Phthalocyanine Units Research Articles

The influence of correlation effects on the electronic structure of double-decker bis(phthalocyaninato)-Dy, Tb complexes

By using DFT+U approach, we investigated the influence of the electronic correlation in the 4f manifold of lanthanide atom upon the electronic structure of double-decker bis(phthalocyaninato)-Dy, Tb complexes. We monitored the density of states, electronic populations and charge density properties in the framework of Hubbard U and J values, highlighting the different electronic behaviour of the two phthalocyanine units. Our results show that important changes occurs at the level of electronic populations, while the density of states of nitrogen atoms display only small changes, restricted to a specific energy window. We also emphasized the mechanisms connecting these changes to the geometric structure of the complexes. Finally, the dependence between possible spin communication channels and the strength of correlation in double-decker -Dy and -Tb molecules was examined.

Bis(hafnium(IV) stapled phthalocyanine) derivative complex. Synthesis and structure

Thermal reaction of phthalonitrile with hafnium powder under iodine monobromide (IBr) yields a new type molecule: bis(hafnium(IV) stapled phthalocyanine) derivative complex. X-ray single crystal analysis shows that the complex molecule consists of two hafnium phthalocyanine units bridged by the unique internal ligand that stapled by two carbon–carbon [Formula: see text] bonds to both HfPc-units. The internal dianionic ligand consists of two fragments, each of them present the three fourth part of phthalocyaninate ring. Both fragments are linked together through the bridging 1,2-di[amine(imine)methyl]benzene. The X-ray conformation of the bis(hafnium(IV) stapled phthalocyanine) derivative complex cation is confirmed by DFT calculations. An absence of the Q-band in the UV-vis spectrum, the typical band for the fully delocalized [Formula: see text]-electron aromatic phthalocyaninato(2-) ring system, indicates on drastic modification of the chromophore in this Hf-phthalocyanine complex that was confirmed by TD DFT calculations.

Oxygen Reduction to Water by a Cofacial Dimer of Iron(III)-Porphyrin and Iron(III)-Phthalocyanine Linked through a Highly Flexible Fourfold Rotaxane.

A μ-oxo-dinuclear iron complex of a supramolecular porphyrin-phthalocyanine conjugate was synthesized and its catalytic electrochemical oxygen reduction properties were investigated. In the conjugate, porphyrin and phthalocyanine units were connected to form a cofacial dimeric structure through a flexible fourfold rotaxane linkage, which was advantageous for accommodating small substrates between the iron centers. The conjugate showed efficient catalytic properties, at more positive potentials than those of other reported dinuclear porphyrinoid iron complexes, to selectively afford water through a four-electron reduction process.

Phthalocyanine based metal containing porous carbon sheet

Highly-ordered fused-ring poly copper phthalocyanine (PCuPc) was prepared using copper octacyanophthalocyanine as a building block, and two-dimensional (2D) square superlattices were directly observed by the transmission electron microscopy. Remarkably, we have found a formation of polymer network that consists of a 2D porous PCuPc sheet in which the centers of phthalocyanine units are alternately occupied by Cu atom and vacancy. Using this “half-filling” PCuPc, it must be possible to create alternating arrangements for transition metal centers, and therefore control the magnetic properties of the 2D carbon sheets.

Two-dimensional artificial light-harvesting antennae with predesigned high-order structure and robust photosensitising activity.

Highly ordered discrete assemblies of chlorophylls that are found in natural light-harvesting antennae are key to photosynthesis, which converts light energy to chemical energy and is the principal producer of organic matter on Earth. Porphyrins and phthalocyanines, which are analogues of chlorophylls, exhibit a strong absorbance of visible and near-infrared light, respectively. A highly ordered porphyrin-co-phthalocyanine antennae would harvest photons over the entire solar spectrum for chemical transformation. However, such a robust antennae has not yet been synthesised. Herein, we report a strategy that merges covalent bonds and noncovalent forces to produce highly ordered two-dimensional porphyrin-co-phthalocyanine antennae. This methodology enables control over the stoichiometry and order of the porphyrin and phthalocyanine units; more importantly, this approach is compatible with various metalloporphyrin and metallophthalocyanine derivatives and thus may lead to the generation of a broad structural diversity of two-dimensional artificial antennae. These ordered porphyrin-co-phthalocyanine two-dimensional antennae exhibit unique optical properties and catalytic functions that are not available with single-component or non-structured materials. These 2D artificial antennae exhibit exceptional light-harvesting capacity over the entire solar spectrum as a result of a synergistic light-absorption effect. In addition, they exhibit outstanding photosensitising activities in using both visible and near-infrared photons for producing singlet oxygen.

