Owing to their diverse potential applications in advanced electronics and clean energy technologies, electrically conducting metal–organic frameworks (MOFs) have emerged as one of the most coveted functional materials of the twenty-first century. Although 2D hexagonal MOFs often display impressive electrical conductivity due to their simultaneous in-plane (through bonds) and out-of-plane (through π-stacked ligands) charge transport capabilities, large disparities between these two orthogonal conduction pathways cause anisotropic conductivity and dampen the bulk conductivity. To address this issue and boost the bulk conductivity of 2D MOFs, we constructed the first π-intercalated GMOF (iGMOF1) containing built-in alternating π-donor/acceptor stacks made of Cu(II)-coordinated π-donor hexaaminotriphenylene (HATP) ligands and non-coordinatively intercalated π-acceptor hexacyanotriphenylene (HCTP) molecules, which facilitated out-of-plane conduction while the hexagonal Cu₃(HATP)₂ scaffold enabled in-plane conduction (Angew. Chem. Int. Ed. 2023). As a result, iGMOF1 displayed an order of magnitude higher bulk electrical conductivity and much smaller activation energy than Cu₃(HATP)₂ (s = 25 vs. 2 S/m, E_a = 36 vs. 65 meV), demostrating that simultaneous in-plane (through-bond) and out-of-plane (through π-donor/acceptor stacks) charge transport can generate higher electrical conductivity. We subsequently developed the first redox-complementary dual-ligand 2D MOF (CDL-MOF1) Cu₃(HHTP)(HHTQ) composed of a π-donor hexahydroxy-triphenylene (HHTP) ligand and a π-acceptor hexahydroxy-tricycloquinazoline (HHTQ) ligand, which occupied the alternate corners of the hexagonal framework and formed parallel HHTP/HHTP and HHTQ/HHTQ stacks along the c-axis (manuscript submitted). CDL-MOF1 displayed a distinctly higher bulk conductivity (0.12 S/m, 295 K) than its parent single-ligand Cu₃(HHTP)₂ (7.3×10^–2 S/m) and Cu₃(HHTQ)₂(5.9×10^–4 S/m) MOFs, which can be attributed to an improved in-plane charge transport through the push–pull-type heteroleptic coordination network, as well as out-of-plane conduction through the parallel π-donor and π-acceptor stacks that can function as separate electron and hole transport channels. This work presented a novel design strategy that can facilitate both in-plane and out-of-plane charge transport in 2D MOFs and thereby generate improved electrical conductivity.

Jorge Barroso

Appearances