pH-dependent electron transfer from re-bipyridyl complexes to metal oxide nanocrystalline thin films

Photoinduced interfacial electron transfer (ET) from molecular adsorbates to semiconductor nanoparticles has been a subject of intense recent interest. Unlike intramolecular ET, the existence of a quasicontinuum of electronic states in the solid leads to a dependence of ET rate on the density of accepting states in the semiconductor, which varies with the position of the adsorbate excited-state oxidation potential relative to the conduction band edge. For metal oxide semiconductors, their conduction band edge position varies with the pH of the solution, leading to pH-dependent interfacial ET rates in these materials. In this work we examine this dependence in Re(L(P))(CO)3Cl (or ReC1P) [L(P) = 2,2'-bipyridine-4,4'-bis-CH2PO(OH)2] and Re(L(A))(CO)3Cl (or ReC1A) [L(A) = 2,2'-bipyridine-4,4'-bis-CH2COOH] sensitized TiO2 and ReC1P sensitized SnO2 nanocrystalline thin films using femtosecond transient IR spectroscopy. ET rates are measured as a function of pH by monitoring the CO stretching modes of the adsorbates and mid-IR absorption of the injected electrons. The injection rate to TiO2 was found to decrease by 1000-fold from pH 0-9, while it reduced by only a factor of a few to SnO2 over a similar pH range. Comparison with the theoretical predictions based on Marcus' theory of nonadiabatic interfacial ET suggests that the observed pH-dependent ET rate can be qualitatively accounted for by considering the change of density of electron-accepting states caused by the pH-dependent conduction band edge position.     

Porphyrins. 9. New data on the polyformylation of metal complexes of etioporphyrin I

The structures of the products of the polyformylation of Cu, Ni, and Co complexes of etioporphyrin (EP) as monoformyl-, ,-diformyl-, ,-diformyl-, and ,,-triformyl-EP were established by electronic, IR, and PMR spectroscopy and mass spectrometry. -Formyl--(N-methylformaldimine)-EP and porphyrins that contain a cyclopentane ring can be formed by alkaline treatment of the Vilsmeier formylation products.See [1] for communication 8.See [2] for our preliminary communication.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 767–775, June, 1979.     

Isostructural copper-zinc mixed metal complexes for single source deposition of Cu-ZnO composite thin films

The mixed metal complex [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Br]·THF (1) and its isostructural analogues ([Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Cl]·THF (2) and [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)Cl/Br]·THF (3)) have been prepared by a simple metal ligand assembly method and were characterized by their melting points, elemental analysis, IR spectroscopy, thermogravimetry and single crystal X-ray structures. The compounds are distinguished only by the nature of the halide ions and are made up of the same [Zn(TFA)(3)(μ-OH)Cu(3)(dmae)(3)X]·THF molecular building block with Cu(3)ZnO(4) cubane moieties as the central core in which the four metal ions and four oxygen atoms are joined together in alternate positions of the cuboid. All the complexes crystallize with similar packing and crystallographically related symmetry settings, distinguished mainly by the degree of disorder within the complexes and the ordering of the complexes in the structures. The triclinic cell of (1) emulates the monoclinic cell of (2) and is pseudomerohedrally twinned by a symmetry operation of the monoclinic cell. The molecules in (2) are 1:1 disordered around a crystallographic mirror plane. The structure of the mixed halogen compound (3) in turn is a superstructure of the less symmetric structures of (1) and (2) formed by ordering of the complexes along the longest axis of (3). Aerosol-assisted chemical vapour deposition (AACVD) experiments showed that they are promising precursors to deposit thin films of crystalline Cu/ZnO composites. The surface morphology, microstructure, chemical composition and crystallinity of the resulting Cu/ZnO composite thin films were analysed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDAX), which suggest that the films are thin, crystalline, uniform, smooth and tightly adherent to the substrates with average crystallite sizes in a range between 40.2 and 80.0 nm. Particle sizes, shapes and film morphology were investigated as a function of precursor and decomposition temperature.     

Synthesis of copper and iron complexes of meso-substituted etioporphyrin derivatives

The synthesis of the copper complex of meso-cyanoetioporphyrin I has been effected from the corresponding meso-formyl derivative and meso-formyletiohemin. An intermediate compound of the copper complex of etioporphyrin I with the Vilsmeier complex (DMFA-POCl₃) has been isolated, and it has been reduced to the copper complex of dimethylamino-methyletioporphyrin I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1172–1175, September, 1973.     

Transition metal dichalcogenide thin films for solar hydrogen production

In the last three decades, transition metal dichalcogenides (TMDs) have been extensively studied for electronic, photonic, and energy applications. Different efforts are directed to find a holy grail of efficient and economically feasible materials that could be simple in production and available on a large scale. The interest in TMDs (MoS₂, WS₂, MoSe₂, WSe₂) stems from their suitable electronic structure for efficient solar light absorption and simple exfoliation technique of 2D crystallites due to the van der Waals bonding of these materials. This led to various designs and combinations of 2D single layers that could form heterojunctions and multijunctions for efficient light absorption, charge carrier generation/separation, and its transfer in optoelectronic and energy harvesting devices. Herein, TMD thin films are reviewed as photoelectrodes for solar hydrogen evolution and compared to that of other more developed materials.     

