Mechanically Induced Multicolor Change of Luminescent Materials

Abstract

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.

A Thermo‐ and Mechanoresponsive Cyano‐Substituted Oligo(p‐phenylene vinylene) Derivative with Five Emissive States

“…Because the emission characteristics of molecular materials can strongly depend on molecular conformation and electronic interactions between neighboring molecules, materials in which the molecular arrangement can be influenced by mechanical treatment are likely to display mechanoresponsive luminescent (MRL) behavior . This design approach permits creating MRL materials that can exhibit more than two emission colors ,. Indeed, several multicolored MRL materials have been reported based on this general strategy or a combination thereof with other approaches, such as the scission of covalent bonds .…”

Cyclophane‐Based Fluorescence Tuning Induced by Hydrostatic Pressure Changes

“…Mechanical stimuli can vary photoluminescence properties of organic materials in solution and/or solid states . Mechanoresponsive organic compounds are promising candidates of indicator of applied force, optical data storage and mechano‐bioimaging probes for living cells.…”

“…On the other hand, direct applications of mechanical stimuli to luminescent compounds as solid states have attracted much attention in a decade . Grinding, crushing and tensile deformation significantly affect the photophysical properties of molecular assembled materials .…”

Thermally activated delayed fluorescent phenothiazine–dibenzo[a,j]phenazine–phenothiazine triads exhibiting tricolor-changing mechanochromic luminescence

“…Therefore, the last 5 years have witnessed the emergence of multi-color-changing MCL materials. 6–8 In 2011, Kato pioneered distinct tricolor-switching MCL systems (green-yellow-red) comprising a single luminophore liquid-crystal by controlling complex self-assembled structures. 7 a Zou and Tian found that bis(pyridylvinyl)anthracene (BP2VA) significantly exhibits pressure-dependent luminochromism ranging from green to red.…”