Piezochromic Luminescence of Pyrene Derivatives Polymorphism around Excimer Forming Processs

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.