Mechanofluorochromic Material toward a Recoverable Microscale Force Sensor

Abstract

cation of mechanical stimuli such as scratching or grinding, promises applications for force sensors. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] Emission changes of coordination complex crystals, [24] polymeric microcrystals, [30] and organic fluorophores, [31][32][33][34][35][36] have been correlated to an applied force or pressure for new anticounterfeiting technologies [23][24][25][26][27][28] and biological stress probes. [29] Force sensing via mechanofluorochromic activity has been reported at the micro/nanoscales by direct measurement of emission changes upon in situ application of varying amounts of mechanical stimulus. [24,30,31,[33][34][35][36] Yet, one issue that remains to be explored is the recovery of the material. Emission changes, correlated with applied force, are induced by morphological changes in the material. This means that subsequent sensing events, after the initial application of force, necessitate recovering the original morphology-a process not so straightforward as this usually requires thermal annealing, [38] solvent fuming, [25,27] or recrystallization. [20][21][22]37] Self-recovery, the spontaneous return to the initial state (of absorption, emission and morphology) of the scratched/ground material under ambient conditions, has been observed in derivatives based on Au(I) complexes, [28] pyrene, [39,40] anthracene, [41,42] tetraphenylethene, [43,44] indolylbenzothiadiazole, [45] triphenylamine, [46] boron-coordinated β-diketonate complexes, [47] and hexathiobenzene. [48] However, many MFC-active materials are left unexplored for multiple-use force sensing applications, not only due to the complexity of instrumentation required for such studies, [24,30,31,[33][34][35][36] but also due to the lack of molecular design leading to reversibility [40] and a clear understanding of mechanism of self-recovery. [30,45] Recently, mechanofluorochromic films based on a family of diphenylamine compounds functionalized with π-extended

Mechanofluorochromic behaviours of functionalized carbazole‐based difluoroboron compounds with different aryl substituents moieties

“…Among many luminescent molecules [1–4], organic materials with mechanofluorochromic (MFC) behaviours have attracted numerous interest [5–10] because of their unique potential applications in fields of organic light‐emitting diodes [11], security papers [12], mechano‐sensors [13], and memory devices [14]. To date, a great amount of effort has been devoted to the design and synthesis of materials with MFC characteristics, including the derivatives of isoquinoline [15], tetraphenylethylene [16], carbon nanodots [17], 9,10‐distyrylanthracene [18], azaanthracence [19], naphthalimides [20] and some organic boron‐containing π‐conjugated molecules [7, 9].…”

On Sense and Deform: Molecular Luminescence for Mechanoscience

“…Furthermore, the contact force between a cantilever and the surface of a material has enabled the quantitative indenting and scratching of MRL-active molecular microcrystals. Confocal fluorescence microscopy has also facilitated the correlation of the topography of scratched surfaces with the corresponding emission spectra at a sub-μm scale. − In 2000, Burns et al first demonstrated the nanoscale shear-induced blue-to-red chromatic transition (red form is also weakly fluorescent) of a polydiacetylene thin film using the AFM tip …”

Optical Phenomena in Molecule-Based Magnetic Materials

“…192 Thus, they take advantage of the switching of light emission by external stimuli, e.g., solvent molecules (solvatofluorochromism, often called solvatochromic luminescence), 193 temperature (thermofluorochromism), 194 electric field (electrofluorochromism), 195 pressure (piezofluorochromism), 196 or mechanical action (mechanofluorochromism). 197 Photochromic luminescence was also realized; in this case, as the light irradiation can be used both as a trigger to switch the state of a material and as the generator of the output signal; thus, to employ such luminescent photochromism in optical devices, the usage of two different wavelengths playing two above-mentioned roles is the most convenient, yet challenging, solution. 198,199 The broad research area within optical materials is also occupied by the materials able to exhibit various nonlinear optical (NLO) properties such as two-photon absorption, second and higher-order harmonic generation (SHG and others), or the optical Kerr effect.…”

“…In this regard, the stimuli-responsive luminescent materials are the emissive analogs of chromic materials, often named fluorochromic systems . Thus, they take advantage of the switching of light emission by external stimuli, e.g., solvent molecules (solvatofluoro­chromism, often called solvatochromic luminescence), temperature (thermofluoro­chromism), electric field (electrofluoro­chromism), pressure (piezofluoro-chromism), or mechanical action (mechanofluoro­chromism) . Photochromic luminescence was also realized; in this case, as the light irradiation can be used both as a trigger to switch the state of a material and as the generator of the output signal; thus, to employ such luminescent photochromism in optical devices, the usage of two different wavelengths playing two above-mentioned roles is the most convenient, yet challenging, solution. , …”