Unlocking the sensing potential of phenyl-substituted perylene diimides under extreme conditions

Phenyl-substituted perylene diimide (PTCDI-Ph) derivatives are prospective organic, electronic and optoelectronic materials. In this study, the effects of modified intermolecular interactions and molecular conformations on the energy gap and the optical properties of PTCDI-Ph were explored at high pressure and various temperatures by calorimetry, X-ray diffraction, UV-vis absorption, and photoluminescence spectroscopy. Below 498 K, PTCDI-Ph transforms from phase I to phase II, which is stable down to 93 K at least. Above 3.0 GPa, phase II transforms into phase III. The compressed intermolecular distance between perylene cores linearly narrows the band gap, due to the intensified & pi;-& pi; stacking. The negative linear compressibility of the crystal along [100] coincides with the negative thermal expansion in this direction. Owing to the strong pressure and temperature dependence of the luminescence spectrum, the PTCDI-Ph derivatives constitute a promising class of highly stimuli-responsive elastic organic materials with broad potential for tailoring their optoelectronic properties through physical and chemical modifications.