Assembly of Multi-Phthalocyanines on a Porphyrin Template by Fourfold Rotaxane Formation.

A stacked assembly composed of a porphyrin and two phthalocyanines was prepared through fourfold rotaxane formation. Two phthalocyanine molecules, bearing four 24-crown-8 units, were assembled onto a porphyrin template incorporating four sidechains with two dialkylammonium ions each through pseudorotaxane formation between crown ether units and ammonium ions. The Staudinger phosphite reaction, as the stoppering reaction, resulted in the formation of the stacked heterotrimer composed of a porphyrin and two phthalocyanines connected through a fourfold rotaxane structure. UV/Vis spectroscopic and electrochemical studies of the heterotrimer indicated that there is a significant electronic interaction between the two phthalocyanine units due to the close stacking. The electrochemical oxidation process of the stacked heterotrimer was studied by cyclic voltammetry and spectroelectrochemistry. Electron paramagnetic resonance (EPR) spectroscopy of a dinuclear Cu(II) complex, in which two Cu(II) phthalocyanines were assembled on a metal-free porphyrin template, revealed that two Cu(II) phthalocyanines were located within the stacking distance, which resulted in an antiferromagnetic interaction between the two S=1/2 spins in the ground state of the Cu(2+) ions in the heterotrimer.

Porous Azo-Bridged Porphyrin-Phthalocyanine Network with High Iodine Capture Capability.

We report a highly efficient iodine adsorbent achieved by rational design of a porous azo-bridged porphyrin-phthalocyanine network (AzoPPN), which was synthesized by a catalyst-free coupling reaction between free-base 5,10,15,20-tetrakis(4-nitrophenyl)-porphyrin and nickel tetraaminophthlocyanine. AzoPPN has a permanent porous structure and plenty of porphyrin and phthalocyanine units in the skeleton as effective sorption sites. It displays excellent adsorption of iodine vapor up to 290 wt. % and also shows remarkable capability as adsorbent for iodine in solution. This strategy of combining physisorption with chemisorption in one adsorbent will pave the way for the development of new materials for iodine capture.

First-Principles Study of Thermoelectric Properties of Covalent Organic Frameworks

Covalent organic frameworks (COFs) are new emerging functional porous materials. Strong covalent bonds result in molecular building blocks that can be arranged in layered two-dimensional (2D) or three-dimensional (3D) periodic networks. However, to the best of our knowledge, there have been no reports on experimental and theoretical studies of thermoelectrical properties of COFs to date. Therefore, density functional theory (DFT) and the Boltzmann transport equation have been applied in this work to calculate the semiclassical transport coefficients for phthalocyanine (Pc)-based NiPc, NiPc-benzothiadiazole (BTDA), and Pc COFs. Owing to the well-ordered stacking of the phthalocyanine units and linkers in these compounds, charge-carrier transport is facilitated in the stacking direction. In all studied compounds, the highly directional character of π-orbitals provides band-structure engineering and produces a type of low-dimensional hole transport along the stacking direction. All studied compounds are indirect semiconductors. The low-dimensional transport of holes and the localized states in both valence and conduction bands prevent the electron–hole compensation effect in the Seebeck coefficients, correlating with the large Seebeck coefficients of the studied compounds. Insertion of the electron-deficient building block benzothiadiazole in the NiPc-BTDA COF leads to positive Seebeck coefficients along the a-, b-, and c-directions. The relaxation time was estimated in our investigations from DFT band-structure calculations and the experimentally defined mobility, leading to determination of the electrical conductivity and electronic contribution to the thermal conductivity, as well as figure of merit (ZT) estimation. Ni atom provided greater electrical conductivity along the c-direction in comparison with metal-free Pc COF, and NiPc COF showed the highest thermoelectric performance among the studied COFs.

An acid-cleavable phthalocyanine tetramer as an activatable photosensitiser for photodynamic therapy.

An acetal-linked self-quenched zinc(ii) phthalocyanine tetramer has been prepared. In an acidic environment in phosphate buffered saline or inside tumour cells, the phthalocyanine units of the tetramer are separated thereby restoring the fluorescence emission and singlet oxygen production. This response enables this compound to serve as a promising activatable photosensitiser for photodynamic therapy.

