A Screening Approach for the Discovery of Mechanochromic Gold(I) Isocyanide Complexes with Crystal-to-Crystal Phase Transitions

• Published in: Journal of the American Chemical Society 2016-05, Vol.138 (19), p.6252-6260
• Main Authors: Seki, Tomohiro, Takamatsu, Yuki, Ito, Hajime
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.6b02409

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 R 1 –R 2 (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 R 1 –R 2 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 R 1 –R 2 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 CF 3 –CN complex were obtained. Density functional theory calculations indicated that the mechanoinduced red-shifted emission of CF 3 –CN is caused by formation of aurophilic interactions. Comparison of the crystal structures of CF 3 –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.