Electrostatic self-organization of robust porphyrin-polyoxometalate films

Porphyrins and Polyoxometalate Scaffolds

Polyoxometalates (POMs) can act as unique reservoirs for multiple electron transfers. As POMs display only weak absorption in the visible spectrum, they can be associated with chromophores such as porphyrins and porphyrin antennae. In this Minireview, the research dedicated to the combination of porphyrins and polyoxometalates is put in context and the state of the art identifying the challenges addressed in the optimization of hybrid materials for applications is detailed.

Enhancement of photocurrent by incorporation of Preyssler type polyoxometalate protected nanoparticles in polyporphyrin films

The introduction of nanoparticles (MNPs) at the surface of cationic poly-porphyrin films, obtained by electrostatic interaction between the bis-porphyrin copolymer and the Preyssler type polyoxometalate P5W30@MNPs, enhances the photocurrent (up to 2.5-3 times greater as a function of the used nanoparticle).

Polymer matrix: A good substrate material for oxygen probes used in pressure sensitive paints

Over the past few years, surface pressure measurement has fundamental importance in many areas, particularly, aerodynamic research. Conventional methods involve pressure taps, but due to the nature of these pressure taps, only pressure information of isolated points on model surface is available, which limit their applications in aerodynamics studies. Recently the newly developed approach, pressure sensitive paint (PSP) has revolutionized such pressure measurements and various PSP materials have been developed for aerodynamics research. Hence, the main focus of this review is to study the interactions of polymers with different oxygen probes and polymeric role as supporting material in the maturation of PSP. In this review, the selected PSP materials are categorically elucidated in terms of their advantages and limitations to give a fair insight about their applicability. Further, we have summarized and articulated such particular optical oxygen sensing materials either that have been used as PSP or have potential to be used as PSP materials.

A Facile One-Pot Synthesis of Biomimetic Photocatalyst Zn(II)-Porphyrin-Sensitized 3D TiO2 Hollow Nanoboxes and Synergistically Enhanced Visible-Light Degradation

A serials of biomimetic photocatalyst zinc(II) meso-tetra(4-carboxyphenyl)porphyrinato (ZnTCP)-sensitized 3D hierarchical TiO2 hollow nanoboxes (TiO2-HNBs) assembled by six ordered nanosheets with dominant {001} facets exposure (ZnTCP@TiO2-HNBs) have been successfully synthesized by a facile one-pot solvothermal method via a topological transformation process with TiOF2 as template. Infrared spectra (IR), UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) confirmed that ZnTCP played a decisive role in constructing 3D hollow nanoboxes through the formation of ester bond combined to TiO2-HNBs, which also provided a transferring photo excited electrons bridge to sensitize TiO2-HNBs for enhancing visible-light response. Due to the superior sensitization and biomimetic activity of ZnTCP, the photodegradation rate of rhodamine B (RhB) of as-prepared ZnTCP@TiO2-HNBs with ZnTCP/TiOF2 mass ratio of 2% (T-2p) improves 3.6 times compared to that of TiO2-HNBs with a degradation yield of 99% for 2 h under simulated sunlight irradiation (> 420 nm). The enhanced photodegradation ability was attributed to synergistic visible photocatalytic mechanism of biomimetic catalyst, which can not only produce hydroxyl radical (•OH) and superoxide radical (•O2-) coming from the excitation process of ZnTCP sensitized TiO2-HNBs, but also generate singlet oxygen (1O2) that was only provided by biomimetic enzyme porphyrins. Furthermore, the photocatalyst showed good recycling stability and dispersibility after five rounds, ascribed to ZnTCP strong chemical bonding to the support TiO2-HNBs. By means of electrochemical cyclic voltammetry analysis, the effect of central zinc ions and parent porphyrin rings on the redox property of biomimetic catalyst was studied.

