Design of polyethers,thioethers, and amines with pendent iron moieties

Soluble organoiron polyethers, thioethers, and amines were synthesized via nucleophilic aromatic substitution reactions. The synthesis of these classes of organometallic polymers involved either the reaction of cyclopentadienyliron complexes of dichloroarenes with various oxygen and sulfur dinucleophiles or the reaction of ether‐ or amine‐containing diiron complexes with dithiols. Polymerization reactions with the diiron complexes gave rise to organoiron polymers with alternating ether/thioether or amine/thioether bridges. Removal of the iron moieties from the backbone of these polymers allowed for the production of the corresponding organic materials. Furthermore, the organometallic polymers had much higher solubilities than their organic analogues. Thermogravimetric analysis of the organoiron polymers indicated that the polymers lost their metallic moieties at approximately 200 °C, whereas degradation of the polymer backbones occurred around 500 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1216–1231, 2001     

Synthesis of iron-containing polymers with azo dyes in the backbones or side chains

The synthesis of cationic cyclopentadienyliron-containing polymers with pendent azobenzene chromophores was accomplished via metal-mediated nucleophilic aromatic substitution reactions. All of the desired polymers were isolated as vibrantly coloured materials and displayed excellent solubility in polar aprotic solvents. Cationic and neutral cyclopentadienyliron polymers incorporating azo dyes in the backbone were also prepared. Reactions of azo dyes with dichlorobenzene complexes allowed for the isolation of cationic cyclopentdienyliron (CpFe₊) complexes with azo dye chromophores. These complexes were then reacted with 1,1′-ferrocenedicarbonyl chloride to produce the trimetallic monomers with terminal chloro groups. These monomers contained two pendent CpFe₊ cations and a neutral iron moiety in the backbone. Nucleophilic substitution reactions of these monomers with oxygen and sulfur containing dinucleophiles gave rise to a new class of polymeric materials. The pendent CpFe₊ moieties could also be cleaved from the polymer backbones using photolysis to afford novel ferrocene based polymers. The UV-vis spectra of the organoiron monomers and polymers display similar wavelength maxima however incorporating azobenzene chromophores with electron-withdrawing substituent into the polymer chains resulted in bathochromic shifts of the λ_max values.     

New comb-like polymers: Synthesis,structures and reactivity

Comb-like polymers have been widely investigated mainly to correlate their structures with the thermal behaviour. Our interests are directed on the synthesis of new types of comb-like polymers bearing reactive groups in the side chains, main chain or as end groups. One part of the investigations deals with the behaviour of photosensible polymers containing azobenzene, cinnamic acid and mesoionic moieties. The use of enzymes as catalysts for the synthesis of new methacrylic derivatives and for the modification of polymers illustrates a fascinating contribution to polymer chemistry. The classical Diels-Alder addition was also used for the synthesis and modification of polymers. Finally, the construction of polymers containing rotaxanes in the side chains is presented.     

Optical,electrical, and thermochromic properties of polyazothiophene Langmuir–Blodgett films

The conductivity and luminescence of conjugated polymers may be combined with the photoisomerization capability of azobenzene materials to achieve unique properties for a variety of applications, particularly if conjugated polymers with azobenzene side chains are processed as nanostructured films. In this study, we report on Langmuir–Blodgett (LB) films of a polythiophene-bearing azobenzene moieties, which displayed photoluminescence, thermochromism, electroactivity, and photoinduced birefringence. The latter three properties were enhanced in the LB films, as compared to spin-coated films of the polyazothiophene, and this has been attributed to differences in film morphology that could be probed with atomic force microscopy.     

Synthesis of sulfone-containing monomers and polymers using cationic cyclopentadienyliron complexes

The synthesis of sulfone-containing monomers with pendent cationic cyclopentadienyliron (CpFe⁺) moieties has been accomplished via nucleophilic aromatic substitution of dichloroarene complexes with a number aliphatic dithiols. These complexes were further oxidized using m-CPBA to give the sulfone-based monomers. Polymerization of the sulfone-based monomers with O-containing nucleophiles produced the sulfone-based polymers. Direct nucleophilic aromatic substitution of dichloroarene complexes with dinucleophiles allowed for the formation of organoiron sulfide-based polymers. Oxidation of these polymers led to the formation of sulfone polymers with the pendent iron moieties. The organometallic monomers and polymers were found to be more soluble in polar solvents in comparison to their organic analogues.     