Electrical and magnetic properties of thin films containing metal clusters

A large variety of granular polymer thin films can be synthetized in a capacitively coupled coplanar diode radiofrequency (r.f.) discharge system in which an argon-monomer mixture is injected at low pressure (20 mTorr). This approach offers several advantages over the other techniques, e.g. easy control of the metal content in the film from a few % up to 100%. The d.c. electrical properties of gold containing plasma polymerized tetrafluoroethylene (PPTFE) and the magnetic behavior of cobalt containing plasma polymerized propane (PPP) are reported in this paper.     

Tungsten imido complexes as precursors to tungsten carbonitride thin films

Thin films of tungsten carbonitride have been formed on glass by low-pressure chemical vapour deposition (LP)CVD at 550 degrees C from four closely related precursors: [W(mu-N(t)Bu)(N(t)Bu)Cl(2)(H(2)N(t)Bu)](2), [W(N(t)Bu)(2)Cl(2)(TMEDA)] (TMEDA = N,N,N',N'-tetramethylethylenediamine), [W(N(t)Bu)(2)Cl(2)(py)(2)] (py = pyridine) and [W(N(t)Bu)(2)Cl(N{SiMe(3)}(2))]. The grey mirror-like films were grown with a nitrogen or ammonia bleed gas. In all cases the chlorine content of the deposited films was less than 1 at% and the oxygen content of the films was lower for those grown using ammonia. Surprisingly, the use of ammonia did not significantly change the carbon content of the resulting films. Despite the coordination environment around the metal being essentially the same and the materials having a comparable volatility, some differences in film quality were observed. The films were uniform, adhesive, abrasion resistant, conformal and hard, being resistant to scratching with a steel scalpel. X-Ray powder diffraction patterns of all the films showed the formation of beta-WN(x)C(y). As a comparison the aerosol-assisted chemical vapour deposition (AA)CVD of [W(mu-N(t)Bu)(N(t)Bu)Cl(2)(H(2)N(t)Bu)](2) was investigated and amorphous tungsten carbonitride films were deposited.     

Multilayered ordering of the metal nanoparticles in polymer thin films under photoirradiation

Interference light-induced photogeneration of metal nanoparticle in polymer films was explored. The nanoparticle was obtained from metal complex homogeneously dispersed in the film. Standing waves resulting from light interference were generated by irradiating nearly monochromatic light to the sample placed on a reflective substrate. During irradiation metal nanoparticles were developed by photoreduction of the metal complexes forming layers rich with particles. These nanoparticle-enriched layers were found to align in parallel to the reflective substrate, and they were separated from each other by a constant spacing. This layer spacing was varied by changing the wavelength and/or the incident angle of the irradiating light. The observed results show that the spatial distribution of the nanoparticles is determined by the optical interference within the film. Surprisingly, regions exist between the nanoparticle-enriched layers where the metal species are not detected. Such regions extends for distances larger than tens of nanometers. This means that the metal complexes initially homogeneously dispersed within the polymer were transported away from certain regions upon photoirradiation. The metal precursors are preferentially photoreduced into the metal nanoparticles at the constructive interference regions. The spatially varying consumption rates of the precursors are considered to lead a concentration gradient, thereby causing a directional diffusion of the unreduced precursors toward the regions where constructive interference occurs.     

Gas sensing mechanism in chemiresistive cobalt and metal-free phthalocyanine thin films

The gas sensing behaviors of cobalt phthalocyanine (CoPc) and metal-free phthalocyanine (H2Pc) thin films were investigated with respect to analyte basicity. Chemiresistive sensors were fabricated by deposition of 50 nm thick films on interdigitated gold electrodes via organic molecular beam epitaxy (OMBE). Time-dependent current responses of the films were measured at constant voltage during exposure to analyte vapor doses. The analytes spanned a range of electron donor and hydrogen-bonding strengths. It was found that, when the analyte exceeded a critical base strength, the device responses for CoPc correlated with Lewis basicity, and device responses for H2Pc correlated with hydrogen-bond basicity. This suggests that the analyte-phthalocyanine interaction is dominated by binding to the central cavity of the phthalocyanine with analyte coordination strength governing CoPc sensor responses and analyte hydrogen-bonding ability governing H2Pc sensor responses. The interactions between the phthalocyanine films and analytes were found to follow first-order kinetics. The influence of O2 on the film response was found to significantly affect sensor response and recovery. The increase of resistance generally observed for analyte binding can be attributed to hole destruction in the semiconductor film by oxygen displacement, as well as hole trapping by electron donor ligands.     

