Self-assembled supramolecular frameworks via intermolecular interactions in acridine and dihydroxybenzene cocrystals: a study of structure‒property relationship

Cocrystals of acridine with 1,2-dihydroxybenzene (I), 1,3-dihydroxybenzene (II), 1,4-dihydroxybenzene (III), and 2,2′-dihydroxybiphenyl (IV) have been synthesized and characterized via single-crystal X-ray diffraction. The supramolecular self-assembly of molecules results in one-dimensional tape, two-dimensional square grids, two-dimensional sheets, and three-dimensional architectures in the crystal structures via O‒H···N, O‒H···O hydrogen bonds and C‒H···O, C‒H···N, π···π, C‒H···π interactions. In three-dimensional molecular packing, the acridine molecules form one-dimensional continuous π…π stacking chains in parallel and off-set manners. The charge distribution and molecular reaction mechanism of cocrystals have been studied via molecular electrostatic potential (MEP) and frontier molecular orbital (FMO) calculations. The photophysical properties of the cocrystals and pure acridine were studied via solid-state photoluminescence characterization. The photoluminescence emission maximum (λ_max) of pure acridine was at 420 nm, and for the cocrystals, it was at 446 (I), 481(II), 485(III), and 467(IV) nm, respectively. The results revealed that the acridine emission was most strongly blue-shifted, whereas the fluorescence emission maxima of the cocrystals were redshifted up to 65 nm compared with those of single-molecule acridine crystals. This discussion revealed that the photophysical properties of acridine and dihydroxybenzene cocrystals can be tuned by the position of the hydroxyl substituent and the nature of the intermolecular interactions between the molecules.