Ion Diffusion and (Photo)redox Conductivity in a Covalent Organic Framework.

Area of Science:

• Materials Science
• Electrochemistry
• Organic Chemistry

Background:

• Covalent Organic Frameworks (COFs) are advanced materials for energy applications, requiring controlled charge transport.
• Understanding charge transport mechanisms (band transport vs. electron hopping) in COFs is crucial but experimentally limited.
• Redox-active COFs offer potential for tunable electronic properties.

Purpose of the Study:

• To investigate redox hopping-mediated charge transport in a naphthalene diimide (NDI)-based COF.
• To examine the influence of ion and solvent environments on electron hopping.
• To explore the potential-dependent redox conductivity and switching behavior of COFs.

Main Methods:

• Synthesis of a TAPT-NDI COF.
• Potential step chronoamperometry to measure apparent electron diffusion coefficients.
• Modulation of NDI redox states using electrical potential and light.

Main Results:

• Electron hopping is significantly affected by ion size, ion pairing, and solvent polarity.
• First observation of a potential-dependent, bell-shaped redox conductivity profile in COFs.
• Conductivity enhancement by up to 4 orders of magnitude, enabling switching from insulating to semiconducting states.

Conclusions:

• Ion-coupled self-exchange is a key mechanism for redox hopping in COFs.
• COFs exhibit tunable conductivity, switching between insulating and semiconducting regimes.
• Findings pave the way for COFs in memristive devices, sensors, and (photo)electrocatalysis.