Mechano- and Photoresponsive Behavior of a Bis(cyanostyryl)benzene Fluorophore

Ryohei Kaneko; Yoshimitsu Sagara; Shouhei Katao; Nobuyuki Tamaoki; Christoph Weder; Hideyuki Nakano

doi:10.1002/chem.201900120

Mechano- and Photoresponsive Behavior of a Bis(cyanostyryl)benzene Fluorophore

Chemistry. 2019 Apr 26;25(24):6162-6169. doi: 10.1002/chem.201900120. Epub 2019 Apr 4.

Authors

Ryohei Kaneko¹, Yoshimitsu Sagara^{2

3}, Shouhei Katao⁴, Nobuyuki Tamaoki², Christoph Weder⁵, Hideyuki Nakano¹

Affiliations

¹ Department of Applied Chemistry, Muroran Institute of Technology, 27-1, Mizumoto-cho, Muroran, Hokkaido, 050-8585, Japan.
² Research Institute for Electronic Science, Hokkaido University, N20, W10, Kita-ku, Sapporo, Hokkaido, 001-0020, Japan.
³ JST-PRESTO, Honcho 4-1-8, Kawaguchi, Saitama, 332-0012, Japan.
⁴ Graduate School of Materials Sciences, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara, 630-0192, Japan.
⁵ Adolphe Merkle Institute, University of Fribourg, Chemin des Verdiers 4, 1700, Fribourg, Switzerland.

PMID: 30860632
DOI: 10.1002/chem.201900120

Abstract

The mechanoresponsive behavior and photochemical response of a new bis(cyanostyryl)benzene fluorophore (CSB-5) were investigated. Green fluorescence with λ_em,max of 507 nm was found for CSB-5 in chloroform solution, mirroring the behavior of a previously reported similar dye (CSB-6). Alternatively, crystalline samples of CSB-5 exhibited orange fluorescence with λ_em,max of 620 nm, attributable to excimer emission. Although the emission color change was not clearly noticeable by naked eye, CSB-5 exhibited mechanochromic luminescence, due to transformation into the amorphous state upon grinding the crystalline powder. Interestingly, rubbed films of CSB-5 prepared on glass substrates exhibited a pronounced emission color change from orange to green when exposed to UV light. This response is the result of a photochemical reaction that occurs in the amorphous state and which causes a decrease of the excimer emission sites so that the emission color changes from excimer to monomer. The crystalline material did not display such a photoinduced emission color change and the difference in photochemical reactivity between crystalline and amorphous states was exploited to pattern the emission color of rubbed films.

Keywords: bis(cyanostyryl)benzene analogue; emission color change; fluorescence; morphology; photochemistry.