Regulation of Multicolor Fluorescence Changes Found in Donor‐acceptor‐type Mechanochromic Fluorescent Dyes

• Published in: Chemistry, an Asian journal Vol. 16; no. 15; pp. 2136 - 2145
• Main Authors: Ishi‐i, Tsutomu, Tanaka, Honoka, Kichise, Rihoko, Davin, Christopher, Matsuda, Takaaki, Aizawa, Naoya, Park, In Seob, Yasuda, Takuma, Matsumoto, Taisuke
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 02.08.2021
• Subjects: benzothiadiazoles; Chemistry; Color; Crystal structure; donor-acceptor; Fluorescence; Fluorescent dyes; Fluorine; Functional groups; Grinding; mechanochromic fluorescence; Mechanoluminescence; multicolor fluorescence; triphenylamines
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.202100538

The regulation of multicolor fluorescence changes in mechanochromic fluorescence (MCF) remains a challenging task. Herein, we report the regulation of MCF using a donor‐acceptor structure. Two crystal polymorphs, BTD‐pCHO(O) and BTD‐pCHO(R) produced by the introduction of formyl groups to an MCF dye, respond to a mechanical stimulus, allowing a three‐color fluorescence change. Specifically, the orange‐colored fluorescence of the metastable BTD‐pCHO(O) polymorph changed to a deep‐red color in the amorphous‐like state to finally give a red color in the stable BTD‐pCHO(R) polymorph. This change occurred by mechanical grinding followed by vapor fuming. The two different crystal packing patterns were selectively regulated by the electronic effect of the introduced functional groups. The two types of selectively formed crystals in BTD(F)‐pCHO bearing fluorine atoms, and BTD(OMe)‐pCHO bearing methoxy groups, respond to mechanical grinding, allowing for the regulation of multicolor MCL from a three‐color change to two different types of two‐color changes. Two types of crystals of donor‐acceptor‐type dyes are selectively constructed by the electronic effects of the functional groups introduced to their acceptor moieties. The crystals respond to mechanical grinding to give regulatable multicolor mechanochromic fluorescence. The fluorescence could be altered from a three‐color change to two different two‐color changes.