Intralayer Anisotropy in Two-Dimensional Conjugated Covalent Organic Frameworks

Two-dimensional (2D) covalent organic frameworks (COFs), as stacked 2D polymers, have emerged as promising semiconductors with tunable structures and functionalities, offering significant potential in optoelectronics. Achieving in-plane anisotropy in their electronic and optical properties is particularly desirable for applications in electronics, thermoelectrics, and photonics but remains a considerable challenge with existing design and synthesis approaches. Here, we present a novel design strategy to introduce intralayer anisotropy in 2D conjugated COFs (2D aniso-c-COFs) using nodes with large in-plane quadrupole moment imbalances and identical linkers. By rationally designing twelve 2D aniso-c-COFs based on benzodithiophene (BDT) nodes, we impose a highly anisotropic electronic structure that results in unprecedented bidirectional charge transport, where electrons and holes preferentially migrate along divergent directions. These COFs exhibit remarkable charge mobilities, reaching up to 1200 cm ² V ^− 1 s ^− 1 for electrons and 200 cm ² V ^− 1 s ^− 1 for holes, as predicted by Boltzmann transport theory. Parallel to electronic anisotropy, these materials show pronounced optical anisotropy, including giant birefringence (|Δ n | > 1.0) and linear dichroism (|Δ k | > 1.3), which are unprecedented in COFs, enabling selective polarization control and tunable optical responses. Guided by these insights, we synthesized a representative 2D aniso-c-COF, TBDT-P-CN, and experimentally demonstrated its high intrinsic charge mobility. These results establish anisotropic 2D conjugated COFs as a unique platform for bidirectional charge transport and polarization-sensitive optoelectronic applications, paving the way for future advancements in organic crystalline materials.