Structural Control of Band Gap and Polaron Delocalization in 2D Azatriangulene Covalent Organic Frameworks

New two-dimensional (2D) covalent organic frameworks (COFs) with a tri(oxa)azatriangulene (TANG) node and different polarity of the imine linkers (C=N vs N=C) and internode distance have been synthesized using a trans-imination polymerization. The orientation of the imine linker controls the donor-acceptor interactions in these π-conjugated COFs, resulting in a large modulation of the valence band maximum (–4.2 to –5.4 eV) and the band gap (Eg ≈ 1.2-1.6 eV). p-Doping of COFs in iodine vapor improves the -conjugation and results in the formation of highly delocalized polarons with an absorption band extending into the far-infrared (THz band) region. Reducing the TANG-TANG internodal distance increases the 2D band-width dispersion; upon doping, the corresponding COF shows the highest (in the series) electrical conductivity (10⁻¹ S/cm), lowest conductance activation energy (50 meV near room temperature), and the most red-shifted polaron absorption (edge ~160 m, 8 meV).