Interdigitation and Hydrogen Bonding in Benzotriazole-Based 2D Layered Perovskites: a Study of Organic Non-Covalent Interactions

Extensive research in the past decade has shown that hybrid perovskites might become a cornerstone in the future global energy economy. Although three-dimensional 3D perovskites have been receiving a lot of research attention, their 2D layered counterparts have also been proven valuable to the field. In state-of-the-art 2D layered perovskites, alkylammonium and phenethylammonium cations are still mostly employed. Although these organic cations succeed in stabilizing the perovskite, they don’t offer valuable properties of their own to complement the attractive optoelectronic properties of the perovskite layers. Synergy could be achieved by choosing larger organic cations with more suitable optoelectronic properties, [1,2] or by inserting organic charge-transfer complexes [3] or dipole stacks in the organic layers. However, the non-covalent interactions acting within these more advanced organic layers need to be fully understood in order to formulate design rules and structure-property relationships for this novel class of materials.<br/><br/>In this work, [4,5] benzotriazole-based organic cations are synthesized and subsequently successfully applied to 2D layered hybrid perovskites. The structural and thermal properties of thin films and single crystals of these perovskites are investigated. Single-crystal analysis reveals that benzotriazole-based organic layers in lead(II) iodide lattices show interdigitation, reducing the organic layer thickness and leading to an unusually dense aromatic stacking. Moreover, 2D layered benzotriazole perovskites contain hydrogen bridges – both inter- and intramolecular – within the organic layers. Through theoretical modelling using density-functional theory (DFT), we elucidate this interdigitation and hydrogen bonding and quantify the lattice stabilization. We relate the phenomenon of interdigitation to the available lattice space and to stabilizing non-covalent interactions. Finally, we show that these structural properties lead to enhanced thermal stability with respect to the state of the art.<br/><br/><b>References</b><br/>[1] R. Herckens, W. T. M. Van Gompel et al., <i>J. Mater. Chem. A</i> (2018), 6, 22899.<br/>[2] P.-H. Denis, M. Mertens et al., <i>Adv. Opt. Mater.</i> (2022), 10, 2200788.<br/>[3] W. T. M. Van Gompel, R. Herckens et al., <i>Chem. </i><i>Commun.</i> (2019), 55, 2481.<br/>[4] A. Caiazzo, <u>A. Maufort</u> et al., <i>ACS Appl. Energy Mater.</i> (2023), 6, 3933.<br/>[5] A manuscript by the authors on organic non-covalent interactions in 2D layered perovskites is being prepared.