Synthesis and characterization of conjugated Dawson-type polyoxometalate-porphyrin copolymers

Hybrid polyoxometalate-porphyrin copolymeric films were obtained by the electro-oxidation of zinc octaethylporphyrin (ZnOEP) in the presence of a Dawson type polyoxophosphovanadotungstate bearing two pyridyl groups (POM(py)2). The synthesis of a series of POM(py)2 consisting of [P2W15V3O62](9-) functionalized with diol-amide or triol moieties, as well as the characterization of the copolymers are presented.

Self-organization of Zr(IV) porphyrinoids on graphene oxide surfaces by axial metal coordination

The protruding oxophilic central metal ion of Zr(IV) porphyrinoids facilitates axial coordination to the oxygen bearing functional groups on graphene oxide (GO) surfaces to result in new supramolecular photonic materials with high dye loading especially on edges and large defects. The reaction proceeds at room temperature with GO dispersed in tetrahydrofuran and GO films on glass. Since the Zr(IV) serves as a conduit, the photophysical properties of the dye sensitized GO derive from both the axially bound chromophores and the GO substrate. Self-organization of metalloporphyrinoids on GO mediated by axial coordination of group (IV) metal ions allows for direct sensitization of graphene and graphenic materials without requiring covalent chemistries with poorly conducting linkers.

Synthesis, electrochemical and photophysical properties of covalently linked porphyrin-polyoxometalates

Two covalently linked porphyrin-polyoxometalate hybrids have been prepared: an Anderson-type hexamolybdate [N(C(4)H(9))(4)](3)[MnMo(6)O(18){(OCH(2))(3)CNHCO(ZnTPP)}(2)] with two pendant zinc(II)-tetraphenylporphyrins, and a Dawson-type vanadotungstate [N(C(4)H(9))(4)](5)H[P(2)V(3)W(15)O(59){(OCH(2))(3)CNHCO(ZnTPP)}] with one porphyrin. Electrochemical studies show independent redox processes for the organic and inorganic parts at usual potentials. Photophysical studies reveal an electron transfer from the excited porphyrin to the Dawson polyoxometalate, but not to the Anderson polyoxometalate. Time resolved absorption spectroscopy allows the identification of the electron transfer pathways and the determination of the time constants.

Preparation and characterization of hydrophobic porphyrin nanoaggregates dispersed in polyvinyl alcohol films

It is known that among other applications porphyrin aggregates can be used in the detection of volatile organic compounds (VOC) and gases and vapors in general. However, the use of porphyrins for this purpose has been limited by the fact that usually the porphyrin and the polymer employed as a matrix are soluble in different media, such as polyvinyl alcohol and tetraphenylporphyrin, respectively. In this paper, we discuss how starting from stable aqueous solutions of hydrophobic porphyrins one can use the drop coating method to prepare polyvinyl alcohol polymer matrices containing porphyrin aggregates. The resulting solid films were characterized by optical techniques, and we have used UV-vis absorption spectroscopy to analyze how they interact with vapors of HCl , NO2 and NH3 .

Photostable self-cleaning cotton by a copper(II) porphyrin/TiO2 visible-light photocatalytic system

Thin films of meso-tetra(4-carboxyphenyl)porphyrinato copper(II) (CuTCPP) in conjunction with anatase TiO2 have been formed on cotton fabric. Their self-cleaning properties have been investigated by conducting photocatalytic degradation of methylene blue, coffee and wine stains under visible-light irradiation. CuTCPP/TiO2-coated cotton fabrics showed superior self-cleaning performance when compared to bare TiO2-coated cotton. Furthermore, CuTCPP/TiO2-coated fabrics showed significant photostability under visible-light as compared to free base TCPP/TiO2-coated fabrics. The fabrics were characterized by FESEM, XRD and UV-vis spectroscopy. An insight into the mechanistic aspects of the CuTCPP/TiO2 photocatalysis is also discussed. Visible-light driven self-cleaning cotton based on copper(II) porphyrin/TiO2 catalyst exhibits significant potential in terms of stability and reproducibility for self-cleaning applications.

