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

Abstract

Herein we report 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. Molecular rotor 2 with a central 1,4-diethynyl-2,3-difluorophenylene rotator linked to two gold(I) nodes, crystalizes as infinite 1D chains through intermolecular gold(I)-gold(I) interactions. The rotational motion changes the orientation of the central phenylene, changing the electronic communication between adjacent chromophores, and thus the emission intensities. Crystals of 2 showed the large and reversible thermal expansion/compression anisotropy, which accounts 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. A molecular rotor analogue 3 has properties similar to those of 2, suggesting a generalized way to control mechanical properties at molecular and macroscopic scales.