Dual Free Radical Synergism for Enhancing Proton Conductivity in Photochromism iHOFs

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Stimuli-responsive smart materials offer reversible property changes under external triggers.
• Ionic hydrogen-bonded organic frameworks (iHOFs) are emerging materials with tunable structures and functions.
• Naphthalenediimide (NDI) incorporation enables photochromic properties in materials.

Purpose of the Study:

• To synthesize novel iHOFs with radical-driven photochromic behavior.
• To investigate the impact of UV irradiation on the proton conductivity of iHOFs and their composite membranes.
• To explore the synergistic effect of dual free radicals on material performance.

Main Methods:

• Synthesis of two iHOFs (36-37) via self-assembly of NDI derivatives and basic ligands.
• Characterization of iHOF proton conductivity under varying humidity and temperature.
• Incorporation of iHOF-37 into chitosan (CS) to form photochromic composite membranes.
• Evaluation of proton conductivity changes post-UV irradiation.

Main Results:

• iHOF-37 showed a baseline proton conductivity of 6.50 × 10⁻⁴ S·cm⁻¹ at 98% RH and 100 °C.
• UV irradiation significantly enhanced iHOF-37 proton conductivity by 14-fold to 9.10 × 10⁻³ S·cm⁻¹ due to dual radical synergism (NDI and viologen).
• The 5%-iHOF-37/CS composite membrane achieved proton conductivity up to 5.70 × 10⁻² S·cm⁻¹ (98% RH, 90 °C), increasing to 8.08 × 10⁻² S·cm⁻¹ after UV exposure.

Conclusions:

• Dual free radicals generated by NDI and viologen synergistically boost proton conductivity in iHOFs and composite membranes.
• The developed iHOFs exhibit promising photochromic properties and enhanced proton conductivity, suitable for stimuli-responsive applications.
• This research facilitates the rational design of advanced smart materials with tunable photoresponsive characteristics.