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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]

Flexible and transformable molecules, particularly those responding to external stimuli, are needed for designing sensors and porous compounds capable of storing or separating gases and liquids. Under normal conditions the photochromic compound, 1,2-bis[2-methyl-5-(pyridyl)-3thienyl]cyclopentene (BTCP) forms a porous co-crystal with 1,4-diiodotetrafluorobenzene (dItFB). It traps acetone (Ac) molecules in the pores. Owing to a unique system of pores in the polar framework, the crystal is sensitive to the humidity in the air and to the chosen liquid environment. When compressed in non-penetrating media, the crystal displays a strong negative linear compressibility (NLC) along [100]. [ABSTRACT FROM AUTHOR]