Tricolor mechanochromic luminescence of an organic two-component dye: visualization of a crystalline state and two amorphous states†
Solid-state emissive dyes with mechanochromic luminescence (MCL) properties change their emission colors upon exposure to mechanical stimuli. During the recent rapid advances in the area of MCL, considerable efforts have been focused on elucidating the MCL behavior of single-component dyes that can switch their solid-state emission between two colors. Herein, a novel strategy to achieve tricolor MCL is presented, which is based on mixing two organic dyes that exhibit poor MCL or no MCL properties, respectively. We propose that the tricolor MCL of the two-component dye should be attributed to the transition of the fraction with poor MCL properties from a crystalline to two amorphous states, specifically a perfectly amorphous and a proto-crystalline amorphous state. The present system should have advantages in terms of the availability of MCL dyes and the variety of potential combinations of two-component dyes. By making a use of the underlying design principle developed in this study, a wide variety of new MCL systems should be accessible, which should also accelerate the investigation of practical applications of MCL dyes.