Mechanoluminescence from Amorphous Solids of Heteroleptic Copper Complexes and Common Luminophores Generated by Friction and Contact-Separation

A systematic study on mechanoluminescence in heteroleptic Cu(I) complexes revealed that in amorphous state, these complexes generate mechanoluminescence by friction and contact-separation through an inert layer even under ambient air. No polymer matrix is required to create amorphous mechanoluminescent films. We have unambiguously demonstrated that mechanoluminescent properties are observed in an amorphous state independently of whether mechanoluminescent properties are present or absent in the crystalline state: i.e. mechanoluminescence is observed in the amorphous state even for the Cu(I) complexes that are not mechanoluminescent in the crystalline state. Generation of mechanoluminescence by other types of mechanical stimuli through a double-film system is also demonstrated. These findings enabled a simple design to generate mechanoluminescence using a wide range of metal complexes and organic luminophores that overcomes the limitations of the crystalline state, offering a convenient approach for the development of flexible mechanoresponsive amorphous materials that respond to various types of mechanical actions, presumably via a mechanism involving triboelectrification and contact electrification.