Interfacial self-assembly and characterization of chiral coordination polymer multilayers with bidentate ligands of hydroquinine anthraquinone-1,4-diyl diether as linkers

Chiral coordination polymers (CPs) have been prepared at the air-water interface by using the ligand of 1,4-bis(9-O-dihydroquininyl)anthraquinone [(DHQ)2AQN] and its enantiomer of 1,4-bis(9-O-dihydroquinidinyl)anthraquinone [(DHQD)2AQN] as linkers and AgNO3 as the connector. Surface pressure-area isotherms indicated that both ligands could form insoluble monomolecular layers on the pure water and AgNO3 subphase surfaces. Compared with the average molecular area on the pure water surface, that of the ligand increased about 10% when its monolayer was formed on the AgNO3 subphase surface due to the formation of Ag-(DHQ)2AQN and Ag-(DHQD)2AQN chiral CPs. These monolayers were deposited on the quartz, Si, and indium tin oxide (ITO) substrate surfaces via the Langmuir-Blodgett (LB) method. The as-prepared LB films were characterized by using UV-vis absorption and fluorescence spectroscopy, circular dichroism and X-ray photoelectron spectroscopy, as well as by using a scanning electron microscope and atomic force microscope. Broad fluorescence emissions were measured at about 365 and 525 nm for the ligands in the methanol solutions. The second emission red shifted to about 555 nm in the LB films of both pure ligands and their Ag-directed CPs. A couple of well-reversible redox waves were recorded and centered at about -0.2 ~ -0.3 V (vs Ag/AgCl) for the ITO electrode covered by the LB films of (DHQ)2AQN, (DHQD)2AQN, or of the Ag(+)-directed CPs, which were designated to one electron transfer process of the ligands. Small aggregates were observed for the LB films prepared at the lower surface pressures, which were compressed to form more uniform two-dimensional layers at the higher surface pressures.

Preparation and characterization of SDS-stabilized hydrophobic porphyrinic nanoaggregates in water

Porphyrin nanoaggregates formed in the interior of colloidal suspensions can be considered as examples of supramolecular systems with self-organized architecture. Due to their peculiar optical and electrochemical properties such as decrease of fluorescence, increase of conductivity and possible electron transfer, these aggregates can be used in the design and fabrication of optoelectronic devices, such as organic solar cells and optical and electrochemical sensors. In this paper, we first describe the synthesis of a series of hydrophobic tetraphenylporphyrins by a change in the order of reagents addition that results in high yields of the desired products. These products were then employed to obtain stable suspensions of porphyrinic nanoaggregates in aqueous solutions of sodium dodecyl sulfate (SDS). The aggregates resulting of the encapsulation of the tetraphenylporphyrins into the micelles of the surfactant were studied by dynamic light scattering (DLS), atomic force microscopy (AFM) and UV-vis and fluorescence spectroscopies. The results indicate that the nanoggregates have a spherical morphology with particles whose average size ranges between 46–78 nm and ζ-potential values (higher than 55 mV), indicative of excellent stability. Optical characterization was used to determine the classification of nanoaggregates, according to the observed shifts on the absorption spectra.

Pd(II)-mediated triad multilayers with zinc tetrapyridylporphyrin and pyridine-functionalized nano-TiO2 as linkers: assembly, characterization, and photocatalytic properties

Triad hybrid multilayers containing the light sensitizers of zinc tetrapyridylporphyrin (ZnTPyP) and pyridine-functionalized TiO(2) (TiO(2)-Py) nanoparticles were constructed on substrate surfaces with the use of Pd(II) ions as the connectors using the layer-by-layer (LBL) method. The assembly process was monitored using ultraviolet-visible (UV-vis) absorption and X-ray photoelectron spectra as well as scanning electron microscopy and atomic force microscopy. The content of the pyridine substituents in the TiO(2)-Py nanocomposites was about 2% (w/w). The Soret absorption band of ZnTPyP was 24 nm red-shifted in the hybrid multilayers due to a strong intermolecular electronic coupling interaction among porphyrin macrocycles or porphyrin macrocycle/TiO(2)-Py nanoparticles. The average surface density of each ZnTPyP layer was about 1.4 × 10(-10) mol/cm(2). Aggregation of the small TiO(2)-Py nanoparticles to larger domains with sizes up to hundreds of nanometers occurred in the hybrid multilayers; however, such an aggregation behavior was weaker than that in the solutions. The quartz substrate modified with the as-prepared Pd/ZnTPyP/Pd/TiO(2)-Py triad hybrid multilayers was used as a heterogeneous photocatalyst for the degradation of methyl orange (MO) under irradiation (λ > 420 nm) at room temperature with a catalytic efficiency of about 1.3 × 10(-3) MO/ZnTPyP·s. Without the use of the filter, the catalytic efficiency increased because both ZnTPyP and TiO(2)-Py nanocomposites acted as the light sensitizers. It is suggested that the present heterogeneous catalyst has the advantages of facile separation, high stability, structural controllability on the molecular and nanoscale level, and good recyclability.

