Polymer-metal complex film

New Photodiode Composed of a Polymer-metal Complex Film... 

Conductive polymers are useful semiconductors or coating materials to construct solar cells. A new photodiode is proposed to be made from a film of a polymer metal complex. Immobilized catalysts on polymers are used for solar energy storage systems. 

In the second approach, metal-ion/complex was first attached to one of the polymer blocks. A thin film of the resulting polymer metal complex was then obtained by spin coating/solution casting. Alternatively, the polymer metal complex may also be dissolved in a suitable solvent system that selectively dissolves one of the blocks. Micelles or nanosized aggregates formed in this case. The micellization of amphiphilic block copolymers and their use in the formation of metal nanoparticles has been discussed previously.44 A monolayer of micelles was introduced on a substrate surface by dipping or electrostatic attraction. The substrate was then subjected to further chemical or physical treatments as mentioned earlier. The third approach involves the formation of micelles from the metal-free block copolymer in a suitable solvent system. The micelle solution was then added with metal ion, which was selectively coordinated to one of the blocks. These micelle-metal complexes can also be processed by a procedures similar to the second approach. 

Polymer metal complex formation of different polyvinylpyridines in solution, in hydrogels and at interfaces were investigated [83]. In aqueous solution linear or crosslinked polyvinylpyridines in the interaction with H2PtCl6 results in reduced viscosities and reduces swelling coefficients, respectively. Complexation leads to molecular bridges and folding of the polymer. Film formation was observed at the interface of poly(2-vinylpyridine) dissolved in benzene and metal salts dissolved in water. 

Porphyrins, phthalocyanines, hemiporphyrazines and tetraazaannulenes were intensively investigated as cyclic ligands for polymer metal complexes [31,32]. The polymeric chelates are generally obtained as insoluble brown-to-black powders. In some cases for device construction film formation during the preparation process was achieved. 

A pH titration of Cu(II)-PVA complex indicated that four hydroxyl groups combined with one Cu(II) ion above pH 7.3 [14]. The Cu(II)-PVA complex in aqueous solution had absorption bands at 640 nm (log e = 1.5), 350 nm (3.0), and at 260 nm (3.5). The band at 640 nm was assigned to the d-d band of the Cu-O complex in the square planar ligand field. The viscosity of the Cu(II)-PVA aqueous solution diminished sharply with complex formation. The polymer-metal complex probably assumed a tightly packed conformation. A Cu-O stretching band in the polymer complex film appeared at 605 cm [15]. Other metal complexes, such as Fe(III)-PVA, were prepared in a similar way [16]. 

Four possible mechanisms for solid-state extraction (a) adsorption onto a solid substrate (b) absorption into a thin polymer or chemical film coated on a solid substrate (c) metal-ligand complexation in which the ligand is covalently bound to the solid substrate and (d) antibody-antigen binding in which the receptor is covalently bound to the solid substrate. 

A great variety of suitable polymers is accessible by polymerization of vinylic monomers, or by reaction of alcohols or amines with functionalized polymers such as chloromethylat polystyrene or methacryloylchloride. The functionality in the polymer may also a ligand which can bind transition metal complexes. Examples are poly-4-vinylpyridine and triphenylphosphine modified polymers. In all cases of reactively functionalized polymers, the loading with redox active species may also occur after film formation on the electrode surface but it was recognized that such a procedure may lead to inhomogeneous distribution of redox centers in the film... 

A novel polysiloxane, containing the isocyanide group pendent to the backbone, has been synthesized. It is observed to react with the metal vapors of chromium, iron and nickel to afford binary metal complexes of the type M(CN-[P])n, where n = 6, 5, 4 respectively, in which the polymer-attached isocyanide group provides the stabilization for the metal center. The product obtained from the reaction with Fe was found to be photosensitive yielding the Fe2(CN-[P])q species and extensive cross-linking of the polymer. The Cr and Ni products were able to be oxidized on exposure of thin films to the air, or electrochemically in the presence of an electron relay. The availability of different oxidation states for the metals in these new materials gives hope that novel redox-active polymers may be accessible. 

