Synthesis, Self‐Assembly, and Applications of Polyferrocenylsilane Block Copolymers

Synthesis and structure of an asymmetrical sila[1]magnesocenophane

The synthesis and structure of an asymmetrical sila[1]magnesocenophane, featuring a cyclopentadienyl and a tetramethylcyclopentadienyl group, are reported. The compound was obtained as a bis(tetrahydrofuran) adduct and exhibits a slipped sandwich structure in the solid state.

Solution Self-Assembly of Coil-Crystalline Diblock Copolypeptoids Bearing Alkyl Side Chains

Polypeptoids, a class of synthetic peptidomimetic polymers, have attracted increasing attention due to their potential for biotechnological applications, such as drug/gene delivery, sensing and molecular recognition. Recent investigations on the solution self-assembly of amphiphilic block copolypeptoids highlighted their capability to form a variety of nanostructures with tailorable morphologies and functionalities. Here, we review our recent findings on the solutions self-assembly of coil-crystalline diblock copolypeptoids bearing alkyl side chains. We highlight the solution self-assembly pathways of these polypeptoid block copolymers and show how molecular packing and crystallization of these building blocks affect the self-assembly behavior, resulting in one-dimensional (1D), two-dimensional (2D) and multidimensional hierarchical polymeric nanostructures in solution.

Polyferrocenylsilane Semicrystalline Polymer Additive for Solution-Processed p-Channel Organic Thin Film Transistors

In this study, we demonstrated for the first time that a metal-containing semicrystalline polymer was used as an additive to mediate the thin film morphology of solution-grown, small-molecule organic semiconductors. By mixing polyferrocenylsilane (PFS) with an extensively-studied organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene), PFS as a semicrystalline polymer independently forms nucleation and crystallization while simultaneously ameliorating diffusivity of the blend system and tuning the surface energies as a result of its partially amorphous property. We discovered that the resultant blend film exhibited a 6-fold reduction in crystal misorientation angle and a 3-fold enlargement in average grain width. Enhanced crystal orientation considerably reduces mobility variation, while minimized defects and trap centers located at grain boundaries lessen the adverse impact on the charge transport. Consequently, bottom-gate, top-contact organic thin film transistors (OTFTs) based on the TIPS pentacene/PFS mixture yielded a 40% increase in performance consistency (represented by the ratio of average mobility to the standard deviation of mobility). The PFS semicrystalline polymer-controlled crystallization can be used to regulate the thin film morphology of other high-performance organic semiconductors and shed light on applications in organic electronic devices.

Electrochemical Characterization and Catalytic Application of Gold-Supported Ferrocene-Containing Diblock Copolymer Thin Films in Ethanol Solution

This paper reports the electrochemical behavior and catalytic property of electrode-supported thin films of polystyrene-block-poly(2-(acryloyloxy)ethyl ferrocenecarboxylate) (PS-b-PAEFc) in an ethanol (EtOH) solution. The electrochemical properties of PS-b-PAEFc films with different PAEFc volume fractions (f_PAEFc = 0.47, 0.30, and 0.17) in 0.1 M ethanolic sodium hexafluorophosphate (NaPF₆) were compared with those in an acetonitrile (MeCN) solution of 0.1 M tetrabutylammonium hexafluorophosphate. Pristine PS-b-PAEFc films did not afford significant faradaic currents in the EtOH solution because EtOH is a nonsolvent for both PS and PAEFc. However, the films could be rendered redox-active in the EtOH solution by applying potentials in the MeCN solution to induce the redox-associated incorporation of the supporting electrolytes into the films. Atomic force microscopy images verified the stability of PAEFc microdomains upon electrochemical measurements in these solutions. Cyclic voltammograms measured in the EtOH solution for PS-b-PAEFc with the larger f_PAEFc were diffusion-controlled regardless of ellipsometric film thickness (23-152 nm) at relatively slow scan rates, in contrast to those in the MeCN solution that were controlled by surface-confined redox species. The electron propagation efficiency in the EtOH solution was significantly lower than that in the MeCN solution because of the poorer swelling of the films, which limited the migration of counterions and the collisional motions of the ferrocene moieties. PS-b-PAEFc films were applied as electrochemically responsive heterogeneous catalysts based on the ferrocenium moieties for Michael addition reaction between methyl vinyl ketone and ethyl 2-oxocyclopentanecarboxylate (E2OC) in 0.1 M NaPF₆/EtOH. The catalytic activities of thin films were similar regardless of f_PAEFc, suggesting that the catalytic reaction took place for the reactants that could penetrate through the film and reach PAEFc microdomains communicable with the underlying electrode. Interestingly, the permeability of PS-b-PAEFc films provided a means to control the reaction selectivity, as suggested by negligible reaction of E2OC with trans-4-phenyl-3-buten-2-one.

