Greatly Enhanced the Electrical Conductivity of Flexible Cu-MOF Thin Film via the Interaction with Redox-Active Guest Molecules

Conductive metal-organic frameworks (MOFs) are of considerable importance because of their potential applications in various electronics. And integrating conductive MOFs with flexible substrates represents a promising strategy for preparing different flexible electronic devices. This study first developed a flexible and highly conductive TCNQ@Cu-BDC film on a polyester fabric substrate. Here, a copper layer was first deposited on the substrate via magnetron sputtering, converted into Cu(OH)₂ nanowire templates through alkaline solution treatment, and subsequently transformed into a Cu-BDC MOF film via hydrothermal synthesis. Then the redox-active, conjugated 7,7,8,8-tetracyanoquinodimethane (TCNQ) guest molecules were introduced into the pores of activated Cu-BDC MOF through liquid-phase doping, and the electrical conductivity of TCNQ@Cu-BDC film is remarkably enhanced by ∼2 orders of magnitude (approximately 180-fold increase) compared with the pristine MOF. Characterization demonstrates that when the TCNQ molecules are incorporated into the pores of Cu-BDC, they can occupy the open copper sites and can simultaneously undergo redox reactions with the organic ligands. During this process, the organic ligands are oxidized, and some Cu²⁺ ions are reduced as TCNQ²⁻ ions are generated, which promotes the transfer of electric charges among the MOF framework and significantly improves the electric conductivity of the host-guest system.