Fluorescent organic single crystals with elastic bending flexibility: 1,4-bis(thien-2-yl)-2,3,5,6-tetrafluorobenzene derivatives

Shotaro Hayashi,Atsushi Asano,Takuto Maeda,Yoshinobu Yokomori,Natsumi Kamiya,Toshio Koizumi

doi:10.1038/s41598-017-09848-0

Shotaro Hayashi, Atsushi Asano + Show 4 more

Open Access

https://doi.org/10.1038/s41598-017-09848-0

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Journal: Scientific Reports	Publication Date: Aug 25, 2017
Citations: 62	License type: open-access

Affiliation: National Defense Academy of Japan

Abstract

Organic single crystals with elastic bending flexibility are rare because they are generally brittle. We report here fluorescent organic single crystals based on thiophene-tetrafluorobenzene-thiophene derivatives, mainly 1,4-bis(thien-2-yl)-2,3,5,6-tetrafluorobenzene. Three derivatives were synthesized by Pd-catalyzed cross-coupling reactions (Stille or direct arylation pathways). The crystallization of the derivatives gave large (mm- or cm-scale) crystals. Two crystals of 1,4-bis(thien-2-yl)-2,3,5,6-tetrafluorobenzene, 1, and 1,4-bis(4-methylthien-2-yl)-2,3,5,6-tetrafluorobenzene, 3, bent under applied stress and quickly recovered its original shape upon relaxation. The other crystal of 1,4-bis(5-methylthien-2-yl)-2,3,5,6-tetrafluorobenzene, 2, showed brittle breakage under applied stress (normal behavior). Fibril lamella crystal structure based on criss-cross packed slip-stacked molecular wires and its structural integrity are important factors for the design and production of next generation crystal materials with elastic bending flexibility. Furthermore, mechanical bending–relaxation resulted in reversible change of the morphology and fluorescence (mechanofluorochromism). Such bendable crystals would lead to the next generation solid-state fluorescent and/or semiconducting materials.

Highlights

Elastic materials such as rubbers, which are able to largely and reversibly deform, exhibit entropic elasticity and are termed as elastomers[1,2,3]
The fibril lamella crystal structure originates from the slip-stacked molecular wires at the (010) and (001) faces (Fig. 3C) through self-assembly of planar thiophene– tetrafluorophenylene–thiophene molecules
The crystal structure of 3 featured S–F (2.719 Å) and F–H (2.218 Å) intramolecular contacts that were significantly shorter than the sums of their van der Waals radii [(dSF = rS + rF = 3.27 Å); www.nature.com/scientificreports/

Summary

Introduction

Elastic materials such as rubbers, which are able to largely and reversibly deform, exhibit entropic elasticity and are termed as elastomers[1,2,3]. We have succeeded in obtaining the elastic organic single crystal of a fluorescent π-conjugated molecule, 3 (Fig. 1)[10]. The fibril lamella crystal structure originates from the slip-stacked molecular wires at the (010) and (001) faces (Fig. 3C) through self-assembly of planar thiophene– tetrafluorophenylene–thiophene molecules.

Results

Conclusion