Mechanofluorochromic or piezochromic fluorescence chemistry involves the switching and tuning of the luminescent properties of solid-state materials induced by exogenous forces, such as grinding, shearing, compression, tension, and so forth. Up until now, most reported mechanochromic systems, including liquid crystals, organic molecules, organometallic compounds, polymers, and dye-doped polymers, have displayed reversible two-color changes, which arise from either supramolecular or chemical structure transformations. However, fluorescent materials that undergo mechanically induced multicolor changes remain rare; this Minireview is focused on such materials. Topics are categorized according to the different applied forces that are required to induce the multicolor change, including mechanical control of either the supramolecular structures or the chemical structures, and mechanical control of both the supramolecular structures and chemical structures.

Asserting its independence: A single organic molecule containing pyrene and rhodamine B chromophores separated by a peptide spacer formed a mechanochromic material whose fluorescence could be switched from blue to bluish-green and reddish by grinding. Modulation of the overlapped packing pattern of the pyrene excimer for blue emission was crucial for the reversible tricolored switching observed.

A smart luminescent material whose emission color and emission intensity can be separately modulated by external force is demonstrated. The rational manipulation of rich noncovalent interactions and fluorophore packing style promotes an in-depth understanding between supramolecular structure and photophysical property and offers an effective strategy to modulate the light-emitting property in a predicative way.