Mechanofluorochromism (MFC) of Donor <i>–π</i> –Acceptor (D <i>–π</i> –A)‐Type Fluorescent Dyes

Mechanofluorochromism (MFC) is a photophysical phenomenon in which the color and fluorescent color of solid-state organic or metal complex fluorescent dyes change upon external mechanical stimulation (grinding) and recover to their original ones upon heating or exposure to solvent vapor. We discovered that newly developed donor-π-acceptor (D-π-A) fluorescent dyes exhibit bathochromic or hypsochromic-shifted MFC (b-MFC or h-MFC). This MFC arises from reversible switching between the crystalline and amorphous states, accompanied by changes in dipole-dipole and intermolecular π-π interactions upon grinding and heating. Indeed, such MFC not only is of a great scientific interest in photochemistry and photophysics but also has great potential for development of smart materials for next-generation optoelectronic devices, including rewritable photoimaging and electroluminescence devices. In this Personal Account, we offer an insight into the mechanism for the expression of MFC and present molecular design directions for creating D-π-A-type mechanofluorochromic dyes which can exhibit b-MFC or h-MFC.