Despite recent extensive studies on mechanochromic luminescence (MCL), rational control over the magnitude of the emission-wavelength shift in response to mechanical stimuli remains challenging. In the present study, a twocomponent donor-acceptor approach has been applied to create a variety of organic MCL composites that exhibit remarkable emission-wavelength switching. Dibenzofuranbased bis(1-pyrenylmethyl)diamine and typical organic fluorophores have been employed as donor and acceptor dyes, respectively. Outstanding wide-range MCL with an emission-wavelength shift of over 300 nm has been achieved by mixing the diamine with 3,4,9,10-perylenetetracarboxylic diimide. Unprecedented two-step MCL in response to mechanical stimuli of different intensity has also been realized for a twocomponent mixture with 9,10-anthraquinone. Fluorescence microscopy observations at the single-particle level revealed that the segregation and mixing of the two-component dyes contribute to the stimuli-responsive emission-color switching of the MCL composites.

Despite the recent increased interest in organic small molecule luminophores that exhibit circularly polarized luminescence (CPL) or mechanochromic luminescence (MCL), MCL behavior in chiral luminophores that display solid‐state CPL still remains elusive. Herein, it is reported that a chiral diamine‐linked bispyrene derivative exhibits a rare MCL behavior in response to two different types of mechanical stimuli, namely utrasonication and grinding. Moreover, an unprecedented switching of solid‐state CPL has been achieved for the chiral bispyrene between two states that can respond to the different mechanical stimuli. These findings should help to advance the development of practical CPL materials.

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The creation of two‐component dyes has proven to be an effective strategy to achieve remarkable mechanochromic luminescence (MCL) properties. The shift of the maximum emission wavelength (Δλem) range of a bis(1‐pyrenylmethyl)diamine derivative has been significantly improved by mixing it with typical organic dyes that do not exhibit MCL behavior. Most notably, a wide‐range MCL (Δλem=340 nm) has been achieved for a mixture with 3,4,9,10‐perylenetetracarboxylic diimide. Furthermore, a two‐step MCL has been realized by mixing with 9,10‐anthraquinone. More information can be found in the Full Paper by S. Ito, T. Tachikawa, et al. (DOI: 10.1002/chem.202102700).

The front cover artwork is provided by Suguru Ito, Yoshitane Imai, and co‐workers at Yokohama National University, Kobe University, and Kindai University (Japan). The image shows circularly polarized luminescence of monomer and excimer emission in response to two mechanical stimuli. Read the full text of the Article at 10.1002/cptc.202100087.