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 to exploring the 3D topology of 2D tessellations of a naphthalene diimide-based molecular triangle (<b>NDI-Δ</b>) reveals that the 2D molecular arrangement is sensitive to the identity of the solvent and solute concentrations. Utilization of nonhalogenated solvents, combined with careful tailoring of the concentrations, results in <b>NDI-Δ</b> self-assembling though [π···π] interactions into 2D honeycomb triangular and hexagonal tiling patterns. Cocrystallization of <b>NDI-Δ</b> with tetrathiafulvalene (<b>TTF</b>) leads systematically to the formation of 2D tessellations as a result of superstructure-directing CT interactions. Different solvents lead to different packing arrangements. Using MeCN, CHCl₃, and CH₂Cl₂, we identified three sets of cocrystals, namely <b>CT-A</b>, <b>CT-B</b>, and <b>CT-C</b>, respectively. Solvent modulation plays a critical role in controlling not only the <b>NDI-Δ</b>:<b>TTF</b> stoichiometric ratios and the molecular arrangements in the crystal superstructures, but also prevents the inclusion of <b>TTF</b> guests inside the cavities of <b>NDI-Δ</b>. Confinement of <b>TTF</b> inside the <b>NDI-Δ</b> cavities in the <b>CT-A</b> superstructure enhances the CT character with the observation of a broad absorption band in the NIR region. In the <b>CT-B</b> superstructure, the CHCl₃ lattice molecules establish a set of [Cl···Cl] and [Cl···S] intermolecular interactions, leading to the formation of a hexagonal grid of solvent in which <b>NDI-Δ</b> forms a triangular grid. In the <b>CT-C</b> superstructure, three <b>TTF</b> molecules self-assemble, forming a supramolecular isosceles triangle <b>TTF-Δ</b>, which tiles in a plane alongside the <b>NDI-Δ</b>, producing a 3 + 3 honeycomb tiling pattern of the two different polygons. Solid-state spectroscopic investigations on <b>CT-C</b> 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 <b>TTF</b>^<b>•+</b> radical cations and one neutral <b>TTF</b> molecule.