Azatriangulene-Based Conductive C═C Linked Covalent Organic Frameworks with Near-Infrared Emission
Ehsan Hamzehpoor1, Pegah Ghamari1, Yuze Tao1
1Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec, H3A 09B, Canada.
Abstract:
Two near-infrared (NIR) emissive π-conjugated covalent organic frameworks (COFs) pTANG1 and pTANG2 are synthesized using Knoevenagel condensation of trioxaazatriangulenetricarbaldehyde (TATANG) with benzene- and biphenyldiacetonitriles, respectively. The morphology of the COFs is affected by the size of TATANG precursor crystals. Donor-acceptor interactions in these COFs result in small bandgaps (≈1.6 eV) and NIR emission (λmax = 789 nm for pTANG1). pTANG1 can absorb up to 9 molecules of water per unit cell, which is accompanied by a marked quenching of the NIR emission, suggesting applications as humidity sensors. p-Doping with magic blue significantly increases the electrical conductivities of the COFs by up to 8 orders of magnitude, with the room temperature conductivity of pTANG1 reaching 0.65 S cm-1, the highest among reported C═C linked COFs. 1H NMR relaxometry, temperature-dependent fluorescence spectroscopy, and DFT calculations reveal that the higher rigidity of the shorter phenylene linker is responsible for the more extended conjugation (red-shifted emission, higher electrical conductivity) of pTANG1 compared to pTANG2.
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