Versatile Mechanochromic Luminescence by Organic Crystals

Abstract

Great studies have been made in the past decade toward the development of solid-state emissive materials that exhibit mechanochromic luminescence (MCL), i.e., mechanical-stimuli-induced reversible color change of the solid-state emission. However, the generation of organic crystals with specific MCL behavior remains a challenging task due to the lack of the design principle of MCL-active crystals. Herein, a systematic study of indolylbenzothiadiazoles as self-recovering MCL-active organic crystals with different emission colors and recovery times is described. In addition, a series of phenanthroimidazolylbenzothiadiazoles exhibit more versatile MCL properties. Bathochromically or hypsochromically shifted bicolor MCL as well as tricolor MCL are observed due to the formation of different crystal structures. We also propose a novel strategy to achieve tricolor MCL, which is based on crystals of mixed two organic dyes. The underlying design principle obtained in these studies should accelerate the development of a wide variety of new MCL materials.