Supramolecular Organic Frameworks Based on Cyclic Aromatic Imides Tethered to Carboxylic Acid Hosts and Aromatic N-Heterocyclic Solvent Guests

Abstract

Structural aspects of eight solvates comprising two pyromellitic diimides (PMDIa and PMDIb) and two naphthalene diimides (NDIa and NDIb) tethered to isomeric carboxylic acid hosts with pyridine (py) and quinoline (qn) guests are studied. The roles of different types of noncovalent interactions such as hydrogen bonding and π-stacking in the formation of diverse supramolecular host–guest networks are described. Minor differences in the host–host and host–guest weak interactions led to the formation of both the supramolecular tight-packed networks for solvates PMDIapy, PMDIbpy, and NDIbpy and the supramolecular channeled architectures for solvates PMDIaqn, PMDIbqn, NDIapy, NDIaqn, and NDIbqn, respectively. The guest solvent molecules reside inside the channels/cavities of different dimensions in such 3D assemblies, weakly interacting with the host molecules. Remarkably, three different hydrogen bond motifs including three qn guests and a −COOH group with cyclic and discrete patterns are also identified in the quinoline solvates. DFT calculations on these unprecedented motifs authenticated the possibility of the formation of either motif in the solid state. The photoluminescence properties of the solvates revealed almost similar emissions for the solvates of PMDI hosts at 455 nm but different emissions for the solvates of NDI hosts in the range of 448–485 nm. Thermal analyses (TGA and DSC) validated the host–guest stoichiometries and decomposition temperature regions of the solvates. In general, this study looks at how weak interactions between π-electron-deficient aromatic imides and π-electron-rich aromatic guests affect the formation of supramolecular assemblies of solvates and their optical properties.