Second-order non-linear optical response in LB films for the metal complexes

The complexes with long alkyl chains {[Fe(C₁₆-trz)₃](ClO₄)₂}_n (1), [Fe(C₁₅-BPT)₂(NCS)₂] (2), [Fe(C₁₆-salen)Cl] (3), [Fe(C₁₆-salmmen)Cl] (4), K[Fe(C₁₆-salen)(CN)₂] (5), K[Fe(C₁₆-salmmen)(CN)₂] (6), Na[Fe(C₁₆-salmmen)(CN)₂] (7), [Mn(C₁₆-salen)Cl] (8), [Ni(C₁₆-salen)] (9), [Cu(C₁₆-salen)] (10) were synthesized (C₁₆-trz = 4-hexadecyl-1,2,4-triazole, C₁₅-BPT = N-(3,5-di-2-pyridinyl-4H-1,2,4-triazol-4-yl)-hexadecanecarboxamide, C₁₆-salen = N,N-bis[4-(hexadecyloxy)salicylidene]ethylenediamine, C₁₆-salmmen = N,N′-bis[4-(hexadecyloxy)salicylidene]-1,2-diaminopropane). Langmuir–Blodgett (LB) films of compounds 1–10 were prepared (Scheme 1). The transfers of the molecules from onto the gas–water surface to glass substrate were confirmed by UV–Vis spectra. The second harmonic generation (SHG) were estimated for the LB films formed by the metal complexes. The SHG was observed for the complexes with the long alkyl chains in LB film. The order of the intensity for the SHG related with the number of unpaired d electrons or the d electron configurations.     

Electrical and mechanical properties of thin metal films: Size effects

A general expression for the function of electron scattering in thin films of a grain structure is derived which takes account of both the external and internal size effects. Limiting and particular values of this function are given for polycrystalline and single-crystal films. Theoretical results are compared to the experimental results obtained for aluminium and tin. The relationship between size effects and resistivity, temperature coefficient of resistance, longitudinal and transverse strain coefficient of resistance and thermoelectric power is studied. The dependence of the orientation of monocrystalline copper and aluminium films on thermal stress, the direction of the energy density of elastic strains and the anistropy of elastoresistance coefficients in these films are examined. An expression for the gauge factor in single-crystal metal films of given orientations is derived.     

Enhanced conductivity of thin film polyaniline by self-assembled transition metal complexes

In a recent study, the transition metal complex, cis-dichlorobis(2-,2'-dipyridyl)ruthenium (II) (Ru(bpy)2Cl2), and the macrocycle Ru(TPP)CO (TPP:- tetraphenylporphine) were bound to pyridine terminated self-assembled monolayers on quartz. Following modification of the quartz surface with metal complexes, the conducting polymer polyaniline was deposited via in situ polymerization. The sheet conductivity (as measured by the four-probe method) of the resulting polyaniline films deposited onto Ru(bpy)2Cl2 and Ru(TPP)CO surfaces was significantly enhanced relative to films deposited onto unmodified quartz. It is postulated that either the macrocycle or the transition metal complex-modified surface interacts with the conducting polymer as it is forming, resulting in a more ordered expanded coil conformation for the polymer. The net result of such an interaction is a thin film possessing significantly greater electrical conductivity.     

Donnan effects in the steady-state diffusion of metal ions through charged thin films

The steady-state diffusion of metals ions through thin films with fixed charged groups was investigated using diffusive gradients in thin films (DGT) measurements. Copolymers of acrylamide and sodium acrylate cross-linked with N,N'-methylenebisacrylamide were used as diffusive gels. The rate of diffusion of cadmium ions through the gels was measured by determining the mass of cadmium bound to a backing chelex resin after a known deployment time. Variation of the ionic strength as well as the fixed charge density and the thickness of the gel layer allowed evaluation of the impact of the Donnan partitioning and the diffusion layer in solution on the observed steady-state flux of ions through the layer. The results underscore that, as the Donnan partitioning increases, the impact of the diffusion layer in solution becomes more significant. At modest Donnan potentials, Donnan partitioning controls the net flux of metal ions, whereas at conditions of increasing Donnan potential, i.e., at decreasing ionic strength, the flux is increasingly limited by diffusion in solution. An analytical expression is developed to describe the influence of Donnan partitioning on the observed steady-state flux of metal ions.     

Conducting LB films based on metal complexes of sulphur donor ligands

Preliminary studies are reported on the film forming characteristics of compounds such as dialkyldimethylammonium-M (dmit)₂ and dialkyldimethylammonium-M (mnt)₂ where M = Ni, Pt or Pd. All materials investigated show good monolayer behaviour and deposit readily onto evaporated aluminium or gold films. This is confirmed by surface potential and FTIR measurements. The lateral conductivity of deposited films increases by many orders of magnitude when exposed to bromine vapour.     

Rapid fabrication of metal organic framework thin films using microwave-induced thermal deposition

We have demonstrated a novel method to rapidly fabricate nanoporous MOF thin films and patterns on porous alumina substrates under microwave irradiation.     

Formation of solvent cages around organometallic complexes in thin films of supported ionic liquid

The first experimental evidence for the formation of ordered three-dimensional structures in solutions of organometallic complexes in a thin film of supported ionic liquid was obtained. The ordering effect leads to drastically reduced mobility of ionic liquid and complex molecules.