Windmill-shaped octanuclear Zn/Ln (LnIII = Dy, Tb, Ho) heterometallic ensembles supported by a tetraferrocene scaffold

Utilizing a new ferrocene-based compartmental ligand, H₄L (1), a series of novel heterometallic complexes [{LZn(μ-OAc)Dy}₄(μ₄-H₂O)] (2), [{LZn(μ-OAc)Tb}₄(μ₄-H₂O)] (3), [{LZn(μ-OAc)Ho}₄(μ₄-H₂O)] (4), [L = Fe[(C₅H₄){-C(Me)[double bond, length as m-dash]N-N[double bond, length as m-dash]C₆H₃-(o-O)(m-O)}]₂] were synthesized and characterized. 2 and 3 crystallize in the monoclinic crystal system in the I2/m space group, whereas 4 crystallizes in the tetragonal crystal system in the I4/m space group. The tetra deprotonated ligand L^4- has two distinct coordination compartments: one pocket (2N, 2O) suitable for the transition metal (3d) ions and another pocket (4O) suitable for lanthanide (4f) metal ions. Additionally, the terminal phenoxo group can be utilized for cluster expansion. In all the complexes, the Zn^II ion is in a perfect square pyramidal (2N, 3O) geometry whereas the lanthanide ion has a coordination number of eight (8O) in a distorted biaugmented trigonal-prism geometry. The electrochemical properties of 2 and 3 along with ligand H₄L (1) were studied by cyclic voltammetry (CV). All the complexes display a similar type of electrochemical behavior viz., one quasi-reversible oxidation typical of a ferrocene/ferrocenium motif. The magnetic properties of all the complexes have also been investigated.

Polyferrocenylsilanes: synthesis, properties, and applications

This comprehensive review covers polyferrocenylsilanes (PFSs), a well-established, readily accessible class of main chain organosilicon metallopolymer. The focus is on the recent advances involving PFS homopolymers and block copolymers and the article covers the synthesis, properties, and applications of these fascinating materials.

Electron Propagation within Redox-Active Microdomains in Thin Films of Ferrocene-Containing Diblock Copolymers

This paper reports the electrochemical behavior of redox-active microdomains in thin films of ferrocene-containing diblock copolymers, polystyrene-block-poly(2-(acryloyloxy)ethyl ferrocenecarboxylate) (PS-b-PAEFc). PS-b-PAEFc with different PAEFc volume fractions (PS154-b-PAEFc51, PS154-b-PAEFc26, and PS154-b-PAEFc12, where the subscripts represent the polymerization degree of each block; f(PAEFc) = 0.47, 0.30, and 0.17, respectively) was synthesized by sequential atom transfer radical polymerization. PS-b-PAEFc films of controlled thicknesses (20-160 nm) were prepared on gold substrates via spin-coating and characterized by ellipsometry. Microdomains were observed via atomic force microscopy on the surfaces of PS154-b-PAEFc51 and PS154-b-PAEFc26 thin films but not on the surfaces of PS154-b-PAEFc12 thin films. Electrochemical behavior of films was assessed by cyclic voltammetry and chronocoulometry in acetonitrile solution. The redox potential of ferrocene moieties was similar (ca. + 0.29 V vs Fc(+)/Fc) regardless of fPAEFc and film thickness. For PS154-b-PAEFc51 and PS154-b-PAEFc26, thicker films afforded larger faradaic peak currents and exhibited diffusion-controlled voltammograms at faster sweep rates. PS154-b-PAEFc26 produced voltammograms less influenced by solvent-induced swelling than PS154-b-PAEFc51, reflecting the improved morphological stability of PAEFc microdomains by redox-inert PS frameworks. In contrast, PS154-b-PAEFc12 films yielded similar faradaic peak currents regardless of film thickness and exhibited voltammograms indicative of surface-confined species. These observations suggest that PS154-b-PAEFc51 and PS154-b-PAEFc26 films contain continuous PAEFc microdomains extending from the electrode to the surface, in contrast to the PS154-b-PAEFc12 films which contain isolated PAEFc microdomains buried within the PS matrix. Electron propagation took place only through PAEFc microdomains that could electrically communicate with the underlying electrode. Apparent diffusion coefficients within PAEFc microdomains were similar (≈ 2 × 10(-11) cm(2)/s) for PS154-b-PAEFc51 and PS154-b-PAEFc26. The relatively low efficiency in electron propagation was attributable to ineffective electron self-exchange reaction within the PAEFc microdomains and/or limited counterion migration through the acetonitrile-swollen microdomains. These results provide guidance in design of redox-active metalloblock copolymers for various applications, which include electrocatalysis, electrochemical mediation in enzyme sensors, and redox-controlled molecular deposition.

