A Computational Design of Covalently Bonded Mixed Stacking Cocrystals

In this study, a computational design of a new type of donor-acceptor mixed stacking cocrystals is introduced. Our approach involves functionalizing trisilasumanene frameworks with electron-donating groups (-CH₃, -OH, -NH₂) and electron-withdrawing groups (-F, -CN), and then stacking donors and acceptors alternatively while connecting them either by sp³- and sp-carbon chains. Using the B3LYP-D3/6-31+G(d) level of theory, we demonstrate that these covalently bonded cocrystals can overcome the issue of thermal and mechanical instabilities observed in the non-covalently mixed stacking. Furthermore, modifying donor and acceptor groups can vary the bandgaps, approximated by the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) gaps, from 1.50 to 3.50 eV. The results also predict the covalently bonded mixed stacking cocrystals having much larger conductance via Yoshizawa model. In addition, variations in bridge lengths were found to have a small effect on the HOMO-LUMO gaps but allow for a new control parameter regarding the porosity of the materials. These results encourage experimental explorations.