Mechanochromism of Dinuclear Aluminum-based Triple-stranded Helicates through Crystalline-to-Amorphous Phase Transition

Abstract

This study explores the mechanochromic behavior of dinuclear aluminum 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 relaxes 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 findings demonstrate the potential of aluminum-based helicates as unique responsive luminescent materials.