Water-soluble and redox-responsive hyperbranched polyether copolymers based on ferrocenyl glycidyl ether

Hyperbranched polymers based on glycidol and ferrocenyl glycidyl ether are prepared, characterized, and their redox behavior in water is studied and quantified with Mößbauer spectroscopy.

Synthesis and self-assembly of poly(ferrocenyldimethylsilane)-block-poly(2-alkyl-2-oxazoline) block copolymers

The synthesis and self-assembly of organometallic poly(ferrocenyldimethylsilane)-block-poly(2-alkyl-2-oxazoline) (PFDMS-b-POx) diblock copolymers of different weight fractions in the bulk and in solution is investigated.

Vinyl ferrocenyl glycidyl ether: an unprotected orthogonal ferrocene monomer for anionic and radical polymerization

Vinyl ferrocenyl glycidyl ether (VfcGE) is the first ferrocene-based, orthogonal monomer for both anionic and radical polymerization to generate polyvalent and redox-active materials.

Controlling aqueous self-assembly mechanisms by hydrophobic interactions

We report an innovative template-assisted synthetic protocol for the selective functionalization of terminal triple bonds in oligophenyleneethynylenes (OPE) by pre-organization in aqueous solution. By this approach, three new OPE-based bolaamphiphiles substituted with hydrophilic poly(2-ethyl-2-oxazoline) (PEtOx) chains of different length have been synthesized. The chain length was observed to strongly influence the aqueous supramolecular polymerization: bolaamphiphiles with longer hydrophilic chains aggregate into spherical nanoparticles in a stepwise fashion, whereas 2D anisotropic platelets are formed cooperatively if shorter PEtOx chains are used. Our results demonstrate that hydrophobic interactions can be strong enough to trigger cooperative effects in aqueous self-assembly processes.

Optical properties of poly(ferrocenylsilane) multilayer thin films

Spectroscopic ellipsometry has been used to investigate the optical properties of poly(ferrocenylsilane) polyion multilayer thin films in the visible and near-infrared range of the spectrum. The thin films were deposited using the layer-by-layer assembly process. Films with thicknesses of up to 55 nm were fabricated stepwise from polyelectrolyte solutions with a controlled ionic strength. These films allow an accurate characterization of the optical properties of poly(ferrocenylsilane) polyion layers. We show that the complex refractive index can be described by a simple Cauchy model. Refractive index values vary over the spectral range from 1.53 (near-infrared) to 1.8 (ultraviolet).

Nanostructured magnetic thin films from organometallic block copolymers: pyrolysis of self-assembled polystyrene-block-poly(ferrocenylethylmethylsilane)

The pyrolysis of cylinder-forming samples of the diblock copolymer polystyrene-block-poly(ferrocenylethylmethylsilane) (PS-b-PFEMS) in bulk and in thin films has confirmed that these materials are useful for the generation of semi-ordered arrays of C/SiC ceramics containing Fe nanoparticles which are derived from the organometallic domains. In many cases, the ceramic mass yields were predictable and produced ceramics bearing a monomodal distribution of iron nanoparticles due to the nanoscaled structure of the preceramic PFEMS domains. The pyrolysis of thin films stabilized by cross-linking the PS domains with UV light demonstrated high areal yields, improved shape retention, and the presence of cylinder-centered magnetic nanoparticles.