Living Suzuki–Miyaura Catalyst-Transfer Polymerization for Precision Synthesis of Length-Controlled Armchair Graphene Nanoribbons and Their Block Copolymers

Abstract

The bottom-up synthesis of graphene nanoribbons (GNRs) offers a promising approach for designing atomically precise GNRs with tuneable photophysical properties, but controlling their length remains a challenge. Herein, we report an efficient synthetic protocol for producing length-controlled armchair GNRs (AGNRs) through living Suzuki–Miyaura catalyst-transfer polymerization (SCTP) using RuPhos–Pd catalyst and mild graphitization methods. Initially, SCTP of a dialkynylphenylene monomer was optimized by modifying boronates and halide moieties on the monomers, affording poly­(2,5-dialkynyl-p-phenylene) (PDAPP) with controlled molecular weight (M n up to 29.8k) and narrow dispersity (Đ = 1.14–1.39) in excellent yield (>85%). Subsequently, we successfully obtained N = 5 AGNRs by employing a mild alkyne benzannulation reaction on the PDAPP precursor and confirmed their length retention by size-exclusion chromatography. In addition, photophysical characterization revealed that a molar absorptivity was directly proportional to the length of the AGNR, while its highest occupied molecular orbital (HOMO) energy level remained constant within the given AGNR length. Furthermore, we prepared, for the very first time, N = 5 AGNR block copolymers with widely used donor or acceptor-conjugated polymers by taking advantage of the living SCTP. Finally, we achieved the lateral extension of AGNRs from N = 5 to 11 by oxidative cyclodehydrogenation in solution and confirmed their chemical structure and low band gap by various spectroscopic analyses.

Low-Pressure Preparative Size-Exclusion Chromatography: from Narrow Disperse Polymer to Monodisperse Oligomer Batches

“…In this work, the recent advances of catalytic C–C cross-coupling polycondensation protocols toward versatile catalyst-transfer variants will be exploited . More precisely, the polymerization of difunctionalized monomers bearing complementary functional groupsdenoted as A/B in the followingenables a chain-growth mechanism that leads to heterotelechelic polymers with narrow dispersity values ( Đ ), tunable degrees of polymerization ( n ) set by the initiation conditions at the α-terminus, ,, as well as capping of the ω-terminus using monofunctionalized reagents. ,, Corroborated by the recent mechanistic insights, the Suzuki-Miyaura catalyst-transfer polymerization (SCTP) was recently extended to a broad variety of electron-rich and electron-deficient monomers, for the preparation of hyperbranched polymer-analogous molecules, to exploit the end-group chemistries in postpolymerization reactions, as well as to prepare controlled nanoribbon precursors, e.g., via commercially available Buchwald-type Pd G3 precatalysts . In essence, the typical SCTP conditions will be slightly adapted to maintain the focus on the complementing separation stage.…”

Cobalt-Catalyzed Cascade C–H Activation/Annulation Polymerizations toward Diversified and Multifunctional Sulfur-Containing Fused Heterocyclic Polymers

“…The most commonly used synthetic methods toward SFH polymers mainly include cross-coupling polymerizations, including Stille, Suzuki, Kumada, Negishi polycouplings, etc., and cyclization polycondensations. As shown in Figure A, the cross-coupling polymerization approach is mature and efficient but generally requires the use of prefunctionalized SFH monomers with suitable reactivity. − The tedious synthesis of prefunctionalized SFH monomers limits the structural diversity of the resulting SFH polymers to a certain extent. In some cases, the cross-coupling polymerizations may suffer from the issues of costly precious-metal-based catalysts, organometallic reagent waste, and toxic byproducts.…”

Highly Efficient Preparation of Length and Width-Controllable Donor–Acceptor Nanoribbons via Polymerization-Induced Crystallization-Driven Self-Assembly of Fully Conjugated Block Copolymers

“…One major barrier to the CDSA of D–A BCP has been the lack of a versatile living polymerization method for their synthesis. To be specific, conventional chain-growth polymerizations of CPs, such as Kumada catalyst-transfer polymerization, were not effective to achieve living polymerization of various acceptor-type monomers, although they are excellent for donor units like thiophene or fluorene. − To solve this issue, our group recently established a universal Suzuki–Miyaura catalyst-transfer polymerization (SCTP) by employing Buchwald-type precatalysts and boronate tuning strategies, thereby significantly expanding the scope and applicability. , As a result, the living polymerization of both donor and acceptor monomers became possible to give even complex microstructures such as alternating or BCPs, − thereby offering the access to key BCPs for the CDSA of D–A nanostructures.…”