Division of Applied Chemistry
and Frontier Chemistry Center (FCC), Faculty
of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan
and Frontier Chemistry Center (FCC), Faculty
of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan
J. Am. Chem. Soc., 2016, 138 (19), pp 6252–6260
DOI: 10.1021/jacs.6b02409
Publication Date (Web): April 12, 2016
Copyright © 2016 American Chemical Society
ACS Editors' Choice - This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.
Abstract
Mechanoinduced
phase transitions of emissive organic crystalline materials have
received much attention. Although a variety of such luminescent
mechanochromic compounds have been reported, it is challenging to
develop mechanochromic compounds with crystal-to-crystal phase
transitions in which precise structural information about molecular
arrangements can be obtained. Here, we report a screening approach to
explore mechanochromic compounds exhibiting a crystal-to-crystal phase
transition. We prepared 48 para-substituted (R1) phenyl[para-substituted (R2) phenyl isocyanide]gold(I) complexes designated R1–R2 (six R1 and eight R2
substituents) and then performed three-step screening experiments. The
first screening step was selection of emissive complexes under UV light,
which gave 37 emissive R1–R2
complexes. The second screening step involved evaluation of the
mechanochromic properties by emission spectroscopy. Twenty-eight
complexes were found to be mechanochromic. The third screening step
involved preparation of single crystals, reprecipitated powders, and
ground powders of the 28 mechanochromic R1–R2
complexes. The changes in the powder diffraction patterns of these
complexes induced by mechanical stimulation were investigated. Two
compounds exhibited a crystal-to-crystal phase transition upon
mechanical stimulation, including the previously reported H–H complex. Single crystals of the as-prepared and ground forms of the newly discovered CF3–CN complex were obtained. Density functional theory calculations indicated that the mechanoinduced red-shifted emission of CF3–CN is caused by formation of aurophilic interactions. Comparison of the crystal structures of CF3–CN
with those of the other complexes suggests that the weaker
intermolecular interactions in the as-prepared form are an important
structural factor for the observed mechanoinduced crystal-to-crystal
phase transition.
phase transitions of emissive organic crystalline materials have
received much attention. Although a variety of such luminescent
mechanochromic compounds have been reported, it is challenging to
develop mechanochromic compounds with crystal-to-crystal phase
transitions in which precise structural information about molecular
arrangements can be obtained. Here, we report a screening approach to
explore mechanochromic compounds exhibiting a crystal-to-crystal phase
transition. We prepared 48 para-substituted (R1) phenyl[para-substituted (R2) phenyl isocyanide]gold(I) complexes designated R1–R2 (six R1 and eight R2
substituents) and then performed three-step screening experiments. The
first screening step was selection of emissive complexes under UV light,
which gave 37 emissive R1–R2
complexes. The second screening step involved evaluation of the
mechanochromic properties by emission spectroscopy. Twenty-eight
complexes were found to be mechanochromic. The third screening step
involved preparation of single crystals, reprecipitated powders, and
ground powders of the 28 mechanochromic R1–R2
complexes. The changes in the powder diffraction patterns of these
complexes induced by mechanical stimulation were investigated. Two
compounds exhibited a crystal-to-crystal phase transition upon
mechanical stimulation, including the previously reported H–H complex. Single crystals of the as-prepared and ground forms of the newly discovered CF3–CN complex were obtained. Density functional theory calculations indicated that the mechanoinduced red-shifted emission of CF3–CN is caused by formation of aurophilic interactions. Comparison of the crystal structures of CF3–CN
with those of the other complexes suggests that the weaker
intermolecular interactions in the as-prepared form are an important
structural factor for the observed mechanoinduced crystal-to-crystal
phase transition.
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