Development of Stimuli-responsive Molecular Crystals Inspired by Known Molecular Scaffolds

This manuscript describes our strategy for developing stimuli-responsive molecular crystals through minimal transformations of known molecular skeletons. Rather than designing entirely new frameworks, we introduce small structural modifications to existing compounds and thereby create crystals showing new optical, mechanical, and phase-transition behaviors. In platinum isocyanide systems, arylation of halogenated precursors generates strongly emissive crystals with polymorphism, mechanochromism, crystal-to-amorphous transitions, and post-modification processes such as coproportionation and π-bridged dimerization. These examples show that simple molecular conversion can greatly expand crystal functionality. In benzodifuranone derivatives, bulky substituents suppress unfavorable face-to-face stacking and enable solid-state luminescence, mechanochromic responses, and thermosalient behavior. Furthermore, polymorphic benzodifuranone crystals exhibit photoregurated thermal phase transitions, leading to the unusual light-off salient effect, in which crystal motion occurs when irradiation is ceased. Overall, these studies demonstrate that organic synthesis can be used not only to make molecules, but also to design crystal packing, phase transitions, and macroscopic functions.