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 π–π 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. [ABSTRACT FROM AUTHOR]