Macrocycle-based supramolecular assembly: An alternative strategy for visualizing the mechanism of piezochromic luminescence

Abstract

Though clarifying the relationship between packing and emission is very important and highly desirable for understanding the mechanism behind responsive luminescent materials, it is not an easy case for piezochromic luminescent materials, due to the difficulties of in situ tracking the interactions change during pressurization. Herein, a smart supramolecular assembly strategy based on two macrocyclic hosts with tailored guests’ packing has been proposed for illustrating the mechanism of piezochromic luminescence. The elusive changes of molecular packing associated with variable luminescence behavior under mechanical forces, such as grinding and high pressure, can be expressed intuitively by cryptand (CP) or cucurbit [7]urils (CB [7])-based host-guest complex in a visualized way. Specifically, the enhanced π-π stacking interactions induced by CP corresponds well to the dim and red-shifted emission under isotropic compression, while the isolated chromophore in non-aromatic CB [7] with reduced intermolecular π-π interactions perfectly explains the brightened and blue-shifted emission after grinding. This controllable self-assembly strategy provides a reliable and smart strategy for visualizing the mechanism of piezochromic luminescence.