Charge-Transfer Assembly of Electrically Conductive Metal-Organic Cages

We report a strategy for utilizing metal-organic cages (MOCs) as building blocks for assembling porous materials with high electrical conductivity. Realizing conductivity in porous materials would unlock their potential in electrocatalytic and energy storage applications, but current materials with these properties are stymied by poor control over their physical form factors. The molecular nature of MOCs enables solution processability while also preserving permanent porosity, but the lack of formal bonds between discrete units has prevented the formation of conductive pathways. We show that by appending electron-donating tetrathiafulvalene (TTF) groups to the surface of the MOC, and then reacting these cages with the molecular electron-acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄TCNQ), electrically conductive character can be introduced to reach conductivities on the order of 10^-6 S/cm. This conductivity is achieved without sacrificing the intrinsic porosity of the cage, as confirmed by gas and guest uptake experiments. Clear evidence of electron transfer between the appended donors and molecular acceptors creates a highly tunable charge-transfer assembly motif and establishes MOCs as building blocks for targeting electrically conductive, porous materials.