Anisotropic Thermal Expansion as the Source of Macroscopic and Molecular Scale Motion in Phosphorescent Amphidynamic Crystals

Abstract

The structural origin of multiscale phenomena, with physical manifestations ranging from the molecular to the macroscopic scale, remains largely undocumented. Here we report the discovery of a crystalline molecular rotor with rotationally‐modulated triplet emission that displays macroscopic dynamics in the form of crystal moving and/or jumping, also known as salient effects. Crystals of molecular rotor 2 with a central 1,4‐diethynyl‐2,3‐difluorophenylene rotator linked to two gold(I) nodes, which crystalizes as infinite 1D chains by taking advantage of intermolecular gold(I)‐gold(I) interactions. It was shown that rotational motion leads to changes in the orientation of the central phenylene, causing changes in electronic communication between adjacent chromophores, which are manifested as changes in emission intensities. Crystals of 2 showed the large and reversible thermal expansion/compression anisotropy, which was shown to account for (1) a nonlinear Arrhenius behavior in molecular‐level rotational dynamics, which correlates with (2) changes in emission, and determines (3) the macroscopic crystal motion. Furthermore, a molecular rotor analog 3 possessing a 1,4‐diethynyl‐2,3,5,6‐tetrafluorophenylene rotator exhibited unit cell anisotropy, crystal dynamics, emission properties and thermosalience that are similar to those of 2 , suggesting potentially generalizable new avenues to control mechanical properties at the molecular and macroscopic scales.