Well-defined nanostructures composed of conjugated polymers have attracted significant attention due to their intriguing electronic and optical properties. However, precise control of the size and uniformity of these semiconducting nanostructures is still rare and challenging, despite recent advances in strategies to obtain self-assembled nanostructures with narrow dispersions. Herein, we demonstrate the preparation of fluorescent conjugated block copolymers by one-shot polymerization and rapid formation of nanofibers in a few minutes via light-induced crystallization-driven self-assembly, driven by facile cis-to- trans photoisomerization of its poly( p-phenylenevinylene) blocks. Furthermore, living self-assembly was possible, allowing not only nanofibers with excellent length control and narrow size distribution but also ABA triblock comicelles and gradient comicelles, to be produced by seeded growth. Lastly, the seeded growth could be activated and deactivated repeatedly by switching the light on and off, analogous to light-induced living radical polymerization.
The polymerization of alkoxy-substituted [2.2]-paracyclophane-1,9-dienes via ring-opening metathesis polymerization (ROMP) to obtain soluble poly(pphenylenevinylene)s is a versatile method due to its living nature which enables the possibility of block copolymerization and end group modification. However, detailed studies on the reactivity behavior and the polymerization process of alkoxysubstituted [2.2]paracyclophane-1,9-dienes have not been reported so far. Herein we present a detailed study on the varying tendencies of the four isomers of dimethoxy-(2-ethylhexyloxy)-[2.2]paracyclophane-1,9-diene to undergo ROMP. Therefore, we carried out polymerization combining all individual isomers with five different metathesis catalysts and collected initiation and propagation kinetics for various combinations. Furthermore, we revealed a specific coordination of the monomer repeating unit to the catalyst during the polymerization process and succeeded to polymerize not only the pseudogeminal isomers but also one of the pseudo-ortho isomers.
Block copolymers composed of a MEH−PPV block and a nonconjugated functional block (molecular weights between 5 and 90 kg/mol) were synthesized in a facile one-pot procedure via ROMP. This one-pot procedure permits the synthesis of numerous block copolymers with little effort. Amphiphilic block copolymers were obtained via incorporation of oxanorbornene carrying a PEG side chain as well as via postpolymerization modification of a reactive ester carrying norbornene derivative with methoxypoly-(ethylene glycol)amine. These amphiphilic block copolymers can be self-assembled into micelles exhibiting different sizes (60−95 nm), morphologies (micelles or fused, caterpillar-like micelles), and optical properties depending on the polymer composition and the micellization procedure. Furthermore, the reactive ester carrying block copolymers enabled the introduction of anchor groups which facilitated the preparation of nanocomposites with CdSe/CdZnS core−shell QDs. The obtained composites were studied using time-resolved photoluminescence measurements. The results revealed an increased interaction based on an accelerated decay of the QD emission for composites as compared to the mixture of the QDs with unfunctionalized polymers.
Here we present the first account of conductive polymer/colloidal nanoplatelet hybrids. For this, we developed DEH-PPV-based polymers with two different anchor groups (sulfide and amine) acting as surfactants for CdSe nanoplatelets, which are atomically flat semiconductor nanocrystals. Hybridization of the polymers with the nanoplatelets in the solution phase was observed to cause strong photoluminescence quenching in both materials. Through steady-state photoluminescence and excitation spectrum measurements, photoluminescence quenching was shown to result from dominant exciton dissociation through charge transfer at the polymer/ nanoplatelet interfaces that possess a staggered (i.e., type II) band alignment. Importantly, we found out that sulfide-based anchors enable a stronger emission quenching than amine-based ones, suggesting that the sulfide anchors exhibit more efficient binding to the nanoplatelet surfaces. Also, shorter surfactants were found to be more effective for exciton dissociation as compared to the longer ones. In addition, we show that nanoplatelets are homogeneously distributed in the hybrid films owing to the functional polymers. These nanocomposites can be used as building blocks for hybrid optoelectronic devices, such as solar cells.
Due to its favorable optoelectronic properties and the accessibility via Grignard metathesis (GRIM) polymerization, poly(3-hexylthiophene) (P3HT) is one of the most applied conjugated polymers. The 'living' nature of GRIM polymerization enables the modification of the polymer and the installation of desired properties. In the present study, two versatile approaches for the synthesis of anchor group-modified P3HT have been developed, which enable the functionalization of various inorganic nanoparticles. Depending on the polymerization conditions, mono-and bifunctional ethynyl-terminated P3HT or solely monofunctionalized aldehyde-terminated P3HT was synthesized. Afterwards, the quantitative introduction of amine, mono-and multidentate disulfide and catechol anchor groups was performed by copper-catalyzed 1,3-dipolar cycloaddition or via imine formation reactions. The influence of the polymeric ligand structure on the functionalization of nanoparticles was then investigated for CdSe@ZnS quantum dots and TiO 2 nanorods by transmission electron microscopy (TEM) and infrared (IR) spectroscopy. Keywords: click chemistry, conjugated polymers, P3HT, GRIM, hybrid nanocomposites IntroductionThe design of conjugated polymers with favorable optoelectronic properties has been the subject of research for several decades. Early on, the application of these organic semiconductors in organic solar cells, light-emitting diodes, optical waveguides and lasers has been envisioned and tested.1 Besides ring-opening metathesis polymerization (ROMP) and cyclopolymerization, Grignard metathesis (GRIM) polymerization represents one of the few 'living' polymerization techniques capable of synthesizing conjugated polymers.2 First discovered by McCullough et al. 2 in 1993, GRIM polymerization enables the facile synthesis of conjugated polymers such as poly(3-alkylthiophenes) (P3ATs) with a high degree of regioregularity. 3 In addition, the synthesis of block copolymers and the incorporation of well-defined polymer end groups is permitted.4,5 As a result, P3ATs obtained from GRIM polymerization have been established as hole-transporting organic semiconductors and are among the most applied conjugated polymers. 2,6 For the formation of hybrid optoelectronic devices P3ATs have also been combined with their inorganic analogs, e.g. TiO 2 or CdSe, as this approach enables the utilization of outstanding electron-and hole-transporting materials. While the concept of hybrid solar cells or light-emitting diodes appears to be superior to common organic solar cells, a major task is to enable efficient interaction of polymers and inorganic nanoparticles, avoiding microphase-separation typically occurring for polymer/ nanoparticle blends, as this lowers the overall device performance.6 Consequently and from a chemical aspect, functional end groups facilitating an effective interaction of conjugated polymers with inorganic nanoparticles are desirable for hybrid optoelectronic devices. 7,8 This allows a homogeneous dispersion of inorganic and organic ma...
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