Facile Synthesis of Thienopyrroledione-Based π-Conjugated Polymers via Direct Arylation Polycondensation under Aerobic Conditions

Intrinsically Stretchable and Healable Polymer Semiconductors

In recent decades, polymer semiconductors, extensively employed as charge transport layers in devices like organic field-effect transistors (OFETs), have undergone thorough investigation due to their capacity for large-area solution processing, making them promising for mass production. Research efforts have been twofold: enhancing the charge mobilities of polymer semiconductors and augmenting their mechanical properties to meet the demands of flexible devices. Significant progress has been made in both realms, propelling the practical application of polymer semiconductors in flexible electronics. However, integrating excellent semiconducting and mechanical properties into a single polymer still remains a significant challenge. This review intends to introduce the design strategies and discuss the properties of high-charge mobility stretchable conjugated polymers. In addition, another key challenge faced in this cutting-edge field is maintaining stable semiconducting performance during long-term mechanical deformations. Therefore, this review also discusses the development of healable polymer semiconductors as a promising avenue to improve the lifetime of stretchable device. In conclusion, challenges and outline future research perspectives in this interdisciplinary field are highlighted.

Synthesis of Organic Optoelectronic Materials Using Direct C-H Functionalization

Small molecules and polymers with conjugated structures can be used as organic optoelectronic materials. These molecules have conventionally been synthesized by cross-coupling reactions; however, in recent years, direct functionalization of C-H bonds has been used to synthesize organic optoelectronic materials. Representative reactions include direct arylation reactions (C-H/C-X couplings, with X being halogen or pseudo-halogen) and cross-dehydrogenative coupling (C-H/C-H cross-coupling) reactions. Although these reactions are convenient for short-step synthesis, they require regioselectivity in the C-H bonds and suppression of undesired homo-coupling side reactions. This review introduces examples of the synthesis of organic optoelectronic materials using two types of direct C-H functionalization reactions. In addition, we summarize our recent activities in the development of direct C-H functionalization reactions using fluorobenzenes as substrates. This review covers the reaction mechanism and material properties of the resulting products.

Room Temperature Synthesis of a Well-Defined Conjugated Polymer Using Direct Arylation Polymerization (DArP)

While a major improvement to the sustainability of conjugated polymer synthesis, traditional direct arylation polymerization (DArP) still requires high temperatures (typically >100 °C), necessitating a significant energy input requirement. Performing DArP at reduced or ambient temperatures would represent an improvement to the sustainability of the reaction. Here we describe the first report of a well-defined conjugated polymer synthesized by DArP at room temperature. Previous efforts toward room temperature DArP relied on the use of a near-stoichiometric silver reagent, an expensive coinage metal, which makes the reaction less cost-effective and sustainable. Here, room temperature polymerizations of 3,4-ethylenedioxythiophene (EDOT) and 9,9-dioctyl-2,7-diiodofluorene were optimized and provided molar mass (Mn) up to 11 kg/mol PEDOTF, and performing the reaction at the standard ambient temperature of 25 °C provided Mn up to 15 kg/mol. Model studies using other C-H monomers of varying electron density copolymerized with 9,9-dioctyl-2,7-diiodofluorene provided insight into the scope of the room temperature polymerization, suggesting that performing room temperature DArP is highly dependent on the electron richness of the C-H monomer.

Polymers based on thieno[3,4-c]pyrrole-4,6-dione and pyromellitic diimide by CH–CH arylation reaction for high-performance thin-film transistors

Three homopolymers were successfully synthesized by direct CH–CH arylation polymerization of thieno[3,4-c]pyrrole-4,6-dione or pyromellitic diimide derivatives affording highly purified polymers with high molecular weights (43.0–174.7 K). Thieno[3,4-c]pyrrole-4,6-dione and pyromellitic diimide derivatives are considered as electron-withdrawing units. The synthesized homopolymers P1, P2, and P3 showed band gaps in the range of 2.13–2.08 eV, respectively. The electron mobilities of the three homopolymers have been investigated. The thin film transistor for P1 prepared by the eutectic-melt-assisted nanoimprinting method achieved an electron mobility of 2.11 × 10⁻³ cm² s⁻¹ V⁻¹. Based on the obtained results, the synthesized polymers can be used as potential electron acceptors in solar cell applications.

The homopolymers P1, P2 and P3 were successfully synthesized by direct CH–CH arylation polymerization in an eco-friendly one-step coupling reaction. They present n-type properties for potential applications as acceptor polymers.

