Metal-organic frameworks (MOF), as the name suggests, are self-assembled from metal ions or clusters as nodes and organic ligands as linkages through coordination bonds. Electrically conducting MOFs have become one of the most promising electronic materials due to their diverse potential applications in charge and energy storage, chemiresistive sensing, electrocatalysis, light-harvesting systems, etc. However, compared to conductive 2D-MOFs, which usually contain highly effective through-bond charge movement pathways and display high intrinsic electrical conductivity, it is much more challenging to develop electrically conducting 3D-MOFs and requires a deep understanding of their structure-property relationships.<br/>Herein, four novel alkali-metal-based (Na, K, Rb, and Cs) 3D-MOFs with continuous π-stacks using an electron-rich tetrathiafulvalene tetracarboxylate (TTFTC) ligand were constructed to demonstrate how the structures and components of MOFs affect their electrical properties, including electrical conductivity, electronic and optical band-gaps. Because of the π–π interaction and population of aerobically generated TTFTC radical cations, these MOFs underwent different extent of TTFTC/TTFTC radical cations intervalence charge transfer (IVCT) interactions, which facilitated the charge delocalization and, in turn, promoted the π–π interaction. Finally, the effects of TTFTC/TTFTC radical cations IVCT interaction, TTFTC radical cations population, and π–π interaction, determined by π–π distances and π–π overlaps, influenced the electrical conductivity and band-gaps. This study demonstrated that electrical conductive MOFs could be developed via IVCT interactions between the π-stacked mixed-valent ligands, providing a promising design strategy.

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

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