Mechanoluminescence from amorphous solids of heteroleptic copper complexes and common luminophores induced by non-destructive mechanical stimuli and fabrication of flexible mechanoluminescent films

A systematic study on mechanoluminescence in heteroleptic Cu^I complexes revealed that in the amorphous state, these complexes generate mechanoluminescence by friction as well as non-destructive stimuli such as contact-separation through an inert layer without direct physical damage to them, even under ambient air. No fracturing of the crystalline solids and no polymer matrix are required. Our findings overcome the limitations of the reported molecular crystalline mechanoluminescent materials generating luminescence by fracturing the crystalline solids, and enable a simple material design to develop non-crystalline flexible mechanoluminescent materials using photoluminescent molecules, which emit light under various non-destructive mechanical stimuli, including bending and twisting. The detailed study shows that the mechanism involves the generation of a strong electric field on the contact surface between two materials, caused by triboelectrification and contact electrification, which leads to the excitation of molecules.