Polyethers and thioethers incorporating neutral and cationic organoiron complexes

The synthesis of linear and star-shaped oligomers containing cationic and neutral organoiron groups in their structures was achieved by reaction of cationic arene complexes of cyclopentadienyliron containing terminal hydroxyl groups with 1,1′-ferrocenedicarbonyl chloride or ferrocene carboxylic acid. The use of chloroarene complexes allowed for the formation of triiron complexes that were subsequently polymerized via nucleophilic aromatic substitution with various oxygen- and sulfur-based dinucleophiles. The corresponding polyethers and thioethers were isolated in good yields and these materials exhibited excellent solubilities in polar organic solvents. Cyclic voltammetric investigations revealed that the cationic iron centers pendent to the polymer backbones underwent reversible reduction steps, while the neutral iron centers within the polymer backbones underwent reversible oxidation steps. Photolysis of these polymers resulted in the removal of the cationic cyclopentadienyliron moieties pendent to the polymer backbones. Thermogravimetric analysis (TGA) revealed that the cationic iron complexes were cleaved from the polymers at approximately 210 °C. Differentials scanning calorimetry (DSC) revealed that the glass transition temperatures of the cationic polymers occurred at higher temperatures than their neutral analogs.     

PAMAM-containing semiconducting polymers: Effect of dendritic side chains on optoelectronic and solid-state properties

Dendronized polymers are a particularly interesting platform for the preparation of advanced semiconductors given their high degree of functionalization, monodispersity, and bulkiness. Despite advantageous features, the incorporation of dendritic moieties in semiconducting polymers is still relatively underexplored, and the impact on the optoelectronic, thermomechanical, and solid-state properties are difficult to predict. This work focuses on the incorporation of polyamidoamine (PAMAM) dendritic side chains to semicrystalline polymers based on diketopyrrolopyrrole. Using a versatile synthetic strategy based on the azide-alkyne Huisgen 1,3-dipolar cycloaddition, dendronized semiconducting polymers were prepared and the effect of the dendritic side chains on different properties were carefully characterized using different techniques. The dendritic side chains were found to reduce aggregation and crystallinity of the polymers in thin films. PAMAM-containing semiconducting polymers were also shown to have good charge transport properties in organic field-effect transistors, within the same order of magnitude to that of diketopyrrolopyrrole-based polymers bearing branched alkyl chains. This new design approach is particularly interesting to develop advanced semiconducting polymers given its synthetic versatility and the structural diversity of the dendronized moieties. Furthermore, the utilization of dendritic moieties in semiconducting polymers is a promising approach to fine-tune the thermomechanical properties toward semiconducting polymers for next-generation organic electronics.     

Poly(L-lysine) containing azobenzene units in the side chains: influence of the degree of substitution on liquid crystalline structure and thermotropic behaviour

The structure of poly(L-lysine)s containing between 20% and 100% of azobenzene units in the side chains has been studied by X-ray diffraction, between room temperature and 250 C. Except for samples having very low contents of azobenzene, the polymers are found to exhibit mesomorphic structures of the smectic A1 type deriving from the beta -structure of polypeptides. For polymers in which all lysine residues were substituted, the polypeptide main chains are arranged in layers corresponding to the sheets of a polypeptide 'antiparallel' beta -structure, and the side chains are perpendicular to the smectic layers. For polymers containing both substituted and free lysine side chains, each smectic layer results from the superposition of two layers: one layer contains the free lysine side chains; the other contains the azobenzenemodified lysine side chains and the polypeptide main chains that are arranged in 'antiparallel' beta -structures. All polymers exhibit only one smectic A mesophase as a function of temperature. The thickness of the smectic layers increases with increasing temperature until a thickness is reached that corresponds to the maximum interaction between the azobenzene mesogens in their trans -configuration.     

Photo-induced bending behaviour of side-on linear liquid crystal polymers with high molecular weight

ABSTRACT

Two photoresponsive side-on linear liquid crystal polymers (SLLCPs) with different spacer lengths have been synthesised through facile ring-opening metathesis polymerisation (ROMP). For the first time, high molecular weight SLLCPs with polynorbornene backbone and azobenzene side chains are obtained and processed into films by the melt shear-induced orientation method. These SLLCP films exhibit fast and large photo-induced bending behaviour, showing bend degree up to 72° in 3 s upon UV irradiation at ambient temperature. The shape of these films remains unchanged under visible light, demonstrating good shape stability against sunlight. Moreover, owing to their linear structure, the SLLCP films are recyclable through traditional melting or solution methods. Possessing these features, these SLLCP films show application prospects in the fields of light-controllable flexible actuators.     

Gap-mode SERS studies of azobenzene-containing self-assembled monolayers on Au(1 1 1)

Self-assembled monolayers of azobenzene-containing thiols on smooth Au(1 1 1) surfaces were studied by gap-mode surface-enhanced Raman spectroscopy (gap-mode SERS). By adsorption of colloidal Au nanoparticles on top of the organic adlayer highly reproducible spectra with strongly enhanced intensities are obtained. The observed bands indicate a trans conformation of the azobenzene moieties and are in agreement with structural data for the molecular layer. A characteristic dependency on the terminal and the spacer groups of the molecules is found. Samples prepared during illumination with UV light show pronounced spectral differences that can be attributed to azobenzene in cis conformation.     