Synthesis of Conjugated Polymers via Transition Metal Catalysed C-H Bond Activation

Transition metal catalysed C-H bond activation chemistry has emerged as an exciting and promising approach in organic synthesis. This allows us to synthesize a wider range of functional molecules and conjugated polymers in a more convenient and more atom economical way. The formation of C-C bonds in the construction of pi-conjugated systems, particularly for conjugated polymers, has benefited much from the advances in C-H bond activation chemistry. Compared to conventional transition-metal catalysed cross-coupling polymerization such as Suzuki and Stille cross-coupling, pre-functionalization of aromatic monomers, such as halogenation, borylation and stannylation, is no longer required for direct arylation polymerization (DArP), which involve C-H/C-X cross-coupling, and oxidative direct arylation polymerization (Ox-DArP), which involves C-H/C-H cross-coupling protocols driven by the activation of monomers' C(sp² )-H bonds. Furthermore, poly(annulation) via C-H bond activation chemistry leads to the formation of unique pi-conjugated moieties as part of the polymeric backbone. This review thus summarises advances to date in the synthesis of conjugated polymers utilizing transition metal catalysed C-H bond activation chemistry. A variety of conjugated polymers via DArP including poly(thiophene), thieno[3,4-c]pyrrole-4,6-dione)-containing, fluorenyl-containing, benzothiadiazole-containing and diketopyrrolopyrrole-containing copolymers, were summarized. Conjugated polymers obtained through Ox-DArP were outlined and compared. Furthermore, poly(annulation) using transition metal catalysed C-H bond activation chemistry was also reviewed. In the last part of this review, difficulties and perspective to make use of transition metal catalysed C-H activation polymerization to prepare conjugated polymers were discussed and commented.

Conjugated microporous polymers using a copper-catalyzed [4 + 2] cyclobenzannulation reaction: promising materials for iodine and dye adsorption

A new design strategy is disclosed to synthesize conjugated microporous polymers using a Cu-catalyzed [4 + 2] cyclobenzannulation reaction. The polymers reveal BET surface areas up to 794 m² g⁻¹ and promising uptake of iodine and methylene blue.

“In-water” direct arylation polymerization (DArP) under aerobic emulsion conditions

To address the issue of generating large amounts of organic waste from conjugated polymer synthesis, the first direct arylation polymerization (DArP) protocol under emulsion conditions is disclosed with a 10-fold reduction of organic solvent utilized.

Highly Regioselective Direct C-H Arylation: Facile Construction of Symmetrical Dithienophthalimide-Based π-Conjugated Molecules for Optoelectronics

Controllable direct C-H arylation with high regioselectivity is highly desirable yet remains a formidable challenge. Herein, a facile regioselective direct C-H arylation is developed for efficient construction of a variety of symmetrical dithienophthalimide-based π-conjugated molecules. The resulting methodology is applicable to a wide range of substrates, from electron-rich units to electron-deficient units with large steric end groups. Aryl halides have been confirmed to be able to couple with dithienophthalimide (DTI) via direct C-H arylation, showing high regioselectivity. Varying the functional end groups onto the DTI core has been demonstrated to fine tune the emission colors to cover most of the visible spectra. The results suggest a facile strategy towards highly selective direct C-H arylation, opening the prospects towards efficient construction of π-conjugated molecules for various potential optoelectronic applications.

Synthesis of conjugated polymers via cyclopentannulation reaction: promising materials for iodine adsorption

A new class of conjugated polymers is prepared by means of a versatile palladium-catalyzed cyclopentannulation reaction using a series of specially designed diethynyl aryl synthons with the commercially available 9,10-dibromoanthracene DBA monomer.

Thieno[3,4-c]pyrrole-4,6-dione-based conjugated polymers for organic solar cells

Thieno[3,4-c]pyrrole-4,6-dione (TPD) based conjugated polymers as an electron donor, acceptor and single-component for application in organic solar cells in the past ten years have been intensively reviewed in this Feature Article.

Poly(1,4-phenylene vinylene) Derivatives with Ether Substituents to Improve Polymer Solubility for Use in Organic Light-Emitting Diode Devices

New ether-substituted poly(1,4-phenylene vinylene) (PPV) derivatives were synthesized via Horner-Emmons coupling. The structures of the monomers and the resultant oligomers were confirmed by ¹H and ¹³C NMR spectroscopies. The molecular weights of the oligomers were characterized by gel permeation chromatography, giving the number-average and weight-average molecular weights and the corresponding polydispersity indices. Measurements of UV-vis absorption and fluorescence were used to characterize the optical properties of the oligomers. Estimation of the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels and other electrochemical characteristics of the oligomers were investigated by cyclic voltammetry. Dialkyl and dialkoxy PPV oligomers were also prepared and characterized following the same instrumental methods used for the ether-substituted oligomers, providing a known reference system to judge the performance of the new conjugated oligomers. Devices were fabricated to analyze the electroluminescent characteristics of the oligomers in organic light-emitting diodes.

Synthesis of conjugated polymers via direct C–H/C–Cl coupling reactions using a Pd/Cu binary catalytic system

Selective C–H/C–Br coupling and polycondensation with C–H/C–Cl coupling afforded conjugated polymers in a short synthetic step.