Synthesis and Electric Modulus Formalism of Novel Metal-Phthalocyanine Bridged Polymers

Novel nickel and copper phthalocyanine polymers, with uniformly carboxylic end groups and carbonyl groups as bridges linking the phthalocyanine units, were successfully prepared. Structural modelling and atomic absorption spectroscopy confirmed the network polymeric structure and suggested at least nine phthalocyanine units in each polymeric network. The dielectric properties of the prepared polymers were investigated over a wide range of frequencies at room temperature. The electric modulus formalism was used to study the conductivity relaxation in the prepared polymers. The collapsing of the real part of the conductivity function, σ’, at higher frequencies for both materials was observed indicating that the local molecular dynamics is due to the polymer conjugated backbone (functional and/or terminal groups) with no clear effect of the central metal.

Synthesis, characterization, OFET and electrochemical properties of novel dimeric metallophthalocyanines

The synthesis of 4,4'-[6,6'-methylenebis (2-(2-(3,4-dicyanophenoxy)-5-methylbenzyl)-4-methyl-6,1-phenylene)] bis (oxy) diphthalonitrile 1 was achieved starting from 4-nitrophthalonitrile and 6,6'-methylenebis(2-(2-hydroxy-5-methylbenzyl)-4-methylphenol in DMF at 50 °C by the catalysis of K2CO3 under argon. The corresponding dimeric metallophthalocyanines (Zn2Pc2 2 and Co2Pc2 3) were tetramerized in dimethylaminoethanol with the appropriate metal salt. Newly synthesized compounds were characterized by elemental analysis, UV-vis, FT-IR (ATR), MALDI-TOF mass and (1)H-NMR spectroscopy techniques. The electrochemical properties of the complexes were examined by cyclic voltammetry, differential pulse voltammetry, controlled potential coulometry and in situ spectroelectrochemistry in nonaqueous media. The results showed that while there is considerable weak interactions between the two metal phthalocyanine units in dimeric zinc phthalocyanine, these interactions in dimeric cobalt phthalocyanine is remarkable. The catalytic performances of dimeric cobalt phthalocyanine in the reduction of oxygen in a medium similar to the working conditions of the polymer electrolyte membrane fuel-cells were found to be much higher than that of dinuclear zinc phthalocyanine. Solution-processed films of the complexes were utilized as an active semiconducting layer in the fabrication of organic field-effect transistors (OFETs) in the bottom-gate configurations. The output characteristics of the resulting p-type OFET devices were investigated to evaluate the performances such as the field effect mobility (μF). A relatively high field effect mobility of 7.3 × 10(-3) cm(2) V(-1) s(-1) was observed for dimeric cobalt phthalocyanine.

Photovoltaic and electrocatalytic properties of novel ball-type phthalocyanines bridged with four dicumarol

The new ball-type metallo bisphthalocyanines (Co(2)Pc(2) and Zn(2)Pc(2)) were synthesized from the corresponding [4,4'-bis(dicoumaroylphthalonitrile)] which can be obtained from the reaction of 3,3'-methylenebis(4-hydroxy-2H-chromen-2-one) and 4-nitrophthalonitrile. The structures of the newly synthesized compounds have been confirmed and characterized by elemental analysis, UV/Vis, IR and (1)H NMR spectroscopies and MALDI-TOF mass spectrometry. Solar cells of the configuration ITO/Co(2)Pc(2)/C60/Al and ITO/Zn(2)Pc(2)/C60/Al were fabricated. The effect of the thickness of the active Pc layer--the thickness of the Pc layer was varied from 15 to 80 nm--on solar cells parameters has been investigated. A nearly thickness independent open circuit voltage was observed in both structures. The maximum photovoltaic conversion efficiency, short circuit current and fill factor were observed in ITO/Zn(2)Pc(2)/C60/Al cell with 80 nm Pc layer to be 0.255%, 1 mA cm(-2) and 0.38, respectively. The redox properties of the ball-type complexes were investigated by cyclic voltammetry, controlled-potential coulometry and in situ spectroelectrochemistry in DMSO-TBAP. The electrochemical measurements showed that the complexes form ring-based and/or metal-based mixed-valence species, due to the remarkable intramolecular interactions between the two metal phthalocyanine units. The Vulcan XC-72(VC)/Nafion(Nf)/Co(2)Pc(2) modified glassy carbon electrode showed much higher catalytic performance towards oxygen reduction, compared to the VC/Nf/Zn(2)Pc(2) modified one. It was found that the VC/Nf/Co(2)Pc(2) catalyst is nearly insensitive to the presence of methanol. In the presence of 1 M methanol in the electrolyte, the catalytic performance of the Co(2)Pc(2)-based catalyst in oxygen reduction was much better than that of the Pt-based one. Thus, it was shown that the VC/Nf/Co(2)Pc(2) catalyst can be a good alternative to VC/Nf/Pt as a cathode catalyst in direct methanol fuel cells.