Liquid crystalline homopolyesters having main chain calamitic mesogens and one or two side chain azobenzene moieties in the repeat units

Combined semi-rigid homopolyesters, containing both main chain calamitic mesogens and one or two side chain azobenzene units separated by aliphatic (hexamethylene, octamethylene and decamethylene) chains in the polymer repeat units, were prepared and their liquid crystalline properties characterized. Polyesters having two side chain azobenzene units and a main chain biphenyl moiety showed a higher ordered smectic B or smectic F phase, whereas the other polymers containing a main chain 2,5-diphenyl-1,3,4-thiadiazole unit and one or two side chain methoxyazobenzene units formed a smectic C phase despite the presence of different mesogens in the main and side chains. This is probably due to the compact molecular chain-packing and intra- and intermolecular interactions between the polymer backbones and the two azobenzene units.     

Discrimination of structural order and chromophore aggregation as factors effecting the photo-reorientation of azobenzene in copolyglutamate LB films

Photo-reorientation experiments have been performed on LB films of polyglutamates with azobenzene side chains and copolyglutamates with azobenzene moieties and non-photochromic mesogens as side chains. Incorporation of the non-photochromic phenylbenzoate and methyl-substituted biphenyl side chains prevents aggregation of the chromophores, but does not change the LB film structure. Photo-reorientation upon irradiation with polarized light is suppressed by the side-chain structure in the LB film, independent of chromophore aggregation. This structure is disrupted if the amount of side chains which can be photo-isomerized exceeds a critical number. After the structure has been disrupted, photo-reorientation is possible. Not only the chromophores, but also the non-photochromic side chains are reoriented in a cooperative manner.     

Design of Organoiron Macromolecules Based on Upper Rim Functionalized Calix[4]arenes

The versatility of cationic cyclopentadienyliron complexes is demonstrated for the generation of calix[4]arene‐based dendrimers and polymers. Dendrimers were prepared from a branched organoiron calix[4]arene through subsequent reactions of azo dyes and organoiron complexes. The resulting azo dye‐containing metallocalix[4]arenes were soluble in polar organic solvents and displayed λ_max ranging between 430 and 456 nm. Upon addition of various acids, the λ_max shifted to higher wavelengths (513–535 nm). In the solid state and in solution, the azo dye‐containing metallocalix[4]arenes reversibly changed colour in the presence of acid and base, indicating their potential use as acid sensors. Cyclic voltammetric studies showed that the iron centres of the metallocalix[4]arenes were reversibly reduced at E_1/2 = −1.49 V. When non‐branching organoiron‐based calix[4]arene were reacted with dithiols, polymers containing calix[4]arenes either in their side chains or main chains were obtained. The polymers possessed weight average molecular weights between 35 000 and 53 000. The polymers were determined to be thermally stable with backbone decomposition occurring above 500 °C.

     

Polymer-DNA hybrids as electrochemical probes for the detection of DNA

The syntheses of several norbornene block copolymers containing oligonucleotide and ferrocenyl side chains and their use in the electrochemical detection of DNA are described. Two kinds of DNA-containing block copolymers with either ferrocenyl or dibromoferrocenyl groups were prepared via ring-opening metathesis polymerization (ROMP). Based on these two distinct ferrocene derivatives, a triblock copolymer labeling strategy was developed. With this strategy, the identity of DNA target can be determined by the E1/2s of the ferrocenyl moieties and the ratio of peak currents. These polymers exhibit predictable and tailorable electrochemical properties, high DNA duplex stability, and unusually sharp melting transitions, which are highly desirable characteristics for DNA detection applications. Significantly, single-base mismatches could be easily detected using two distinct block copolymers as dual-channel detection probes in an electrochemical DNA detection format.     

Gel formation and photoactive properties of azobenzene-containing polymer in liquid crystal mixture

For the first time, a photochromic azobenzene-containing liquid crystalline (LC) acrylic polymer was used for gelation of low-molar-mass nematic mixture (LMNM). Dissolution of LC polymer in amount of only 2.5 wt.% in LMNM at 120°C (isotropic state) followed by cooling down results in formation of the solid-like photochromic LC gel. Gelation is associated with a phase separation and formation of microsized LC polymer domains, which form a physical “network” containing encapsulated nematic host. Textural changes of mixture during gel formation were analyzed, and absorbance spectra were measured. A special attention was paid to the kinetic study of photoinduced E-Z and Z-E isomerization of azobenzene side groups of polymer in gel. It was shown that ultraviolet (UV)-irradiation and E-Z isomerization processes are accompanied by disruption of H-aggregates of azobenzene moieties and partial dissolution of polymer.     

