Hydrogen Bond‐Directed Molecular Packing and Dual Mechano chromic Luminescence of an Acylhydrazone‐Based Derivative in the Solid State and Its Application in Detection of Al 3+ Ion

N‐(4‐Diethylamino‐2‐hydroxylbenzylidene)‐3‐hydroxy‐2‐naphthohyd‐ razide (H 3 L) was synthesized at 80 °C and 110 °C, and H 3 L 80 and H 3 L 110 crystals were obtained. They have the same composition. The structural analysis showed that H 3 L 80 and H 3 L 110 are composed of one dimensional supramolecular chains via intermolecular O‐H … O and C‐H … O hydrogen bonds, which are further assembled to supra‐molecular networks through intermolecular C‐H … O bonds between 1D chains, resulting in their unique molecular packing modes. H 3 L 80 crystals emitted at 530 nm and H 3 L 110 crystals emitted at 610 nm under 465 nm light. The largely red‐shifted emission for H 3 L 110 is attributed to the enhancement of molecular planarization and π‐conjugation of H 3 L 110 compared to H 3 L 80 . The dual mechanochromic luminescence of H 3 L 80 and H 3 L 110 fluorophor could be reversibly carried out by grinding of H 3 L 80 and H 3 L 110 crystals and subsequent recrystallization of H 3 L 80 and H 3 L 110 samples. The microstructural stability of H 3 L 110 was concentration‐dependent in solutions, such as DMSO, DMF and THF, resulting in change of fluorescence property. But, H 3 L 80 microstructure was stable in solutions. H 3 L 80 could be used to detect Al (III) ion with high selectivity and sensitivity in aqueous medium. Also, H 3 L 80 could detect intracellular Al 3+ ions.