Fluorescent Rotors Under Pressure

Our latest paper is out in JACS, describing the use of high-pressure crystallography and high-pressure optical spectroscopy to investigate how packing influences the optoelectronic properties of organic chromophores.

Thanks to our excellent collaborators Prof Stephen Moggach (Univeristy of Western Australia) and Prof Anita Jones (University of Edinburgh).

Abstract: To develop luminescent molecular materials with predictable and stimuli-responsive emission, it is necessary to correlate changes in their geometries, packing structures, and noncovalent interactions with the associated changes in their optical properties. Here, we demonstrate that high-pressure single-crystal X-ray diffraction can be combined with high-pressure UV–visible absorption and fluorescence emission spectroscopies to elucidate how subtle changes in structure influence optical outputs. A piezochromic aggregation-induced emitter, sym-heptaphenylcycloheptatriene (Ph7C7H), displays bathochromic shifts in its absorption and emission spectra at high pressure. Parallel X-ray measurements identify the pressure-induced changes in specific phenyl–phenyl interactions responsible for the piezochromism. Pairs of phenyl rings from neighboring molecules approach the geometry of a stable benzene dimer, while conformational changes alter intramolecular phenyl–phenyl interactions correlated with a relaxed excited state. This tandem crystallographic and spectroscopic analysis provides insights into how subtle structural changes relate to the photophysical properties of Ph7C7H and could be applied to a library of similar compounds to provide general structure–property relationships in fluorescent organic molecules with rotor-like geometries.