Visualizing changes of molecular conformation in the solid-state by a common structural determination technique: single crystal X-ray diffraction

Changes of molecular conformation in the solid state play a vital role in many advanced technologies. Single-crystal X-ray diffraction (XRD), serving as a common structural determination technique, has been widely used to perform structural analysis. In this work, variable-temperature XRD characterization has been utilized to "see" the static conformational change (SCC) and dynamic trajectory (DT) of tetraphenylethylene (TPE) in the solid state, which exhibits an aggregation-induced emission (AIE) effect. Five kinds of motions, stretching, torsion, twisting, rocking, and wagging, are observed and analyzed. In terms of the SCC, the middle double bond in TPE becomes short and twisted and the peripheral phenyl rings as a whole tend to be more twisted with increase of the testing temperature (150 to 298 K). For the DT, phenyl-ring rocking and wagging are found to be more and more vigorous along with the increase of temperature, which is closely related to the synchronously decreased luminescent intensity. This work affords direct structural evidence for the AIE mechanism of restriction of intramolecular motions and provides a new platform to investigate the photophysical processes.