Modeling of Different Ordering Schemes for Halogen-Functionalized Molecules with Triazine and Benzene Core

We propose a model based on pairwise intermolecular interactions explaining the occurrence of different structures in seemingly similar experiments of self-assembly of star-shaped 2,4,6-tris(4-halophenyl)-1,3,5-triazine (TXPT = TBPT, TIPT with X = Br and I) on solid surfaces. The model is universal and could be extended to analogous polyaromatic compounds with benzene core. Density functional calculations reveal that two main interactions of this system have different origins but very similar magnitudes (e(1) approximate to e(2)). This allows the formation of either e(1)-bonded or e(2)-bonded molecular ribbon-like structures. Along with the relation for the third main interaction, e(0) = 0.64e(1), we found two weaker complementary interactions and prepared the phase diagram of the TXPT system, which shows the domains of all four experimentally known structures in a tiny region of interaction parameters space. Using our model, we performed the ground-state analysis and extensive Monte Carlo simulations of the TXPT ensembles to substantiate our arguments. The results show that even a slight alteration in the balance of the main interactions leads to the self-assembly of different supramolecular networks. It is demonstrated that the row-like experimental phase may have several possible molecular arrangements with different bonding motifs and similar energies. The experimentally known coexistence of two phases is also reproduced in simulations.

Automated summary

Based on pairwise intermolecular interactions, a model is proposed to explain the occurrence of different structures in self-assembly experiments. It is found that even slight alterations in the balance of interactions can lead to the formation of different supramolecular networks.