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1. Electrically Conducting Redox‐Complementary Dual‐Ligand 2D Graphitic MOF with Orthogonal Charge Transport Pathways

   https://doi.org/10.1002/aelm.202500319  

   Zhang, Shiyu; Zhang, Weikang; Yadav, Ashok; Ansari, Mohd_A H; Cromer, Jonathan L; Barroso, Jorge; McCarver, Gavin A; Zhou, Wei; Saha, Sourav (August 2025, Advanced Electronic Materials)

   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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2. Strategies to Improve Electrical and Ionic Conductivities of Metal–Organic Frameworks

   https://doi.org/10.1080/02603594.2019.1704738  

   Gordillo, Monica A.; Saha, Sourav (January 2020, Comments on Inorganic Chemistry)

   Owing to their highly ordered crystalline structures and ease of introducing different electroactive meta ions and ligands, metal–organic frameworks (MOFs) have emerged as promising electrical and ion conducting materials. In this minireview, we highlighted recent advances in guest-induced electronic and ionic conductivity of MOFs, which are otherwise insulators or poor conductors. Examples of conductivity enhancement upon guest-induced framework oxidation or reduction, π-donor/acceptor stack formation, crosslinking of coordinatively unsaturated nodes, and binding of mobile Li+ and Mg2+ with the MOFs are discussed. 

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3. Effects of intervalence charge transfer interaction between π-stacked mixed valent tetrathiafulvalene ligands on the electrical conductivity of 3D metal–organic frameworks

   https://doi.org/10.1039/d1sc04338b  

   Zhang, Shiyu; Panda, Dillip K.; Yadav, Ashok; Zhou, Wei; Saha, Sourav (October 2021, Chemical Science)

   null (Ed.)

   Achieving a molecular-level understanding of how the structures and compositions of metal–organic frameworks (MOFs) influence their charge carrier concentration and charge transport mechanism—the two key parameters of electrical conductivity—is essential for the successful development of electrically conducting MOFs, which have recently emerged as one of the most coveted functional materials due to their diverse potential applications in advanced electronics and energy technologies. Herein, we have constructed four new alkali metal (Na, K, Rb, and Cs) frameworks based on an electron-rich tetrathiafulvalene tetracarboxylate (TTFTC) ligand, which formed continuous π-stacks, albeit with different π–π-stacking and S⋯S distances ( d π–π and d S⋯S ). These MOFs also contained different amounts of aerobically oxidized TTFTC˙ + radical cations that were quantified by electron spin resonance (ESR) spectroscopy. Density functional theory calculations and diffuse reflectance spectroscopy demonstrated that depending on the π–π-interaction and TTFTC˙ + population, these MOFs enjoyed varying degrees of TTFTC/TTFTC˙ + intervalence charge transfer (IVCT) interactions, which commensurately affected their electronic and optical band gaps and electrical conductivity. Having the shortest d π–π (3.39 Å) and the largest initial TTFTC˙ + population (∼23%), the oxidized Na-MOF 1-ox displayed the narrowest band gap (1.33 eV) and the highest room temperature electrical conductivity (3.6 × 10 −5 S cm −1 ), whereas owing to its longest d π–π (3.68 Å) and a negligible TTFTC˙ + population, neutral Cs-MOF 4 exhibited the widest band gap (2.15 eV) and the lowest electrical conductivity (1.8 × 10 −7 S cm −1 ). The freshly prepared but not optimally oxidized K-MOF 2 and Rb-MOF 3 initially displayed intermediate band gaps and conductivity, however, upon prolonged aerobic oxidation, which raised the TTFTC˙ + population to saturation levels (∼25 and 10%, respectively), the resulting 2-ox and 3-ox displayed much narrower band gaps (∼1.35 eV) and higher electrical conductivity (6.6 × 10 −5 and 4.7 × 10 −5 S cm −1 , respectively). The computational studies indicated that charge movement in these MOFs occurred predominantly through the π-stacked ligands, while the experimental results displayed the combined effects of π–π-interactions, TTFTC˙ + population, and TTFTC/TTFTC˙ + IVCT interaction on their electronic and optical properties, demonstrating that IVCT interactions between the mixed-valent ligands could be exploited as an effective design strategy to develop electrically conducting MOFs. 