A pH-responsive fluorescent probe and photosensitiser based on a self-quenched phthalocyanine dimer

A self-quenched zinc(II) phthalocyanine dimer linked with an acid-sensitive ketal unit has been prepared, which can be activated in an acidic environment (pH = 5.0-6.5) as a result of the cleavage of the ketal linker and separation of the phthalocyanine units, resulting in enhanced fluorescence emission and singlet oxygen production.

Synthesis, Characterization, and Photoinduced Energy and Electron Transfer in a Supramolecular Tetrakis (Ruthenium(II) Phthalocyanine) Perylenediimide Pentad

Metal coordination was probed as a versatile approach for designing a novel electron donor/acceptor hybrid [PDIpy(4){Ru(CO)Pc}(4)] (1), in which four pyridines placed at the bay region of a perylenediimides (PDIpy(4)) coordinate with four ruthenium phthalocyanine units [Ru(CO)Pc]. This structural motif was expected to promote strong electronic coupling between the electron donors and the electron acceptor, a hypothesis that was confirmed in a full-fledged physicochemical investigation focusing on the ground and excited state reactivities. As far as the ground state is concerned, absorption and electrochemical assays indeed reveal a notable redistribution of electron density, that is, from the electron-donating [Ru(CO)Pc] to the electron-accepting PDIpy(4). The most important thing to note in this context is that both the [Ru(CO)Pc] oxidation and the PDIpy(4) reduction are rendered more difficult in 1 than in the individual building blocks. Likewise, in the excited state, strong electronic communication is the inception for a rapid charge-transfer process in photoexcited 1. Regardless of exciting [Ru(CO)Pc] or PDIpy(4), spectral characteristics of the [RuPc] radical cation (broad absorptive features from 425 to 600 nm with a maximum at 575 nm, as well as a band centered at 725 nm) and of the PDI radical anion (780 nm maximum) emerge. The correspondingly formed radical ion pair state lasts for up to several hundred picoseconds in toluene, for example. On the other hand, employing more polar solvents, such as dichloromethane, destabilizes the radical ion pair state.

Liquid crystalline phthalocyanine–fullerene dyads

Two phthalocyanine–C60 dyads 1 and 2 incorporating either a rigid or a flexible spacer between the phthalocyanine and fullerene units, respectively, have been prepared. Indeed, the nature of the spacer has proven to play an important role in the liquid crystalline properties of these compounds. Phthalocyanine–C60 dyad 2, containing a flexible spacer, self-organizes in columnar stacks within a rectangular arrangement. On the other hand, dyad 1 does not present mesomorphic properties on its own, but forms columnar hexagonal mesophases when blended with equimolar amounts of an intrinsically mesomorphic phthalocyanine.

Synthesis of Metallophthalocyanine Covalent Organic Frameworks That Exhibit High Carrier Mobility and Photoconductivity

A light COF: Two-dimensional covalent organic frameworks of a nickel phthalocyanine have been synthesized. Owing to well-ordered stacking of the phthalocyanine units, the resulting 2D framework provides enhanced and broad light absorbance and facilitates charge transport. The material becomes highly photoconductive and is exceptionally sensitive to deep-red visible and near-infrared light.

Ultra-fast charge transfer in organic electronic materials and at hybrid interfaces studied using the core-hole clock technique

The focus of this brief review is the use of resonant photoemission in its “core-hole clock” expression for the study of two important problems relevant for the field of organic electronics: the dynamical charge transfer across hybrid organic–inorganic interfaces, and the intermolecular charge transfer in the bulk of organic thin films. Following an outline of the technique, a discussion of its applicability and a short overview of experimental results obtained thus far, two examples are used to illustrate particular results relevant for the understanding of the charge transport in organic electronic devices. First, for Fe(II)-tetraphenylporphyrin molecules on semi-metallic molybdenum disulfide substrates, the electronic coupling to the substrate and the efficiency of charge transport across the interface different for the individual molecular electronic subsystems is discussed. And second, a discotic liquid crystalline material forming columnar assemblies is used to illustrate ultra-fast intermolecular charge transfer on the order of a few femtoseconds indicating an electronic coupling between the phthalocyanine units stronger than expected from the macroscopic charge transport characteristics of the material.

