Metalloporphyrin assemblies on pyridine-functionalized titanium dioxide

Anatase Nanocrystals Covalently Functionalized with EDTA-diol: Interaction with Aromatic Sulfur

The current study addresses the generation of surface-modified nanograined anatase (5 nm) by a single-step in situ process. The EDTA-diol (ester) functionality existing on the surface of anatase nanoparticles was proved with the help of a battery of physicochemical techniques, including FTIR, XPS, and NMR spectral measurements. The sample showed excellent dispersity in ethanol. The anatase lattice showed disorder and had oxygen vacancies. From the XPS analysis, the existence of 14% of Ti³⁺ was established. The functionalized sample remained thermally stable up to 250 °C, beyond which it transformed into a graphite-titania nanocomposite. The interfacial ligand (ester) to metal (Ti) charge transfer (LMCT) transitions were present in the UV-visible spectrum of the sample and indicated the functionalization to be covalent. Unsaturated OH-groups on the surface yielded a ζ-potential value of -39.8 mV. The covalently functionalized nanotitania was exploited in the adsorptive desulfurization of thiophene, an aromatic sulfur model compound. The consequences of surface adsorption of thiophene were analyzed with the help of UV-visible, FTIR, and ¹H and ¹³C NMR spectra and EDS and XPS measurements. The adsorption data, derived from the batch process, were fitted successfully to pseudo-second-order kinetics and the Temkin model. The adsorption capacity of covalently functionalized titania was compared with several other high surface area adsorbents containing thiophilic metal ions.

Theoretical design of metal-phthalocyanine dye-sensitized solar cells with improved efficiency

The present work carried out a theoretical study of the electronic structures, absorption spectra, and photovoltaic performance of two series of transition metal-phthalocyanine derived from nonperipheral electron-donating substituents, either (2-phenyl) phenoxy(M-PC1) or quinoleinoxy(M-PC2). The DFT and TD-DFT were employed for this study. The effect of modifying the central metal atoms and the substitution on cell performance were investigated in terms of polarizability (α), hyper-polarizability (β), chemical potential (μ), chemical hardness (η), electrophilicity power (ω), FMOs, energy gaps, UV/vis absorption spectra and injected driving force (ΔG^inject), light harvesting efficiencies (LHE), total reorganization energy (λ_tot), open circuit photovoltage (V_oc), and life time of the excited state (τ). The results obtained by using these parameters showed that the replacement of (2-phenyl) phenoxy by a proposed substituent such as quinoleinoxy would increase the hyper-polarizability, light harvesting efficiency, and open circuit photovoltage, while on the other hand the reorganization energy and the injection driving force are decreased. Modifying central metal atoms, such as Zn, Cd, Pd, and Pt, exhibited good performance in terms of the driving force of electron injection, charge transfer characteristics, and dye reorganization as compared with the Cu reference dye. The findings provided a useful prediction and perspective for the promising future for high-efficiency dye-sensitized solar cells (DSSCs) with dyes based on phthalocyanine. Graphical abstract Photovoltaic performance of Metallo-phthalocyanine contening (2-phenyl) phenoxy and quinoleinoxy.

Multimolecular assemblies on high surface area metal oxides and their role in interfacial energy and electron transfer

High surface area metal oxides offer a unique substrate for the assembly of multiple molecular components at an interface.

Electron injection dynamics in high-potential porphyrin photoanodes

There is a growing need to utilize carbon neutral energy sources, and it is well known that solar energy can easily satisfy all of humanity's requirements. In order to make solar energy a viable alternative to fossil fuels, the problem of intermittency must be solved. Batteries and supercapacitors are an area of active research, but they currently have relatively low energy-to-mass storage capacity. An alternative and very promising possibility is to store energy in chemical bonds, or make a solar fuel. The process of making solar fuel is not new, since photosynthesis has been occurring on earth for about 3 billion years. In order to produce any fuel, protons and electrons must be harvested from a species in its oxidized form. Photosynthesis uses the only viable source of electrons and protons on the scale needed for global energy demands: water. Because artificial photosynthesis is a lofty goal, water oxidation, which is a crucial step in the process, has been the initial focus. This Account provides an overview of how terahertz spectroscopy is used to study electron injection, highlights trends from previously published reports, and concludes with a future outlook. It begins by exploring similarities and differences between dye-sensitized solar cells (DSSCs) for producing electricity and a putative device for splitting water and producing a solar fuel. It then identifies two important problems encountered when adapting DSSC technology to water oxidation-improper energy matching between sensitizer energy levels with the potential for water oxidation and the instability of common anchoring groups in water-and discusses steps to address them. Emphasis is placed on electron injection from sensitizers to metal oxides because this process is the initial step in charge transport. Both the rate and efficiency of electron injection are analyzed on a sub-picosecond time scale using time-resolved terahertz spectroscopy (TRTS). Bio-inspired pentafluorophenyl porphyrins are promising sensitizers because their high reduction potentials are compatible with the energy requirements of water oxidation. TRTS of free-base and metalated pentafluorophenyl porphyrins reveal inefficient electron injection into TiO2 nanoparticles but more efficient electron injection into SnO2 nanoparticles. With SnO2, injection time scales depend strongly on the identity of the central substituent and are affected by competition with excited-state deactivation processes. Heavy or paramagnetic metal ions increase the electron injection time scale by roughly one order of magnitude relative to free-base or Zn(2+) porphyrins due to the possibility of electron injection from longer-lived, lower-lying triplet states. Furthermore, electron injection efficiency loosely correlates with DSSC performance. The carboxylate anchoring group is commonly used to bind DSSC sensitizers to metal oxide surfaces but typically is not stable under the aqueous and oxidative conditions required for water oxidation. Electron injection efficiency of several water-stable alternatives, including phosphonic acid, hydroxamic acid, acetylacetone, and boronic acid, were evaluated using TRTS, and hydroxamate was found to perform as well as the carboxylate. The next challenge is incorporating a water oxidation catalyst into the design. An early example, in which an Ir-based precatalyst is cosensitized with a fluorinated porphyrin, reveals decreased electron injection efficiency despite an increase in photocurrent. Future research will seek to better understand and address these difficulties.

