Luminescence Mechanochromism of an Anionic Dinuclear Copper Iodide Complex

This article reports the mechanochromic luminescence properties of a copper iodide complex formulated (PrPh₃P)₂[Cu₂I₄] (<b>1</b>), which displays a contrasted reversible emission color switch from green (λ_max = 535 nm) to yellow (λ_max = 565 nm), upon mechanical solicitations. In addition to being a rare example of an ionic dinuclear copper-based mechanochromic compound, this complex is capable of congruently melting at a relatively low temperature (159 °C) to form a yellow emissive glassy phase (λ_max = 590 nm).

This amorphous state is considered as the reference state of the partial crystalline-to-amorphous transformation that occurs upon grinding. Comparison of these two amorphous phases helps mechanism investigations. In particular, solid-state NMR (nuclear magnetic resonance) analysis allowed quantification of the amorphous fraction, constituting 23% of the mechanically altered phase.