Dimensional evolution of charge mobility and porosity in covalent organic frameworks

Covalent organic frameworks are an emerging class of covalently linked polymers with programmable lattices and well-defined nanopores. Developing covalent organic frameworks with both high porosity and excellent charge transport properties is crucial for widespread applications, including sensing, catalysis, and organic electronics. However, achieving the combination of both features remains challenging due to the lack of overarching structure-property correlations. Here, we report a strategy toward covalent organic frameworks with tunable dimensionality. The concept relies on splicing one-dimensional charge-conducting channels to form extended networks with tailorable substitution patterns. Such dimensional evolution and substitution control enable fine-tuning of electronic band structure, charge mobility, and porosity. According to surface-area characterization, high-frequency terahertz photoconductivity measurements, and theoretical calculations, the transition from one-dimensional to para-linked two-dimensional networks furnishes a substantial increase in surface area and a decrease in local charge mobility. The latter feature is assigned to substitution-induced electronic band flattening. A subtle balance of surface area (947 m2·g-1) and local charge mobility (49 ± 10 cm2·V-1·s-1) is achieved through the rational design of meta-linked analogs with mixed one-dimensional and two-dimensional superior nature. This work provides fundamental insights and new structural knobs for the design of conductive covalent organic frameworks.