Dye-sensitized solar cells based on multichromophoric supramolecular light-harvesting materials

Dye-sensitized solar cells comprised of supramolecular light-harvesting zinc-phthalocyanine⋯peryleneimide dyads on TiO₂ films generate photoelectricity throughout the 300–650 nm region with the power conversion efficiency reaching up to 2.3% and the incident-photon-to-current-efficiency up to 40% under one-sun conditions.

Effects of benzo-annelation of asymmetric phthalocyanine on the photovoltaic performance of dye-sensitized solar cells

Novel highly asymmetric zinc tetraazaporphyrin (TAP) derivatives (Zn-tri-TAPNc and Zn-tri-PcNc) with one carboxyl and three tert-butyl peripheral substituent groups for dye-sensitized solar cells were synthesized.

Functionalized ceramics for biomedical, biotechnological and environmental applications

Surface functionalization has become of paramount importance and is considered a fundamental tool for the development and design of countless devices and engineered systems for key technological areas in biomedical, biotechnological and environmental applications. In this review, surface functionalization strategies for alumina, zirconia, titania, silica, iron oxide and calcium phosphate are presented and discussed. These materials have become particularly important concerning the aforementioned applications, being not only of great academic, but also of steadily increasing human and commercial, interest. In this review, special emphasis is given to their use as biomaterials, biosensors, biological targets, drug delivery systems, implants, chromatographic supports for biomolecule purification and analysis, and adsorbents for toxic substances and pollutants. The objective of this review is to provide a broad picture of the enormous possibilities offered by surface functionalization and to identify particular challenges regarding surface analysis and characterization.

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.

Porphyrins and phthalocyanines in solar photovoltaic cells

This review summarizes recent advances in the use of porphyrins, phthalocyanines, and related compounds as components of solar cells, including organic molecular solar cells, polymer cells, anddye-sensitized solar cells. The recent report of a porphyrin dye that achieves 11% power conversion efficiency in a dye-sensitized solar cell indicates that these classes of compounds can be as efficient as the more commonly used ruthenium bipyridyl derivatives.

Preparation, size control, surface deposition, and catalytic reactivity of hydrophobic corrolazine nanoparticles in an aqueous environment

Nanoparticles, each consisting of one of the three molecular corrolazine (Cz) compounds, H(3)(TBP(8)Cz), Mn(III)(TBP(8)Cz), and Fe(III)(TBP(8)Cz) (TBP(8)Cz = octakis(4-tert-butylphenyl)corrolazinato), were prepared via a facile mixed-solvent technique. The corrolazine nanoparticles (MCz-NPs) were formed in H(2)O/THF (10:1) in the presence of a small amount of a polyethylene glycol derivative (TEG-ME) added as a stabilizer. This technique allows highly hydrophobic Czs to be "dissolved" in an aqueous environment as nanoparticles, which remain in solution for several months without visible precipitation. The MCz-NPs were characterized by UV-visible spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM) imaging, and shown to be spherical particles from 100-600 nm in diameter with low polydispersity indices (PDI = 0.003-0.261). Particle size is strongly dependent on Cz concentration. The H(3)Cz-NPs were adsorbed on to a modified self-assembled monolayer (SAM) surface and imaged by atomic force microscopy (AFM). Adsorption resulted in disassembly of the larger H(3)Cz-NPs to smaller H(3)Cz-NPs, whereby the resulting particle size can be controlled by the surface energy of the monolayer. The Fe(III)Cz-NPs were shown to be competent catalysts for the oxidation of cyclohexene with either PFIB or H(2)O(2) as external oxidant. The reactivity and product selectivity seen for Fe(III)Cz-NPs differs dramatically from that seen for the molecular species in organic solvents, suggesting that both the nanoparticle structure and the aqueous conditions may contribute to significant changes in the mechanism of action of the Fe(III)Cz catalyst.

Immobilization of zinc porphyrin complexes on pyridine-functionalized glass surfaces

In order to immobilize sublimable and fluorescent dye molecules on transparent surfaces for the detection of far field molecular interference experiments, we investigate the potential of pyridine-functionalized glass substrates as coordination sites for the zinc complex of tetraphenylporphyrin (ZnTPP). Borosilicate glass is functionalized with 4-(6-(ethoxydimethylsilyl)hexyloxy)pyridine in order to cover the glass surface with pyridine subunits. ZnTPP molecules are deposited by sublimation through mechanical masks of various sizes in a high-vacuum chamber. The resulting micropatterns are analyzed using epifluorescence microscopy which also allows us to define a measure for the quality of molecular immobilization. We observe a reduced mobility and an increased efficiency for the trapping of ZnTPP on pyridine-functionalized surfaces.