Mechanochromism of dinuclear aluminum-based triple-stranded helicates through crystalline-to-amorphous phase transition

Abstract

This study explores the mechanochromic behavior of dinuclear aluminum-based triple-stranded helicates with various halogenated substituents. Mechanical grinding induces distinct color changes, with powder X-ray diffraction confirming phase transitions between crystalline and amorphous states. In the crystalline phase, the helicates adopt a more twisted conformation that limits π-conjugation, producing monomeric yellow emission. In contrast, in the amorphous phase, this twist relaxes and the π-conjugated system is extended, yielding orange emission. The original emission properties can be restored through solvent treatment, demonstrating the reversible nature of this mechanochromic behavior. These results demonstrate a mechanochromic mechanism governed by reversible torsion-angle changes and highlight aluminum-based helicates as promising responsive luminescent materials.