Force-triggered hypso- and bathochromic bidirectional fluorescence switching beyond 120 nm and its anticounterfeiting applications

Abstract

Achieving high-contrast tricolor emissive regulation of a single-component molecule using a single type of external stimulus is highly desirable but challenging. In the present study, we report a symmetric acceptor-donor-acceptor (A-D-A)–type aggregation-induced emission-active luminogen, which displays a sequential high-contrast fluorescence switching just by anisotropic mechanical grinding. Specifically, upon light grinding, an orange–yellow-to-blue hypsochromic mechanofluorochromic response with a distinct color contrast (change in the maximum emission wavelength, Δλ em,max = 122 nm) is noticed, and the slightly ground solid exhibits a blue-to-red high-contrast (Δλ em,max = 185 nm) bathochromic mechanofluorochromic conversion upon vigorous grinding. Thus, using a single luminogen developed here, we can realize wide-range (Δλ em,max > 100 nm) hypso- and bathochromic fluorescence mechanochromisms simultaneously. The tricolored mechanofluorochromic phenomenon is attributed to two different morphological transitions involving crystalline-to-crystalline and crystalline-to-amorphous states. Furthermore, three information anticounterfeiting systems are developed using the luminogen presented here.

On Sense and Deform: Molecular Luminescence for Mechanoscience

“…(b–c) Schematics of (b) molecular shapes (inset shows an example of a combined system) and (c) packing motifs (colored blocks represent discrete molecules). (d) Representative MRL patterns (dotted and solid arrows represent crushing and grinding processes, respectively) and corresponding images under UV irradiation (reproduced from ref /ref /ref , copyright 2009/2014/2016 American Chemical Society; reproduced with permission from ref , copyright 2024 American Association for the Advancement of Science; ref , copyright 2020 The Royal Society of Chemistry; ref /ref , copyright 2012/2015 John Wiley & Sons, Inc. See Figure for chemical structures and Δλ MRL ranges. ).…”

“…Similarly, phenanthroimidazolylbenzothiadiazoles exhibited disrupted and enhanced intermolecular CT transitions upon fracturing/sonication and grinding. 119 Recently, Chen and Sun demonstrated the widerange hypso-and bathochromic MRL (Δλ MRL = −122 and +185 nm, respectively) by integrating semilocked TPE, TPA, and BTF motifs (Sym-ADA, Figures 2d-iii and 3), 110 which was driven by sandwich-to-herringbone conformation change and excimer formation in the amorphous phase upon gentle and vigorous grinding, respectively. The bidirectional shifts of the fluorescence spectra were also observed in the mechanically and thermally produced "amorphous" forms (ground and molten states, respectively) of acetyl pyrenes and pyrenyl ynones.…”