Focusing on reactions using the Fluid Matrix Technique, we have studied the interaction of chromium vapor with 2 at 200 K (13). The resulting film was found to contain metal complexes encapsulated within the polymer in which the isocyanide group adopts a well-defined octahedral arrangement around the chromium center, i.e. a species of type Cr(CN-[P])g. Since characterization of this metal complex within the polymer is not trivial we shall develop the analysis in a little detail. 

Tetra(o-aminophenyl)porphyrin, H-Co-Nl TPP, can for the purpose of electrochemical polymerization be simplistically viewed as four aniline molecules with a common porphyrin substituent, and one expects that their oxidation should form a "poly(aniline)" matrix with embedded porphyrin sites. The pattern of cyclic voltammetric oxidative ECP (1) of this functionalized metal complex is shown in Fig. 2A. The growing current-potential envelope represents accumulation of a polymer film that is electroactive and conducts electrons at the potentials needed to continuously oxidize fresh monomer that diffuses in from the bulk solution. If the film were not fully electroactive at this potential, since the film is a dense membrane barrier that prevents monomer from reaching the electrode, film growth would soon cease and the electrode would become passified. This was the case for the phenolically substituted porphyrin in Fig. 1. 

Following these early solid-state investigations, 1,907 nm EFISHG studies by Tam and co-workers on several complexes [W(CO)5L] (L = py or a 4-substituted py) quote (3 values similar to that of 4-nitroaniline (ca. 10 x 10-30 esu) and sensitive to the nature of the pyridyl substituent.67-69 These results were quickly followed by ZINDO/SCI-SOS calculations on the same series of complexes by Kanis et al.70 the first time that MO theory had been used to describe the quadratic NLO responses of metal complexes. The results of these calculations agree reasonably well with the EFISHG data, and indicate that the modest (3 responses can be traced to relatively small Ap12 values.70 Lacroix et al. obtained low 1,064 nm SHG activities by corona poling films of poly (4-vinylpyridine) and of two other related polymers functionalized with W(CO)5 centers.71... 

Although the exact mechanism of the fluorenone formation is not known, it is believed that the monoalkylated fluorene moieties, present as impurities in poly(dialkylfluorenes), are the sites most sensitive to oxidation. The deprotonation of rather acidic C(9)—H protons by residue on Ni(0) catalyst, routinely used in polymerization or by metal (e.g., calcium) cathode in LED devices form a very reactive anion, which can easily react with oxygen to form peroxides (Scheme 2.26) [293], The latter are unstable species and can decompose to give the fluorenone moiety. It should also be noted that the interaction of low work-function metals with films of conjugated polymers in PLED is a more complex phenomenon and the mechanisms of the quenching of PF luminescence by a calcium cathode was studied by Stoessel et al. [300],... 

While such a film format is not intended for routine use in e.g. soHd phase synthesis, it has proved useful for spectroscopic mechanistic investigation of polymer-supported metal complex catalysts [49] and we, with our collaborators, are employing such films as a component in nanosecond fluorescence sensing devices [50]. 

The polymer CgoPt has also been made by using Pt(l,5-cyclooctadiene)2 [88], Various CjoM polymer films have been prepared by electrochemical reduction of transition metal complexes of the central metal Pd(II), Pt(II), Ir(I), Rh(l), Rh(ll), Rh(lll) and Au(l) [89, 90]. The metal complex in solution is first electrochemicaUy reduced to the zerovalent metal, which then forms polymer films containing M Coo on the electrode. 

A problem especially with oxidation catalysts is that the metals in their highest oxidation state tend to be less strongly associated with a support, so that the reaction conditions can lead to leaching of the metal complex from the support. To overcome this problem, microencapsulation, as an immobilization technique for metal complexes, has been introduced by Kobayashi and coworkers. In the microencapsulation method, the metal complex is not attached by covalent bonding but is physically enveloped by a thin film of a polymer, usually polystyrene. With this technique leaching of the metal can be prevented. In 2002, Lattanzi and Leadbeater reported on the use of microencapsulated VO(acac)2 for the epoxidation of allylic alcohols. In the presence of TBHP as oxidant, it was possible to oxidize a variety of substrates with medium to good yields (55-96%) and diastereomeric ratios (60/40 to >98/2) (equation 42). The catalyst is easily prepared and can be reused several times without significant loss in activity. 

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