The in vivo efficacy of phthalocyanine–nanoparticle conjugates for the photodynamic therapy of amelanotic melanoma

The efficiency of a Zn(II)-phthalocyanine disulphide (C11Pc), a compound with both phthalocyanine units bearing seven hexyl chains and a sulphur terminated C11 chain, as a photodynamic therapy (PDT) agent was investigated in C57 mice bearing a sub-cutaneously transplanted amelanotic melanoma. The phthalocyanine was intravenously injected at a dose of 1.5 μmol/kg body weight either free or bound to gold nanoparticles, using a Cremophor emulsion as a delivery vehicle. Biodistribution studies at selected post-injection times showed that the nanoparticle-associated C11Pc was recovered in significantly larger amounts from all the examined tissues and the serum and yielded a greater selectivity of tumour targeting: thus, the ratio between the amount of phthalocyanine recovered from the amelanotic melanoma and the skin (peritumoural tissue) increased from 2.3 to 5.5 from the free to the gold nanoparticle-bound C11Pc at 24 h after injection. PDT studies with the C11Pc-loaded amelanotic melanoma showed a markedly more significant response of the tumour in the mice that had received the nanoparticle-bound photosensitiser; the PDT effect was especially extensive if the irradiation was performed at 3 h after C11Pc injection when large phthalocyanine amounts were still present in the serum. This suggests that the PDT promoted by C11Pc predominantly acts via vascular damage at least in this specific animal model. This hypothesis was fully confirmed by electron microscopy observations of tumour specimens obtained at different times after the end of PDT, showing an extensive damage of the blood capillaries and the endothelial cells.

Synthesis and electrochemical, in situ spectroelectrochemical, electrical and gas sensing properties of ball-type homo- and hetero-dinuclear phthalocyanines with four [1a,8b-dihydronaphtho[b]naphthofuro[3,2-d]furan-7,10-diyl] bridges

The new mono-nuclear Fe II 2 and ball-type homo-dinuclear Fe II–Fe II 3 phthalocyanines have been synthesized from the corresponding 4,4′-(1a,8b-dihydronaphtho[b]naphthofuro[3,2-d]-furan-7,10-diyl)bis(oxy)diphthalonitrile 1 while ball-type hetero-dinuclear Fe II–Co II phthalocyanine 4 was synthesized from 2. The compounds have been characterized by elemental analysis, UV–vis, IR and MALDI-TOF-mass spectroscopies. The redox behaviours of the complexes were identified by controlled-potential coulometry, cyclic voltammetry and differential pulse voltammetry measurements on Pt in dimethylsulfoxide containing tetrabutylammonium perchlorate. The assignments of the redox processes and the understanding of the interactions between the metal phthalocyanine units in 3 and 4 were achieved by the combined evaluation of the voltammetric and in situ spectroelectrochemical outcomes. Complex 3 showed ring-based mixed-valence behaviour as a result of the considerable interaction between the phthalocyanine rings. On the other hand, the interactions between the two metal phthalocyanine units of 4 were found to be much weaker than those in 3. The potential application of molecular organic semiconductors needs the control adjustment of conductivity. Ac and dc conductivity measurements were performed with the applied external electric filed. At high frequency, the conduction follows the universal power law and conduction mechanism can be explained by classical hopping barriers mechanism for the system.

Femtosecond Charge Transfer in Assemblies of Discotic Liquid Crystals

The electronic coupling strength within columns of discotic liquid crystals is investigated using core-level resonant photoemission spectroscopy. Coexisting well-ordered and disordered regions are identified in thin films of tetra-alkoxy-substituted phthalocyanines with the aid of near edge X-ray absorption fine structure and photoelectron spectroscopies. These different regions are used to derive a lower limit for the intermolecular charge transfer bandwidth within the framework of the core-hole clock principle. We find average charge transfer times on the order of a few femtoseconds, that is, significantly faster than the C(1s) core-hole lifetime, which indicates a surprisingly strong electronic coupling between the phthalocyanine units as compared to what is expected from the charge transport characteristics of this material.