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Molecular Diode-Based Covalent Organic Frameworks: Imine Orientation-Driven Acid-Base Switching Photocatalytic H2
Tianyi Liu1, Yunjie Lang1, Ning Sun1
1Institute of Frontier Chemistry, School of Chemistry and Chemical Engineering, Shandong University, Qingdao, Shandong, China.
Researchers developed new donor-acceptor covalent organic frameworks (D-A COFs) that act like molecular diodes. These materials show switchable photocatalytic activity for hydrogen evolution, controlled by pH-responsive electron transfer.
Area of Science:
- Materials Science
- Photocatalysis
- Supramolecular Chemistry
Background:
- Donor-acceptor covalent organic frameworks (D-A COFs) show promise in photocatalysis due to porosity and charge separation.
- The influence of donor-acceptor linkage on charge transport and reaction selectivity in D-A COFs requires further investigation.
Purpose of the Study:
- To design and synthesize molecular diode-based COF isomers to investigate switchable electron transfer and photocatalytic hydrogen evolution.
- To elucidate the role of imine bond orientation and pH in regulating charge transport and reaction selectivity.
Main Methods:
- Synthesis of two molecular diode-based COF isomers (PyAm-PhAl-COF and PyAl-PhAm-COF).
- Systematic investigation of pH-responsive current rectification during photo-induced electron transfer.
- Measurement of photocatalytic hydrogen evolution rates under varying pH conditions.
Main Results:
- The synthesized COF isomers exhibited pronounced pH-responsive current rectification.
- PyAm-PhAl-COF showed a 172-fold higher hydrogen evolution rate under alkaline vs. acidic conditions.
- PyAl-PhAm-COF displayed a 25-fold higher activity under acidic vs. alkaline conditions, attributed to imine bond dipole reversal.
Conclusions:
- The study deepens the understanding of structure-performance relationships in D-A COFs.
- Imine bond orientation and its pH-responsive dipole change dynamically regulate electron transport and photocatalytic activity.
- A new design strategy for adaptive smart photocatalytic systems based on molecular diodes is proposed.
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