N-Boc-Indolylbenzothiadiazole Derivatives: Efficient Full-Color Solid-State Fluorescence and Self-Recovering Mechanochromic Luminescence.

Herein, the solid-state emission with good fluorescence quantum yields of N-Boc-indolylbenzothiadiazoles as a new class of fluorophores is described. Their solid-state emission covers the wide range of the visible spectrum and the emission color can be tuned easily by changing the substituents on the two heteroaromatic rings. Among these, 3-methylindolyl derivatives exhibit moreover autonomously self-recovering mechanochromic luminescence, whereby the original solid-state emission could be recovered spontaneously at room temperature after exposure to a mechanical stimulus. The emission color, as well as the recovery time for the color change could be tuned via the introduction of different substituents on the benzothiadiazole ring. We propose that the mechanism of the autonomously self-recovering mechanochromic luminescence of 3-methylindolylbenzothiadiazoles is based on a partial amorphization of the crystals upon exposure to the mechanical stimulus, followed by autonomous recovering in the form of recrystallization.