Controlling the Emergence and Shift Direction of Mechanochromic Luminescence Color of a Pyridine‐Terminated Compound

Abstract

In this study,m echanochromicl uminescencew as induced in acomplex of mechano-inactive compounds. Dye/ acid complexes containing the same p-conjugated backbones were prepared. While the luminophores howedb lue and red shifts in photoluminescence spectra when combined with different acids by grinding, it exhibited slightmechanoresponsiveness itself. Also, compounds with similar molecular backbones to the dye/acid complex were synthesized to clarify the colorc hange mechanism.T he compounds showed both blue and red shifts in photolumines-cence and diffuse reflectance spectra upon grinding, indicating that mechanochromic luminescence in the hydrogenbondedcomplexi slike its monomeric analogue and that aggregations tructure plays an important role in mechanoresponsiveb ehaviorr ather than the p-conjugated structure. It was shown that acolor change can be mechanically induced by imitating the solid-state aggregation structure of other mechanoresponsive compounds without synthetic modification.[a] Dr.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.Recently,C hujo and co-workersd emonstrated switching of the directiono ft he peak shifts of the emission bands by varying the degree of sterich indranceo ft he end group. [14] This result suggested that the MCL behavior enabled switching of the peak shift direction by changing the substituent. Additionally, the hydrogen-bondedM CL complex enabled change in the substituent by changingt he acid species with different chemical structures.H erein, an ovel pyridine-terminated fluorescent dye (luminophore) MX (Figure 1a)i sd escribed, which shows MCL when combined with an acid. Furthermore, the dye showedb oth blue and red shiftc hanges in PL color upon mechanical grinding with different acid species.

Blue-Shifting Mechanofluorochromic Luminescent Behavior of Polymer Composite Films Using Gelable Mechanoresponsive Compound

“…By combining these properties with the functions of MCL, it is possible to develop special MCL materials that exhibit multicolor emission [12][13][14], circularly polarized PL [15], and anisotropy. Previously, we studied MCL materials based on liquid crystalline cyanostilbenes and detected the grinding direction using the stress orientation of LCs [16,17] and emission color control using supramolecular LC complexes [18,19]. Recently, rod-shaped tolane-terminated cyanostilbene was prepared, and its mechanoresponsive change in luminescent behavior was evaluated.…”

Mechanochromic luminogens with hypsochromically shifted emission switching property: recent advances and perspectives

“…On the other hand, blue-shifted emission switching is most of the times serendipitously obtained and hence is rarely reported. [87][88][89][90][91] Since the number of MLs that show blue shifted emission in response to mechanical stimuli are limited, the underlying mechanism behind the mechanical stimuli induced blue-shifted emission switching is often unclear. Researchers are trying to know the exact underlying mechanism behind the grinding induced blue shift of MLs because the knowledge about the mechanism of emission wavelength switching could further allow manipulation of the molecular structure and packing modes of a mechanochromic luminogen to attain desired tunable emissions.…”

Recent Advances in Mechanochromic Luminescence of Organic Crystalline Compounds

“…Kondo, Kawatsuki, and coworkers also reported the MCL of acid-base complexes composed of pyridine-substituted fluorophore and benzoic acid derivatives. 58 In 2018, Chen, Wang, and coworkers utilized intramolecular B/N Lewis pairs with a flexible framework to achieve multistimuli-responsive luminescent switching in crystalline state. 59 Crystalline samples of B/N Lewis-paired compound 28 exhibited typical MCL between blue and green (Figure 7f ).…”