Synthesis Of Polyacetylenes With Assembling Functionalities And Their Hybridization With Inorganic Nanostructures

Hybrids based on conjugated polymers and inorganic nanomaterials have attracted much attention among scientists in the areas of solar cells, sensors, display, optical nonlinearity and light-emitting diodes. Polyacetylene is an archetypalÏ€-conjugated polymer and its derivatives bearing appropriate substituents have exhibited a variety of novel properties, such as light emission, nonlinear optical property, chirality amplification and liquid crystallinity. The hybridization of polyacetylenes with inorganic nanostructures and the systematic study on the preparation and properties of the hybrids will be significant both for enriching and developing the fundamental understanding of photoelectronic functional materials, and for fabricating electronic and optical devices based on conjugated polymers.Unfortunately, the immiscibility between polyacetylenes and inorganic materials and the challenge to synthesize the polyacetylenes with self-assembling functionalities on the side chains make the hybridization of polyacetylenes and inorganic materials to be a hard task. In this paper, we took this challenge. Through molecular design, catalyst selection and optimization of polymerization conditions, we successfully synthesized a series of functional polyacetylene derivatives bearing different self-assembling anchor groups such as thiol, amino and pyridyl. Utilizing the strong interactions between these groups and inorganic nanostructures, we prepared several types of hybrids based on polyacetylenes and inorganic nanomaterials, e.g. CdS nanorods, ZnO nanoparticles, layered PbBr₂ perovskite structures and Ag nanoparticles, and studied the derived hybrids' properties such as photoconductivity, conductivity and light emitting properties.We firstly synthesized a thiol-functionalized acetylene monomer, but the monomer cannot be polymerized directly because of the poisoning effect of thiol group on the early transition-metal catalysts. Though [Rh(cod)Cl]₂ can catalyze the polymerizations, the products are insoluble and intractable. Hence, we changed to a modified way and successfully prepared soluble hybrids of poly(phenylacetylene) (PPA) and CdS nanorods by copolymerizations of phenylacetylene with the thiol-functionalized acetylene monomer chemisorbed on the surface of CdS nanorods. The hybrid exhibited excellent stability, solubility and film formability. The interaction between thiol group and CdS nanorods greatly improved the compatibility between the organic and inorganic components. CdS nanorods were uniformly dispersed in the film of the hybrid and the photoinduced charge transfer happened between the n-type inorganic nanostructure and p-type polyacetylenes, which enhanced the photoconductivity of the hybrid.Secondly, through molecular design, catalyst selection and optimization of polymeric conditions, we further tackled the problem of the insolubility of thiol-functionalized Polyacetylene derivatives and synthesized three kinds of new polyacetylenes with the sulfur-containing pendants, which can dissolve in many common organic solvents. The hybrids of these sulfur-containing polyacetylenes and multiwalled carbon nanotubes (MWNTs) showed good solubility in organic solvents. Meanwhile, the wrapping of the polymer chains on MWNTs led to the surface functionalization. By aid of the interaction between sulfur-containing group and Zinc cations, ZnO nanoparticles were assembled onto out-shells of the hybrids and hence new three-component nanohybrids of polymer/MWNTs/ZnO were derived. In the hybrids, all the components retained their pristine electric feature and both CNTs and ZnO nanoparticles preserved their pristine morphological characteristics. The inorganic components attached onto CNTs in a "soft-landing" way instead of direct contacting with CNTs in the traditional chemical or physical vapor deposition method, which may result in the damage to CNTs. The successful fabrication of polymer/MWNTs/CdS nanorods hybrids indicated that in our method, we may prepare the inorganic nanostructures with well-defined shape in advance and then assemble them onto the template of CNTs. It was definite that our method is prior to the hydrothermal and solvothermal methods, in which, the morphology of the inorganic materials is uncontrollable. These results suggested a novel route to the fabrication of multi-component nanostructures.Thirdly, we synthesized a Polyacetylene with pyridyl group, quaternization of which afforded a type of polysalt. The strong electrostatic interactions among the charged pyridyl groups extended the conjugation length and enhanced the thermal stability of the polymer. By adding Ag⁺ into the solution of the polysalt and subsequently exposing to the UV light to in situ decompose the AgI formed in the system, we prepared polymer/Ag nanoparticles hybrid. The size of Ag nanoparticles can be controlled by the amount of Ag⁺ added in the solution and the hybrids showed very excellent storage-stability, which provide a new method to prepare Ag nanoparticles stabilized by polymers. The conductivity of the hybrids was increased with increasing the amount of Ag nanoparticles.A disubstituted Polyacetylene (PA) with phthalimido group was synthesized, hydrolysis and quaternization of which afforded the desired PA ammonium salt. Mixing this polysalt with PbBr₂ readily yielded a highly photoresponsive perovskite hybrid containing an electroactive Polyacetylene. In the hybrid, organic component endows it with solvent miscibility, macroscopic processability, electronic conjugation, and photonic responsiveness, while the inorganic component helps lengthen the electronic conjugation, weaken the chain interaction, supply the exciton energy, enhance the emission efficiency, and accelerate the photobleaching process. Many properties of the hybrid were better than those of its single components, indicating that the complementary and synergic effects of the two building blocks in the hybrid were realized arising from the molecular interactions between them. The two-dimensional fluorescence image pattern was created by a one-step irradiation process without going through a development step, which has technological implications and may find practical applications in such systems as optical display and information storage.Finally, starting from the observation that the nanowires of disubstituted Polyacetylene with phthalimido group showed dramatic deformation under irradiation of electron beams, we investigated this phenomenon for many nanowires and nanotubes derived from linear and hyperbranched, conjugated and non-conjugated polymers, and it was found that all the polymer nanostructures exhibited the similar behavior. Once the nanowires or nanotubes were annealed at the temperature higher than its glass transition temperature before the SEM measurement, the moving phenomenon disappeared. These experimental results indicated that, just like the bulk polymer materials, there will also be some stress left in the polymer nanowires or nanotubes. This is a very important instruction for the people who want to study and use the polymer nanowires or nanotubes. To avoid the disadvantageous effect of these stress to the properties of polymer nanostructures, one must annealed them before use it, just as what we did before use the polymer materials in the macroscopic world.