944 nm whereas those of the dinuclear and mononuclear compounds are at lambda = 853/830 and 701/664 nm, respectively. Fluorescence quantum yields, fluorescence lifetimes and singlet-oxygen quantum yields of the compounds were determined.

Unusual mesomorphic behaviour of an ethynyl-substituted phthalocyanine

An ethynyl-substituted nickel(II) phthalocyanine has been synthesised and its thermotropic properties studied; optical microscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques revealed an unusual mesomorphic behaviour observed for the first time in phthalocyanine systems where each disk of the hexagonal columnar mesophase is formed by two ethynyl-substituted phthalocyanine units.

Thermal and Electrical Behavior of Fe(III)‐2,9,16,23‐Tetracarboxyamidephthalocyanine‐Grafted Poly(Ethylene‐Co‐Vinylacetate)

Poly(ethylene‐co‐vinylacetate) (EVA) was subjected to a displacement reaction in order to replace acetyl groups by a light‐sensitive organometalic complex, Fe(III)‐2,9,16,23‐tetracarboxyamide‐phthalocyanine [Fe(III)‐taPc]. The new grafted EVA copolymer contains Fe(III) ions taking part in a complex structure; it presents the characteristics of a reversible cross‐linked structure that acts as a thermoplastic when heated at temperatures higher than 150°C. The Simultaneous Thermal Analyzer technique (STA), which involves both Thermogravimetry (TG) and Differential Thermal Analysis (DTA) techniques, was able to detect grafted phthalocyanine units by their characteristic degradation around 680–700°C where it exhibits a broad, sharp endotherm. The grafted copolymer films electrical conductivity response was studied by applying different electric fields and temperatures. The polarization charge and electronic charge conductivity contribute to the whole conductivity below the glass transition temperature. By measurements of current density it is able to detect the samples glass transition.

Synthetic N‐Substituted Metal Aza‐macrocyclic Complexes: Properties and Applications

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthetic N-substituted metal aza-macrocyclic complexes: properties and applications

Recent contributions to the chemistry of macrocyclic metal complexes and ligands are reviewed. The compounds reviewed have the following structural features: aza-macrocycles having 1,10-phenanthroline and 2,2′-bipyridine groups and pendants arms; highly aromatic aza-macrocycles with phthalocyanine and porphyrin units incorporating pendant arms; aliphatic aza-macrocycles with pendant arms and/or polynucleating aza-macrocycles. Several of their chemical properties are critically reviewed but the emphasis is on structural and synthetic details.

Inducing solid-state isolation of the phthalocyanine macrocycle by its incorporation within rigid, randomly shaped oligomers

The synthesis and properties of two non-planar and highly rigid pentamers containing four phthalocyanine units linked, via a spirocyclic fused ring system, to a central phthalocyanine or porphyrin core is described. It is shown that the rigidity of these novel oligomers, together with the large number of structural isomers of irregular shape induced by the presence of the four spiro-centres, inhibits efficient packing of the macrocycles in the solid state. Therefore, the UV–visible absorption spectrum of spin-coated films of these materials is almost identical to that obtained from the non-aggregated oligomers in dilute solution. Nitrogen adsorption measurements indicate a high surface area for one of the pentamers, which is consistent with some degree of microporosity.

Brewster angle microscopy and surface potential measurements of Langmuir–Blodgett films of zinc tri( tert-butyl)-4-sulphophthalocyanine

The formation of a Langmuir monolayer of an amphiphilic derivative of zinc phthalocyanine (Na[ZnPc tSO 3]) has been studied by means of surface potential technique and Brewster angle microscopy. The experiments were undertaken in order to understand the behaviour of this monolayer with a well-defined surface pressure isotherm. The floating film is described as a truly monomolecular layer formed by very rigid islands in which the phthalocyanine units tend to take on a preferential orientation with their planes perpendicular to the air–water interface, for high values of the surface pressure.

Synthesis and Magnetic Properties of a Planar Binuclear Copper(II) Phthalocyanine Complex

Abstract A binuclear copper(II) phthalocyanine complex, in which two Cu(II) phthalocyanine units are linked by their common benzene ring to give a planar structure, was prepared and investigated concerning its magnetic properties. No significant magnetic interaction was found between the copper(II) ions through the benzene ring.

Synthesis and Excited State Dynamics of μ-Oxo Group IV Metal Phthalocyanine Oligomers: Trimers and Tetramers

Two μ-oxo silicon phthalocyanines have been synthesized and subjected to photophysical examination. The results have been compared to the monomeric and dimeric systems published previously. The Q-bands in the ground state absorption spectra undergo a blue shift with respect to the monomer due to an excitonic interaction of the transition dipoles of the coplanar silicon phthalocyanine units having central symmetry along the Si−O−Si axis, with no significant molecular orbital overlap. This excitonic interaction generates a new set of excited states. The Q-band shift (with respect to the monomer) is greater as the number of phthalocyanine rings is increased consistent with the molecular exciton model of a linear polymer. On suprananosecond time scales, photoexcitation generated optical absorptions of triplet states that decayed with intrinsic lifetimes in the tens of microseconds region. These were quenched in the presence of O2 with bimolecular rate constants for the trimer and tetramer of near 2 × 106 M-1 s-1, indicating that the T1 states of the trimer and tetramer lie significantly below the energy of the 1Δg state of oxygen (22.5 kcal mol-1). Estimates of the energy of T1 generated values of approximately 17 kcal mol-1 for both compounds, some 2 kcal mol-1 lower than that calculated for the dimer. Photon absorption results in the formation of the highest lying exciton state, which deactivates to the lowest exciton state, which subsequently undergoes intersystem crossing to the triplet manifold. The ultrafast pump−probe results demonstrated that part of the lowest exciton state population was complete within the instrument rise time, whereas other populations required several picoseconds to develop, probably on account of the requirement for torsional/vibrational relaxation of excited state populations produced from ground state molecules having lower symmetry than D4h.

