Discovery of Organic Optoelectronic Materials Powered by Oxidative Ar–H/Ar–H Coupling

Abstract

Efficient and streamlined synthetic methods that facilitate the rapid build-up of structurally diverse π-conjugated systems are of paramount importance in the quest for organic optoelectronic materials. Among these methods, transition-metalcatalyzed oxidative Ar−H/Ar−H coupling reactions between two (hetero)arenes have emerged as a concise and effective approach for generating a wide array of bi(hetero)aryl and fused heteroaryl structures. This innovative approach bypasses challenges associated with substrate pre-activation processes, thereby allowing for the creation of frameworks that were previously beyond reach using conventional Ar−X/Ar−M coupling reactions. These inherent advantages have ushered in new design patterns for organic optoelectronic molecules that deviate from traditional methods. This ground-breaking approach enables the transcendence of the limitations of repetitive material structures, ultimately leading to the discovery of novel high-performance materials. In this Perspective, we provide an overview of recent advances in the development of organic optoelectronic materials through the utilization of transition-metal-catalyzed oxidative Ar−H/Ar−H coupling reactions. We introduce several notable synthetic strategies in this domain, covering both directed and non-directed oxidative Ar−H/Ar−H coupling strategies, dual chelation-assisted strategy and directed ortho-C−H arylation/cyclization strategy. Additionally, we shed light on the role of oxidative Ar−H/Ar−H coupling reactions in the advancement of high-performance organic optoelectronic materials. Finally, we discuss the current limitations of existing protocols and offer insights into the future prospects for this field.

C–H/C–H Oxidative Direct Arylation Polycondensation to Isoindigo-Based n-Type Conjugated Polymers

“…C–H/C–H oxidative direct arylation polycondensation (Oxi-DArP) via the direct activation of C–H bonds in (hetero)­arenes is the most straightforward and eco-friendly approach for the synthesis of CPs to date because no prefunctionalization or preactivation of monomers is necessary. − Some CPs have been successfully synthesized via Oxi-DArP. For instance, 2,2′-bithiazole-containing CPs have been synthesized by You and Kanbara via Pd- and Cu-catalyzed Oxi-DArP, respectively. , Nakamura et al synthesized triarylamine/bithiophene copolymers through Fe-catalyzed Oxi-DArP, which was used as hole transport materials for the fabrication of efficient perovskite solar cells. , Compared with C–Br/C–H DArP, Oxi-DArP is more straightforward since no prefunctionalized C–Br monomer is necessary. , However, the progress of Oxi-DArP has trailed much behind DArP because only a limited number of (hetero)­arenes can undergo transition-metal-catalyzed oxidative C–H/C–H coupling efficiently to ensure the formation of high molecular weight products. There is also a lack of a design strategy to C–H monomers toward high-mobility CPs via Oxi-DArP.…”

Synthetic progress of organic thermally activated delayed fluorescence emitters via C–H activation and functionalization

“…Thermally activated delayed fluorescence (TADF) emitters have emerged as highly appealing and versatile luminescent materials, garnering considerable interest from researchers across diverse disciplines such as electronics, chemistry, materials science, physics, and biology over the last decade. 1–7 Diverging from conventional fluorescent materials, these distinctive emitters typically manifest an active reverse intersystem crossing (RISC) process. This process involves an endothermic up-conversion from the excited triplet (T 1 ) state to the excited singlet (S 1 ) state, succeeded by radiative decay from S 1 to the ground (S 0 ) state, resulting in delayed fluorescence (DF).…”

“…Since TADF was firstly observed in Eosin Y, it is also referred to as E-type delayed fluorescence (E-type DF) to distinguish it from delayed fluorescence originating from triplet–triplet annihilation (TTA). Following this groundbreaking discovery, TADF compounds and mechanisms began to attract increasing attention, resulting in significant progress across various classes of materials (Scheme 1), including organic dyes, 8 metalloporphyrins, 9 metal complexes, 10 fullerenes, 11 donor–acceptor (D–A) type molecules, 1–7 and multiple resonance frameworks. 12…”

“…13 To enhance k RISC for ideal TADF emission, a practical strategy involves narrowing Δ E ST , favoring the up-conversion process from the low-energy T 1 state to the high-energy S 1 state. 1–7 Generally, Δ E ST is the energy difference between the S 1 ( E S , the energy level of the S 1 state) and T 1 ( E T , the energy level of the T 1 state) states, which can be defined as E S = E + K + J , E T = E + K − J , Δ E ST = E S − E T = 2 J . Here, E is the orbital energy, K is the electron repulsion energy, and J is the exchange energy.…”

“…Here, E is the orbital energy, K is the electron repulsion energy, and J is the exchange energy. 1 According to this, minimizing Δ E ST entails reducing the exchange energy J . As predicted by quantum theory, J is related to the overlap of the spatial wave function of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels in organic molecules.…”