Responsive porphyrinoid nanoparticles: development and applications

The economy of space and materials and the continuously increasing demand for advanced functionalities for diverse technologies requires the development of new synthetic methods. Many nanomaterials have enhanced photophysical and photochemical properties in solutions and/or on surfaces, while others have enhanced chemical properties, compared to the atomic, molecular, or bulk phases. Nanomaterials have a wide range of applications in catalysis, sensors, photonic devices, drug delivery, and as therapeutics for treatment of a variety of diseases. Inorganic nanoparticles are widely studied, but the formation of organic nanomaterials via supramolecular chemistry is more recent, and porphyrinoids are at the forefront of this research because of their optical, chemical, and structural properties. The formation of nanoscaled materials via self-assembly and/or self-organization of molecular subunits is an attractive approach because of reduced energy requirements, simpler molecular subunits, and the material can be adaptive to environmental changes. The presence of biocompatible groups such as peptides, carbohydrates, polyglycols and mixtures of these on the periphery of the porphyrin macrocycle may make nanoparticles suitable for therapeutics. This perspective focuses on responsive, non-crystalline porphyrinoid nanomaterials that are less than about 100 nm in all dimensions and used for catalytic or therapeutic applications.

Layer-by-layer assembly and characterization of multilayers of a manganese porphyrin linked poly(4-vinylpyridinium) derivative and poly(styrenesulfonic acid-o-maleic) acid

Multilayers of manganese(III) porphyrin-linked poly(vinylpyridinium) (MnTMPyP-PVPMe) polyelectrolyte and poly(styrenesulfonic acid-o-maleic) acid (PSS) have been assembled on gold, quartz, and indium tin oxide surfaces by a layer-by-layer (LBL) technique. The assembly process was monitored by measuring their absorption spectra and frequency change after each assembly, both of which confirmed the formation of three-dimensional MnTMPyP-PVPMe/PSS multilayers. The Soret absorption band of porphyrin red shifted about 8 nm in the multilayer compared with that in the dilute aqueous solution. The average mass changes for each assembly of MnTMPyP-PVPMe and PSS were estimated to be about 2.9 and 0.25 μg/cm(2), respectively. X-ray photoelectron spectra revealed that the as-prepared multilayers were composed of S 2p, C 1s, N 1s, O 1s, and Mn 2p, corresponding to polymers of MnTMPyP-PVPMe and PSS. A rough surface was observed after the assembly of MnTMPyP-PVPMe on the gold surface, but it became smoother when the PSS layer was adsorbed. The significant difference in the mass change and film morphology after the assembly of MnTMPyP-PVPMe compared to those after the assembly of PSS was ascribed to the reason that the MnTMPyP-PVPMe polyelectrolyte contained large metalloporphyrin macrocycles, which were axially coordinated to the pyridyl substituents of the PVP polymeric backbones. The cyclic voltammograms revealed two couples of redox waves in the phosphate electrolyte solution at pH 11, which corresponded to the electron-transfer processes of Mn(II)/Mn(III) and Mn(III)/Mn(IV) of polymeric manganese porphyrin MnTMPyP-PVPMe. The charge-transfer process was also investigated. Finally, the present MnTMPyP-PVPMe/PSS multilayers were used as a heterogeneous catalyst for the decoloration of an azo dye.

