Computational Modeling and Self-Assembly Synthesis of Borazine-Based Free-Standing Molecular-Thin Films.

Boron-nitride-rich organic thin materials based on borazines have gained significant attention for their potential in nano(opto)electronic and energy storage devices. We address synthetic challenges in producing effective borazine-based thin films by proposing a dual theoretical and experimental protocol. This combines a multiscale computational approach, using density functional theory and classical molecular dynamics, with synthesis and thin-film formation via the Langmuir-Blodgett technique. The computational modeling focuses on three key properties: π-π stacking interactions, molecular steric hindrance, and dynamic self-assembly orientation. This modeling guided the selection of a borazine molecular building block and enabled the successful experimental formation of a free-standing molecular-thin borazine-based film. Solely π-π stacking interactions were found to drive the formation of a bilayer film with a molecular thickness of 2.1 nm, capable of spanning 0.6 μm diameter holes as a free-standing film. The agreement between theory and experiment confirms that the film retains essential features of the borazine molecular crystal, particularly intermolecular offset face-to-face π-π stacking and hexagonal-based pattern orientations. We thus establish a robust and transferable approach for modeling and synthesizing borazine-based thin materials, deepen the understanding of molecular interactions in borazine self-assembly, and demonstrate the suitability of the Langmuir-Blodgett technique for fabricating borazine-based 2D materials.