Organoiron polynorbornenes with pendent arylazo and hetarylazo dye moieties

Organoiron polynorbornene containing arylazo or hetarylazo dye chromophores has been prepared via ring opening metathesis polymerization using Grubbs' catalyst. The obtained polymers were isolated as brightly colored materials and displayed good solubility in polar organic solvents. The colors of these polymers were affected by the nature of the incorporated azo chromophores. Thermogravimetric analysis of these materials showed that the cleavage of the cyclopentadienyliron (CpFe⁺) moieties was between 225 and 231 °C, while the degradation of the polymer backbones occurred between 400 and 450 °C. UV-vis studies in DMF showed that the organoiron polymers containing arylazo dyes exhibit wavelength maxima around 425 nm. However, the replacement of these arylazo moieties with hetarylazo dyes displayed substantial bathochromic shifts in the λ_max values (≈ 511 nm).     

Waveguide spectroscopic characterization of 3D anisotropies in conventionally photooriented and annealed films of liquid crystalline and amorphous azobenzene polymers

Films of azobenzene-containing polymers were photooriented in the glassy state in such a way that the azobenzene side groups were oriented preferably perpendicular to the electric field vector. In the case of liquid crystalline polymers ,the photoinduced anisotropies generated in the glassy state were modified by thermotropic self-organization due to annealing above T(g). The conventional photoorientation process results in an oblate order. The changes in photoinduced anisotropies brought about by annealing in the liquid crystalline phase were investigated quantitatively for the first time by us for different polymer compositions and experimental conditions. Different biaxial and homeotropic orders result for liquid crystalline polymers, depending on the experimental conditions. Different polymer structures are compared and the influence of the interfaces is investigated. Orientational gradients can be induced by irradiation or annealing and are for the first time determined by the WKB (Wentzel-Kramers-Brillouin) method.     

Synthesis and photophysical properties of polyphenylquinoxalines with thiophene and benzothiophene units in side chains

New bis(α-diketones) with thiophene and benzothiophene moieties were synthesized. A series of new polyphenylquinoxalines containing these moieties in side chains was prepared via polycondensation of these diketones with different aromatic tetramines. The polymers are soluble in a variety of organic solvents, and their solutions form transparent films having a tensile strength of σ = 80–100 MPa and an elongation at break of ? = 5–12%. The polymers exhibit fluorescence in solution in trifluoroacetic acid and in films with a maximum at 430–570 and 460–480 nm. The 10% mass loss temperature in air ranges within 440–490°C.     

Ceiling Degree of Polymerization for Brush Polymers Prepared via ROMP of Poly(tert-Butyl Acrylate) Macromonomers

Controlled preparation of brush polymers is important in the design of functional materials. In this study, poly(tert-butyl acrylate) macromonomers functionalized with norbornenyl end group(NB-PtBA) were synthesized via atom transfer radical polymerization in three different molecular weights, 2000(NB-PtBA-2k), 3000(NB-PtBA-3k), and 8000(NB-PtBA-8k). Additionally, brush polymers with PtBA as side chains were synthesized via ring-opening metathesis polymerization(ROMP). Kinetic studies on ROMP of NB-PtBA showed that there was a ceiling degree of polymerization(CDP) for the brush polymers, beyond which the polymerization of NB-PtBA was out of control. For brush polymers of P[NB-PtBA-2k] and P[NB-PtBA-3k], CDPs were estimated to be ca. 400, but the value of P[NB-PtBA-8k] was ca. 100. Therefore, the controlled ROMP of brush polymers was critical at the CDP limit with increased macromonomer molecular weight.     

Photoresponsive self-assembly and self-organization of hydrogen-bonded supramolecular tapes

Self-assembling building blocks that are readily functionalizable and capable of achieving programmed hierarchical organization have enabled us to create various functional nanomaterials. We have previously demonstrated that N,N'-disubstituted 4,6-diaminopyrimidin-2(1 H)-one (DAP), a guanine-cytosine hybridized molecule, is a versatile building block for the creation of tapelike supramolecular polymer species in solution. In the current study, DAP was functionalized with azobenzene side chains. 1H NMR, UV/Vis, and dynamic light scattering studies confirmed the presence of nanometer-scale tapelike supramolecular polymers in alkane solvents at micromolar regimes. At higher concentrations (millimolar regimes), the supramolecular polymers hierarchically organized into lamellar superstructures to form organogels, as shown by X-ray diffraction and polarized optical microscopy. Remarkably, the azobenzene side chains are photoisomerizable even in the supramolecular polymers, owing to their loosely packed state supported by the rigid hydrogen-bonded scaffold, enabling us to establish photocontrollable supramolecular polymerization and higher order organization of the tapelike supramolecular polymers into lamellar superstructures.