Mechano-Luminescent Behavior of a Pyridine-Containing Anthracene Derivative: Role of Aromatic Stacking Interactions

Isonicotinic acid anthracen-9-ylmethylene-hydrazide (AI), prepared from anthracene-9-carboxaldehyde and isoniazid, exhibited mechano-responsive luminescent emissions; for instance, gentle pressing of the weakly emissive crystals of AI (λem 527 nm) produced a yellow-green emissive material (λem 540 nm). Also, the mechano-luminescent emissions of AI could be easily switched “off” upon exposure to N,N-dimethylformamide. Contrastingly, under the same conditions, benzoic acid anthracen-9-ylmethylene-hydrazide (AB) did not exhibit mechano-responsive luminescent emissions. On the basis of UV–vis, fluorescence, Fourier transform infrared spectroscopy, and powder X-ray diffraction (XRD) studies, we suggest that mechano-luminescent emissions of AI were triggered by mechanically induced deformations in the lattice, which affected the intermolecular interactions and aromatic stacking behavior. Again, the mechano-luminescent emissions of AI were switched off when mixed with oxalic acid, although accompanied by a concomitant change in color, from yellow-green to red. Single crystal XRD studies provided vital insights into the interactions of AI with oxalic acid, highlighting the role of hydrogen bonding and anion-mediated aromatic-π interactions.