Supramolecular tessellations by a rigid naphthalene diimide triangle

Tessellation of organic polygons though [π⋯π] and charge-transfer (CT) interactions offers a unique opportunity to construct supramolecular organic electronic materials with 2D topologies. Our approach of exploring the 3D topology of 2D tessellations of a naphthalene diimide-based molecular triangle (NDI-δ) reveals that the 2D molecular arrangement is sensitive to the identity of the solvent and solute concentrations. Utilization of non-halogenated solvents, combined with careful tailoring of the concentrations, results in NDI-δ self-assembling though [π⋯π] interactions into 2D honeycomb triangular and hexagonal tiling patterns. Co-crystallization of NDI-δ with tetrathiafulvalene (TTF) leads systematically to the formation of 2D tessellations as a result of superstructure directing of CT interactions. Different solvents lead to different packing arrangements. Using MeCN, CHCl₃ and CH₂Cl₂, we identified three sets of co-crystals, namely CT-A, CT-B, and CT-C respectively. Solvent modulation plays a critical role in controlling, not only the NDI-δ:TTF stoichiometric ratios and the molecular arrangements in the crystal superstructures, but also prevents the inclusion of TTF guests inside the cavities of NDI-δ. Confinement of TTF inside the NDI-δ cavities in the CT-A superstructure enhances the CT character with the observation of a broad absorption band in the NIR region. In the CT-B superstructure, the CHCl₃ lattice molecules establish a set of [ClCl] and [ClS] intermolecular interactions, leading to the formation of a hexagonal grid of solvent in which NDI-Δforms a triangular grid. In the CT-C superstructure, three TTF molecules self-assemble, forming a supramolecular isosceles, triangle TTF-δ, which tiles in a plane alongside the NDI-δ producing a 3+3 honeycomb tiling pattern of the two different polygons. Solid-state spectroscopic investigations on CT-C, revealed the existence of an absorption band at 2500 nm which, on the basis of TDDFT calculations was attributed to the mixed-valence character between two TTF•+ and one neutral TTF molecule.