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Due to their diverse potential in advanced electronics and energy technologies, electrically conducting metal–organic frameworks (MOFs) are drawing significant attention. Although hexagonal 2D MOFs generally display impressive electrical conductivity because of their dual in-plane (through bonds) and out-of-plane (through π-stacked ligands) charge transport pathways, notable differences between these two orthogonal conduction routes cause anisotropic conductivity and lower bulk conductivity. To address this issue, we have developed the first redox-complementary dual-ligand 2D MOF Cu3(HHTP)(HHTQ), featuring a π-donor hexahydroxytriphenylene (HHTP) ligand and a π-acceptor hexahydroxytricycloquinazoline (HHTQ) ligand located at alternate corners of the hexagons, which form either parallel HHTP and HHTQ stacks (AA stacking) or alternating HHTP/HHTQ stacks (AB stacking) along the c-axis. Regardless of the stacking pattern, Cu3(HHTP)(HHTQ) supports more effective out-of-plane conduction through either separate π-donor and π-acceptor stacks or alternating π-donor/acceptor stacks, while promoting in-plane conduction through the push–pull-like heteroleptic coordination network. As a result, Cu3(HHTP)(HHTQ) exhibits higher bulk conductivity (0.12 S/m at 295 K) than single-ligand MOFs Cu3(HHTP)2 (7.3 × 10–2 S/m) and Cu3(HHTQ)2 (5.9 × 10–4 S/m). This work introduces a new design approach to improve the bulk electrical conductivity of 2D MOFs by supporting charge transport in both in- and out-of-plane directions.
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From an insulating Zn-porphyrin metallacage to electrically conducting inclusion complexes featuring extended π-donor/acceptor stacks
p-Donor/Acceptor charge-transfer (CT) interactions between redox-complementary p-systems often give rise to non-native optical and electronic properties that are beneficial for modern electronics and energy technologies. However, the formation of extended supramolecular p-donor/acceptor stacks capable of long-range charge transport requires ingenious design strategies that can help reinforce otherwise weak p-donor/acceptor noncovalent interactions. Herein, we demonstrate that a large tetragonal prismatic metal–organic cage (MOC28+) having two parallel p-donor tetrakis(4- carboxyphenyl)-Zn-porphyrin (ZnTCPP) faces located B14 Å apart can accommodate up to three redox-complementary planar aromatic guests (either three p-acceptor guests or two p-acceptors surrounding one p-donor guest) between the ZnTCPP faces, forming extended p-donor/acceptor stacks. While empty MOC28+ behaves as an insulator due to the lack of charge delocalization across its large cavity, its inclusion complexes saturated with p-acidic hexaazatriphenylene hexacarbonitrile (HATHCN) and hexacyanotriphenylene (HCTP) displayed noticeably higher electrical conductivity (8.7 10 6 and 1.3 10 6 S m 1, respectively) owing to more facile charge transport through the p-donor/ acceptor stacks composed of the p-acidic guests intercalated between the ZnTCPP faces. Thus, this work demonstrates that tetragonal prismatic metallacages with two parallel electroactive faces can facilitate the creation of extended p-donor/acceptor stacks by encapsulating redox-complementary planar guests, which in turn facilitates through-space charge delocalization, generating non-native electrical conductivity.
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- PAR ID:
- 10630561
- Publisher / Repository:
- Royal Society of Chemistry, UK
- Date Published:
- Journal Name:
- Materials Advances
- ISSN:
- 2633-5409
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1039/d5ma00653h