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4. Structure-Property Relationship Studies of Electrically Conductive Metal-Organic Framework Materials

   Zhang, Shiyu (May 2025, Clemson University, Tiger Prints https://open.clemson.edu/all_dissertations/3631)

   ABSTRACT Electricity is vital for modern life. With the rapid development of industries, society, and the ever-increasing population worldwide, the demand for electricity and advanced modern electronic devices with multifunctionality has increased tremendously. Therefore, advanced electronic materials that meet the requirements of the modern electronics and energy industry are needed. Electrically conductive metal-organic frameworks (EC-MOFs), composed of metal clusters acting as nodes and organic ligands as linkers connected by coordination bonds, are among the most promising materials due to their tunable structures, properties, and diverse functions. However, the lack of comprehensive understanding of their structure-property relationship hinders the development of EC-MOFs. My dissertation focuses on the design, construction, and structure-property relationship studies of EC-MOFs. Chapter 1 describes how MOFs' structural features and compositions affect the electronic properties and demonstrates conductive mechanisms and the corresponding design strategies to develop EC-MOFs. Chapter 2 describes the synthesis, characterization, electronic and optical properties, and structure-property relationships of four novel alkali metal (Na, K, Rb, and Cs) and an electron-rich tetrathiafulvalene tetracarboxylate (TTFTC) ligand-based 3D-MOFs where the ligands form continuous π-stacks and become partially oxidized by air forming TTFTC•+ radical cations. Depending on the π–π distance and TTFTC•+ population, the MOFs enjoyed different degrees of intervalence charge transfer (IVCT) interaction, which commensurately affected their band gaps and electrical conductivity. Chapter 3 depicts a novel design strategy to enhance the bulk electrical conductivity of 2D graphitic MOFs by promoting simultaneous in-plane and out-of-plane charge transport. To this end, we have synthesized the first π-intercalated two-dimensional graphitic MOF (iGMOF1) through an elegant bottom-up synthesis method. This novel structure featured hexagonal Cu-HATP (hexaaminotriphenylene, HATP) coordination network and built-in alternating π-donor/acceptor stacks of electron-rich HATP ligands and non-coordinatively intercalated π-acceptors hexacyano-triphenylene (HCTP) molecules, which simultaneously facilitated both in-plane and out-of-plane to endow iGMOF1 with higher bulk electrical conductivity compared to pristine Cu3(HATP)2. Chapter 4 describes design, synthesis, and structure-property relationship studies of a novel 2D Cu3(HOTP)(HHTQ) MOF based on a π-donor 2,3,6,7,10,11-hexahydrotriphenylene (HOTP) ligand and a π-acceptor 2,3,7,8,12,13-Hexahydroxytricycloquinazoline (HHTQ) ligand. The resulting framework featured continuous out-of-plane π-D/A stacks and in-plane hexagonal π-D-A sheets, promoting through-space and through-bond charge transport, respectively, which gave rise to a bulk electrical conductivity than pristine Cu3(HOTP)2 and Cu3(HHTQ)2. Finally, Chapter 5 describes the transformation of a collapse-prone, electrically insulating MOF-74 analog into structurally more stable, porous, and electrically conductive MOF/PEDOT composites. 

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5. Structure–property investigations in urea tethered iodinated triphenylamines

   https://doi.org/10.1039/D2CP01856J  

   Hossain, Muhammad Saddam; Ahmed, Fiaz; Karakalos, Stavros G.; Smith, Mark D.; Pant, Namrata; Garashchuk, Sophya; Greytak, Andrew B.; Docampo, Pablo; Shimizu, Linda S. (August 2022, Physical Chemistry Chemical Physics)

   Herein, we report structural, computational, and conductivity studies on urea-directed self-assembled iodinated triphenylamine (TPA) derivatives. Despite numerous reports of conductive TPAs, the challenges of correlating their solid-state assembly with charge transport properties hinder the efficient design of new materials. In this work, we compare the assembled structures of a methylene urea bridged dimer of di-iodo TPA (1) and the corresponding methylene urea di-iodo TPA monomer (2) with a di-iodo mono aldehyde (3) control. These modifications lead to needle shaped crystals for 1 and 2 that are organized by urea hydrogen bonding, π⋯π stacking, I⋯I, and I⋯π interactions as determined by SC-XRD, Hirshfeld surface analysis, and X-ray photoelectron spectroscopy (XPS). The long needle shaped crystals were robust enough to measure the conductivity by two contact probe methods with 2 exhibiting higher conductivity values (∼6 × 10 −7 S cm −1 ) compared to 1 (1.6 × 10 −8 S cm −1 ). Upon UV-irradiation, 1 formed low quantities of persistent radicals with the simple methylurea 2 displaying less radical formation. The electronic properties of 1 were further investigated using valence band XPS, which revealed a significant shift in the valence band upon UV irradiation (0.5–1.9 eV), indicating the potential of these materials as dopant free p-type hole transporters. The electronic structure calculations suggest that the close packing of TPA promotes their electronic coupling and allows effective charge carrier transport. Our results show that ionic additives significantly improve the conductivity up to ∼2.0 × 10 −6 S cm −1 in thin films, enabling their implementation in functional devices such as perovskite or solid-state dye sensitized solar cells. 

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