Highly Conductive 2D Covalent–Organic Framework Films

Covalent–organic frameworks (COFs) have been widely used in electronics, catalysis, sensing, adsorption, and water purifications for their high crystallinity, porosity, and tunable functionality. However, the practical applications have been limited due to low intrinsic conductivity. Recent studies show that conjugated 2D COFs have the potential to achieve high conductivity and that the rational design of linkers and metal-containing macrocycles and synthesis optimization is important.^[1] Regarding this, our report will demonstrate a bottom-up synthesis of copper-coordinated-fluorinated-phthalocyanine (CuPc) and 2,3,6,7-tetrahydroxy-9,10-anthraquinone-based COF (CuPc-AQ-COF) films, achieving high conductivity levels.^[2] These films demonstrate an electrical conductivity of 1.53 × 10³ S m⁻¹ and a Hall mobility of 6.02 × 10² cm² V⁻¹ s⁻¹ at room temperature, rivaling that of metals. This remarkable performance is attributed to the molecular design that incorporates both 18π electron metal-containing CuPc and a quinone-based linker, and the significantly improved crystallinity of the films prepared via the vapor-assisted method, which all facilitate charge transport within the COFs. Density functional theory analysis further proves the intralayer donor–acceptor system and further reveals that this system has the smallest band gap between the LUMOs of CuPc center and quinone linkages compared to other published similar COFs structures.^[3][4] We also fabricated a field-effect transistor (FET) device with COF films exhibiting bipolar behavior, a low threshold voltage, and a high <i>I</i>_on/<i>I</i>_off. The results demonstrate the potential of the films in electronic applications. Our findings provide valuable insights into the design and fabrication of high-performance COF films. These stable, porous, and crystalline organic networks with metallic conductivity can realize advanced electronic devices, catalysis, and energy storage systems.<br/>Reference:<br/>[1] Y. Yuan, K.-T. Bang, R. Wang, Y. Kim*, <i>Adv. Mater.</i> 2023, 35, 2210952.<br/>[2] R. Wang, H. Lyu, G. S. H. Poon Ho, H. Chen, Y. Yuan, K.-T. Bang, Y. Kim*, <i>Small</i> 2023, 2306634.<br/>[3] Z. Meng, R. M. Stolz, K. A. Mirica*, <i>J. Am. Chem. Soc. </i><b>2019</b>, <i>141</i>, 11929.<br/>[4] C. Yang, K. Jiang, Q. Zheng, X. Li, H. Mao, W. Zhong, C. Chen, B. Sun, H. Zheng, X. Zhuang, J. A. Reimer, Y. Liu, J. Zhang*, <i>J. Am. Chem. Soc. </i><b>2021</b>, <i>143</i>, 17701.