Facile synthesis of fluorene-based π-conjugated polymers via sequential bromination/direct arylation polycondensation

Fluorescence Switchable Conjugated Polymer Microdisk Arrays by Cosolvent Vapor Annealing

Depositing minute light emitters into a regular array is a basic but essential technique in display technology. However, conventional lithographic methodologies involve multistep and energy-consuming processes. Here, we develop a facile method in which organic and polymeric fluorescent dyes spontaneously aggregate to form a patterned microarray. We find that a thin film of fluorescent π-conjugated polymer transforms into micrometer-sized aggregates when exposed to binary organic vapor at ambient temperature. The arrayed microaggregates can be formed over the whole substrate surface when using a quartz substrate that is prepatterned with regular hydrophilic boxes and hydrophobic grids. The resultant microarray is applicable to optical memories and displays when photoswitchable fluorophores are doped into the polymer matrix.

Sustainable Synthesis of a Fluorinated Arylene Conjugated Polymer via Cu-Catalyzed Direct Arylation Polymerization (DArP)

Direct arylation polymerization (DArP) has enabled the more sustainable synthesis of conjugated polymers through the reduction of waste, elimination of toxic and hazardous byproducts, and through the reduction of overall synthetic steps. However, DArP methodologies have almost exclusively relied on the use of noble metal catalysts, such as those with Pd, counter to the efforts toward sustainability. Herein, we report the optimized synthesis of a flourinated arylene conjugated copolymer via DArP using a low-cost, sustainable copper catalyst. Through optimization of the polymerization conditions, we are able to lower the loading of the catalyst from 50 to 5 mol %. As an example, we are able to obtain molecular weights of 16.4 kDa, accompanied by a yield of 54%, with a loading of only 5 mol % for the Cu catalyst. The synthesized polymers were characterized using ¹H and ¹⁹F NMR spectroscopy, showing agreement with those previously prepared with a minimization or exclusion of defects. This work also demonstrates that Cu-catalyzed DArP methodologies can be compatible with substrates that do not possess directing groups, which can help to facilitate C-H functionalization, allowing for a broadening of substrate scope.

From Linear to Foldamer and Assembly: Hierarchical Transformation of a Coplanar Conjugated Polymer into a Microsphere

Despite the coplanar structure, a conjugated alternating copolymer forms amorphous, well-defined microspheres without π-stacked crystalline domains. Here, we gain insights into the mechanism of how the coplanar conjugated polymer forms amorphous microspheres by means of spectroscopic studies on the assembly/disassembly processes. The difference of the spectral profiles of photoabsorption and photoluminescence with varying solvent/nonsolvent composition clarifies that stepwise assembly takes place through the microsphere formation; [1] intrapolymer linear-to-folding transformation upon diffusion of polar nonsolvent and [2] interpolymer assembly of the foldamers upon further addition of the nonsolvent to form microspheres. As shown in various biopolymers such as proteins and DNA, such stepwise folding and assembly behaviors of conjugated polymers from primary to secondary and tertiary structure open a new way to create transformable functional materials.

Facile one-pot access to π-conjugated polymers via sequential bromination/direct arylation polycondensation

The synthesis of π-conjugated polymers starting from unfunctionalized aromatic monomers via sequential bromination/direct arylation polycondensation was investigated.

C-H Arylation in the Synthesis of π-Conjugated Polymers

C-H activation reactions have allowed us to react traditionally chemically inert bonds in molecules to develop new methods for cross-coupling reactions. This type of reactivity can be applied to conjugated polymer materials in an effort to improve existing synthetic difficulties including harsh reaction conditions, multiple monomer functionalization steps, and organometallic reagent waste. In this Viewpoint, we highlight some of the encouraging advances in direct arylation polymerization (DArP) as well as ongoing challenges for future improvement and utility.

Conjugated Polymer Blend Microspheres for Efficient, Long-Range Light Energy Transfer

Highly luminescent π-conjugated polymeric microspheres were fabricated through self-assembly of energy-donating and energy-accepting polymers and their blends. To avoid macroscopic phase separation, the nucleation time and growth rate of each polymer in the solution were properly adjusted. Photoluminescence (PL) studies showed that efficient donor-to-acceptor energy transfer takes place inside the microspheres, revealing that two polymers are well-blended in the microspheres. Focused laser irradiation of a single microsphere excites whispering gallery modes (WGMs), where PL generated inside the sphere is confined and resonates. The wavelengths of the PL lines are finely tuned by changing the blending ratio, accompanying the systematic yellow-to-red color change. Furthermore, when several microspheres are coupled linearly, the confined PL propagates the microspheres through the contact point, and a cascade-like process converts the PL color while maintaining the WGM characteristics. The self-assembly strategy for the formation of polymeric nano- to microstructures with highly miscible polymer blends will be advantageous for optoelectronic and photonic device applications.

Optically induced mode splitting in self-assembled, high quality-factor conjugated polymer microcavities

We investigate the whispering gallery modes (WGMs) of self-assembled single microspheres. They consist of a recently developed highly fluorescent π-conjugated copolymer and exhibit excellent optical properties with Q-factors up to 10⁴. Under continuous laser irradiation, we observe a splitting of the highly degenerate spherical WGMs into a multiplet of lines. Comparison with the calculated spectral response of a weakly distorted sphere shows that the optical excitation induces a change of the optical path length in the microcavity so that it resembles a prolate spheroid. The separation of the lines is given by the ellipticity and the azimuthal mode number. Measurements in various gaseous environments suggest that the distortion is caused by light induced oxidation of the polymer. Our findings show that photooxidation can be a beneficial mechanism for in-situ tuning of optically active polymer structures.

Silica core/conjugated polymer shell particles via seeded Knoevenagel dispersion polymerization – laser action in whispering gallery mode resonators

Here, we present a seeded Knoevenagel dispersion polymerization to generate hybrid particles with a conjugated polymer shell on inorganic silica cores.