Formation of a hybrid compound composed of a saddle-distorted Tin(IV)-porphyrin and a Keggin-type heteropolyoxometalate to undergo intramolecular photoinduced electron transfer

Nonplanar Sn(IV)-porphyrin complexes, [Sn(TMPP(Ph)(8))-Cl(2)] (1) and [Sn(TMPP(Ph)(8))(OMe)(2)] (2) (TMPP(Ph)(8): 5,10,15,20-tetrakis(4-methoxyphenyl)-2,3,7,8,12,13,17,18-octaphenylporphyrinato), were prepared and characterized by spectroscopic and electrochemical methods together with X-ray crystallography. Variable-temperature (1)H NMR study revealed that the coordination of the methoxo ligand of 2 is weak enough in solution to enhance the axial ligand exchange with a Keggin-type phosphotungstate (α-[PW(12)O(40)](3-)) due to the steric stress between the axial methoxo ligand and the peripheral phenyl groups of the porphyrin ligand. The formation of a novel 1:1 donor-acceptor complex, [Sn(TMPP(Ph)(8))(OMe)(α-[PW(12)O(40)])](2-) (4) was confirmed by (1)H NMR and UV-vis spectral titrations, and also by MALDI-TOF-MS measurements. Electrochemical measurements for the donor-acceptor complex in PhCN revealed that the Sn(IV)-TMPP(Ph)(8) moiety acts as an electron donor and the α-[PW(12)O(40)](3-) moiety acts as an electron acceptor and that the energy level of the electron-transfer (ET) state of the 1:1 complex (1.17 eV) is lower than that of the triplet excited states of the SnTMPP(Ph)(8) complex (1.31 eV). Femtosecond and nanosecond laser flash photolysis measurements indicate that intersystem crossing from the singlet excited sate to the triplet excited state occurs followed by intramolecular photoinduced electron transfer from the triplet excited state of the Sn(IV)-TMPP(Ph)(8) moiety to the α-[PW(12)O(40)](3-) moiety in the 1:1 complex in benzonitrile.

Formation and photocatalytic properties of nanocomposite films containing both tetracobalt Dawson-derived sandwich polyanions and tetracationic porphyrins

Films based on electrostatic interactions between tetracationic zinc porphyrins, ZnOEP(py)(4)(4+) or ZnTMePyP(4+), and the tetracobalt Dawson-derived sandwich polyanion αββα-[Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](16-) are formed by the so-called layer-by-layer method. These films have been characterized by UV-visible absorption spectroscopy, atomic force microscopy and electrochemistry. The composition of the film was measured by X-ray photoelectron spectrum (XPS). The XPS data confirm the presence of the expected elements. The photocatalytic properties of these films have been also studied for the reduction of silver and gold ions. Indeed, in these systems, porphyrins can be excited by visible light and then play the role of photosensitizers able to give electrons to POM known to be good catalysts. Silver nanowires and gold nanosheets have been obtained.

Porphyrins as Molecular Electronic Components of Functional Devices

The proposal that molecules can perform electronic functions in devices such as diodes, rectifiers, wires, capacitors, or serve as functional materials for electronic or magnetic memory, has stimulated intense research across physics, chemistry, and engineering for over 35 years. Because biology uses porphyrins and metalloporphyrins as catalysts, small molecule transporters, electrical conduits, and energy transducers in photosynthesis, porphyrins are an obvious class of molecules to investigate for molecular electronic functions. Of the numerous kinds of molecules under investigation for molecular electronics applications, porphyrins and their related macrocycles are of particular interest because they are robust and their electronic properties can be tuned by chelation of a metal ion and substitution on the macrocycle. The other porphyrinoids have equally variable and adjustable photophysical properties, thus photonic applications are potentiated. At least in the near term, realistic architectures for molecular electronics will require self-organization or nanoprinting on surfaces. This review concentrates on self-organized porphyrinoids as components of working electronic devices on electronically active substrates with particular emphasis on the effect of surface, molecular design, molecular orientation and matrix on the detailed electronic properties of single molecules.