Design and development of hydrogen bonded molecular assemblies based on pyromellitic diimide tethered carboxylic acids as optical materials†

Hydrogen bonded multi-component crystalline solids with desired physicochemical properties owing to their diverse potential applications have attracted great research attention. Minor differences in hydrogen bond interactions manipulate the molecular arrangements in the crystal lattice, leading to changes in physicochemical properties, such as solubility, stability, pharmaceutical, luminescence, etc. In this study, thorough understanding of the formation of different hydrogen bond patterns between the –COOH group and some specific but identical solvent molecules is presented. To this end, structural studies on six solvates of two isomeric pyromellitic diimide carboxylic acid host compounds (1 and 2) with dimethylformamide; DMF, (1a and 2a), dimethyl sulphoxide; DMSO, (1b and 2b) and 1,4-dioxane; Diox, (1c and 2c) guest solvent molecules were carried out. SCXRD structure analyses revealed that various types of donor–acceptor intermolecular interactions between the host–host, host–guest, and guest–guest molecules resulted in the formation of 3D supramolecular architectures of these solvates. Subtle differences in hydrogen bond patterns between the –COOH groups of isomeric host molecules and similar guest solvent molecules were observed in the structures of these solvates. DFT calculations on these different types of hydrogen bond motifs, either intermolecular rings (R) or non-cyclic intermolecular dyads (D), suggest that the same guest molecule can interact with the –COOH groups of isomeric host molecules in different ways. TGA for each solvate was consistent for the weight loss of solvent molecules according to the host–guest ratio which was further confirmed by the appearance of an endothermic peak in the same temperature region in each DSC diagram. The solid state fluorescence emission properties of both host compounds were found almost similar to their solvates, respectively, except for solvate 1c, which possesses two sets of symmetry non-equivalent guest Diox molecules in its crystal lattice, making a 3D channel architecture by the combination of hosts and one set of symmetry independent guest molecules. Overall, this study provides helpful insight into the formation of different hydrogen bond motifs between the two identical host–guest binding entities under the influence of steric orientations and other weak interactions.