The discovery of ballistic charge transport in graphene ignited the quest for two-dimensional (2D) materials and they are now used in various applications, such as electronics and materials science. In particular, 2D π-conjugated covalent organic frameworks (COFs) received much attention due to their wide structural tunability, large surface area, and numerous associated properties.
The Perepichka group at McGill University designed a new π-conjugated COF based on trioxaazatriangulene (TANG) – a highly electron-rich and rigid building block of triangular symmetry. The COF was synthesized as a black crystalline powder via dynamic polycondensation reaction of in-situ prepared triaminated TANG with dihydroxyterephthalic aldehyde. The optical and electrochemical measurements of the COF reveal a bandgap of ~1.2 eV. The COF can be readily doped with iodine resulting in a dramatic reduction of the band-gap (<0.2 eV), intrinsic conductivity (0.01 S/cm), and paramagnetic behavior down to 20K.
DFT calculations using AMS-BAND module have helped develop a symmetry constraint and determine the layering structure of TANG. Additional DFT calculations predicts an anisotropic charge transport brought about by π-stacking of 2D covalent TANG networks. Indeed, while individual 2D polymer layers feature a large bandgap (1.81 eV) and a little dispersion in HOCO (0.28 eV) and LUCO (~0 eV), their stacking results in a much narrower bandgap (0.80 eV) and significant band dispersion along the π-stacking direction (0.95 eV for HOCO). The experimental measurements in anisotropically compressed COF pellets confirmed these DFT predictions.
Do you want try for yourself? Request a free 30-day evaluation for the whole Amsterdam Modeling Suite.
Newsletter: tips & tricks, highlights, events
Would you like to keep up to date with the latest developments in the Amsterdam Modeling Suite and the SCM team, learn more about new applications and functionality?
Subscribe to our newsletter!
You have already subscribed. Thank you! If you don't receive our newsletters, send us an email.
Lakshmi, V.; Liu, C. H.; Rajeswara Rao, M.; Chen, Y.; Fang, Y.; Dadvand, A.; Hamzehpoor, E.; Sakai-Otsuka, Y.; Stein, R. S.; Perepichka, D. F. A Two-Dimensional Poly(azatriangulene) Covalent Organic Framework with Semiconducting and Paramagnetic States. J. Am. Chem. Soc. 2020, 142, 2155–2160.
Key conceptsADF BAND materials science organic electronics semiconductors