Coordination driven self-assembly of donor-acceptor linkers in 3D supramolecular frameworks: Ground state charge transfer and tunable porosity

We report the synthesis, structural characterization and photophysical properties of two 3D supramolecular architectures formed by the coordination driven self-assembly of pyrene and Schiff base linkers, as a donor-acceptor (D-A) pair. The monotopic functionality of the pyrene (as pyrenemonocarboxylic acid and pyrenebutyric acid) and ditopic Schiff base with Cd2+ render 1D coordination polymers (CPs), which are interdigitated via non-covalent interactions to form 3D supramolecular frameworks. The pyrenemonocarboxylic acid containing CP forms a dense structure, while the pyrenebutyric acid containing CP is porous and dynamic, as confirmed by the gas and solvent vapour adsorption experiments. Structural insight from the X-ray crystal structures and photophysical characterizations of the CPs reveal that pyrene and Schiff base form a stable charge transfer (CT) state. The variable alkyl chain lengths of the pyrene linkers tune the porosity, however, allow strong π-π and C–H-π interactions among the D-A units rendering facile CT, as confirmed by EPR and DFT calculations.