Mechanically-Sensitive Fluorochromism by Molecular Domino Transformation in a Schiff Base Crystal

The ability to make large changes in properties against small external stimuli is one of key factors in sensing materials. Molecular domino transformation, i.e. polymorphic transformation starting at a stimulated point and extending to the whole crystal, is an attractive phenomenon from this viewpoint. We recently found such a transformation in a crystal of 4-nitro-N-salicylideneaniline as one of Schiff bases. In this study, quantitative evaluations were conducted on a mechanical stimulus and emission properties in the transformation of the crystal. Our results demonstrate the potential applicability of the crystal to detection of even less than a few μN mechanical stimuli as an emission color change. A molecular level transformation mechanism revealed by microcrystal electron diffraction also contributes to future development of the transformation-based materials.