Investigating the Mechanism of Triboluminescence: Insights from Structural and Electrostatic Characterization of Copper Thiocyanate Complexes

Triboluminescence is a phenomenon in which light is generated through mechanical stress; it has emerging applications in stress-sensing devices. Although the prevailing mechanistic model indicates that light emits from charge separation and recombination in fracture planes arising from polar structures, its application in designing triboluminescent materials remains limited owing to numerous exceptions. This study provides insights into the essential requirements for triboluminescence by investigating the structural and electrostatic properties of fractured crystals of copper thiocyanate complexes. The examined fracture plane indicated that charge pairs (which are essential for light emission) form when intermolecular interactions are disrupted during fracturing. On the basis of the nature of these charges, we successfully suppressed triboluminescence by inhibiting the formation of intermolecular interactions disrupted in the examined complexes. Furthermore, we induced its re-emergence by creating an alternative fracture plane through controlled manipulation of the molecular network. This demonstrative deactivation and reactivation of triboluminescence underscores the critical role of intermolecular disruption in generating charge pairs, a prerequisite for triboluminescence. The creation of oppositely charged pairs, followed by their recombination to exhibit triboluminescence upon disrupting intermolecular interactions during mechanical fracture of crystal, was characterized by X-ray analysis and theoretical calculations. This study elucidated the crucial role of charge separation in triboluminescence and enabled its activation and deactivation through molecular network design. image