New polythiophenes bearing electron-acceptor phthalocyanine chromophores

Two new donor–acceptor copolymers comprising a polythiophene backbone, and bearing phthalocyanine chromophores on the side chains have been prepared. Preliminary photophysical characterization of these materials by FTIR photoinduced absorption indicates that electron transfer from the polythiophene to the phthalocyanine units takes place.

Donor-acceptor phthalocyanine nanoaggregates.

A novel donor-acceptor bisphthalocyanine (bis-Pc, 1) in which two different Pc units (Zn(II)-Pc and Ni(II)-Pc) are linked via vinylene spacers to the pseudopara positions of a central [2.2]paracyclophane moiety is described. The synthesis of 1 is achieved by two successive Heck reactions of pseudopara-divinyl[2.2]paracyclophane 9 with, sequentially, a zinc(II)- and a nickel(II)-iodophthalocyanine (4 and 5, respectively). The self-assembly ability of 1, which is the result of the complementary donor-acceptor character of its phthalocyanine units, has been assessed by a variety of techniques. It is revealed that 1 forms one-dimensional aggregates of nanometer-sized dimension, whereas equimolar mixtures of the donor and acceptor Pc subunits 2 and 3, although strongly interacting, do not give large arrays. The aggregates of 1 represent a novel type of supramolecular polymers based mainly upon donor-acceptor interactions.

"Stapled" bis(phthalocyaninato)niobium(IV), Pc2Nb: X-ray crystal structure, chemical and electrochemical behavior, and theoretical studies. Perspectives for the use of Pc2Nb (thin films) as an "optically passive electrode" in electrochromic devices.

Recrystallization of the previously reported monosolvated bis(phthalocyaninato)niobium(IV), [Pc2Nb].CINP (CINP = 1-chloronaphthalene), has allowed isolation of a single crystal of a new solvated form, i.e. [Pc2Nb]. 3.5CINP, whose structure has been elucidated by X-ray work: space group P2(1)/n (No. 14); a = 16.765(3), b = 23.800(4), c = 19.421(4) A; alpha = gamma = 90 degrees, beta = 92.51(2) degrees; Z = 4. The sandwiched material is a "stapled" molecule, characterized by the presence of two intramolecular interligand C-C sigma bonds and highly strained phthalocyanine units, as formerly observed by crystallographic work for its Ti(IV) analogue, [Pc2Ti], and the +1 corresponding fragment, [Pc2Nb]+, present in the species [Pc2Nb](l3)(l2)0.5.3.5CINP. [Pc2Nb] appears to be reluctant to undergo further oxidation above the +1 oxidation state. Detailed theoretical studies by DFT and TDDFT methods have been developed on [Pc2Nb] and [Pc2Nb]+, also extended for comparison to the Ti(IV) complex [Pc2Ti], and an adequate picture of the ground-state electronic structure of these species has been achieved. Moreover, the excitation energies and oscillator strengths calculated for the closed-shell systems, [Pc2Ti] and [Pc2Nb]+, provide a satisfactory interpretation of their characteristic visible optical spectra and help to rationalize the similar features observed in the visible spectrum of the open-shell "stapled" complex, [Pc2Nb]. Thin solid films (100-250 nm) of [Pc2Nb] deposited on ITO (indium-doped tin oxide) show a reversible redox process in neutral or acidic aqueous electrolytes. The electrochemical and electrochromic properties of the sandwiched complex, combined with impedance and UV/visible spectral measurements, are presented and discussed. The achieved electrochemical information, while substantially in keeping with the observed chemical redox behavior and theoretical predictions, qualifies [Pc2Nb] as an "optically passive" electrode and a promising material for its use in electrochromic devices.

Synthesis and electropolymerisation of pyrrol-1-yl substituted phthalocyanines

2,9,16,23-Tetrakis(2-pyrrol-1-ylalkoxy)phthalocyanines, in which the phthalocyanine is connected via an alkylene spacer to a pyrrole substituent, are prepared via three steps in good yields. For the first time monomers with groups for electropolymerisation electronically isolated from the phthalocyanine are described. Films of thickness up to 5 µm of these pyrrole substituted phthalocyanines were obtained by oxidative electropolymerisation under potentiodynamic conditions or at constant potential. UV/Vis spectra show the presence of phthalocyanine and polypyrrole structural units in the polymers. The charge–discharge behaviour is accompanied by a reversible electrochromic colour change. The polymer films exhibit specific electrical conductivities of ∼10−5 S cm−1.