Piezochromic Luminescence of Pyrene Derivatives Polymorphism Around Excimer Forming Process

Pyrene aggregates, as classic luminescent materials, are of great interest from a scientific viewpoint owing to the development of optoelectronic materials. In this study, we designed a compound 1,4,5-triphenyl-2-(pyren-1-yl)-4,5-dihydro-1H-imidazole (IM-PY) which was achieved with two crystalline polymorphs (IMPY-G and IMPY-B). They exhibit the green emission and the blue emission, respectively, both with pyrene serving as the luminescent core. At ambient conditions, both phases exhibit π-π pyrene dimer stacking, but IMPY-B has the obviously smaller overlapping area and slightly shorter distance of pyrene planes than IMPY-G. During compression, the experiment results of photoluminescence, in situ UV-vis absorption, time-resolved emission, and synchrotron angular dispersive X-ray diffraction, combined with theoretical calculations indicate that IMPY-B shows a more pronounced red-shifted photoluminescence spectra and forms excimers at higher pressure than IMPY-G. This fully reflects the influence of different stacking structures on the piezochromic phenomenon of aggregates, which is beneficial for expanding the application of pyrene aggregated state.