Solvent-assisted planar structure of a stilbene-based salicylhydrazone compound: crystal structure, solvent- and aggregation-induced emission, and switchable luminescence colouration.

A novel stilbene-based salicylhydrazone compound {systematic name: (E)-4,4'-(ethene-1,2-diyl)bis[(N'E)-N'-(2-hydroxybenzylidene)benzohydrazide] dimethyl sulfoxide disolvate, CHNO·2CHOS or L·2DMSO} was synthesized and characterized by single-crystal X-ray diffraction, powder X-ray diffraction and luminescence spectroscopy. The title compound crystallizes in the monoclinic space group P2/c, with half a symmetry-independent L molecule and one dimethyl sulfoxide (DMSO) solvent molecule in the asymmetric unit. The L molecule adopts an almost planar structure, with a small dihedral angle between the planes of the stilbene and salicylhydrazone groups. There are multiple π-π stacking interactions between adjacent L molecules. The DMSO solvent molecules act as proton donors and acceptors, forming hydrogen bonds of various strengths with the L molecules. In addition, the geometry optimization of a single molecule of L and its luminescence properties either in solution, as a solvated solid or as a desolvated solid were studied. The compound shows an aggregation-induced emission (AIE) effect and exhibits switchable luminescence colouration in the solid state by the simple removal or re-addition of the DMSO solvent.