Stability and formation process of hydrogen-bonded organic porous thin films: A molecular dynamics study

K Matsui and H Watanabe and TK Shimizu, AIP ADVANCES, 12, 105109 (2022).

DOI: 10.1063/5.0106036

Molecular dynamics simulation using the reactive force field was performed to investigate the stability and formation mechanisms of organic porous thin films made of 1,3,5-tris(4-carboxyphenyl) benzene (BTB) molecules fabricated at the air/water interface. A single-layer honeycomb structure is found to be unstable, whereas thicker films are stable, which is consistent with experimental findings. The slight corrugation of the existing film produces local charge variation that attracts isolated molecules via the Coulomb interaction. When the isolated molecule approaches the film, a hydrogen bond is formed, and then the molecule adjusts the adsorption configuration by itself to maximize both horizontal and vertical intermolecular interactions. The key to the initial hydrogen bond formation is suggested to be the density of the molecules provided in the system as well as the spontaneous alignment of the BTB molecules to the solution/water interface. Our study showed that the BTB film is stable, and the molecules are self-assembled without external forces in the quasi-two- dimensional system. These results suggest that the dominant factor for the film formation at the air/water interface is interactions among BTB molecules and confinement to the two-dimensional space. (c) 2022 Author(s).

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