Effects of Gamma Radiation on Single- and Multicomponent Organic Crystalline Materials

Abstract

Exploration of highly ionizing radiation damage to organic materials has mainly been limited to polymers and single-component organic crystals due to their use in coatings and scintillation detection. Additional efforts are needed to create new tunable organic systems with stability in highly ionizing radiation to rationally design novel materials with controllable chemical and physical properties. Cocrystals are a promising class of compounds in this area because of the ability to rationally design bonding and molecular interactions that could lead to novel material properties. However, currently it is unclear if cocrystals exposed to radiation will maintain crystallinity, stability, and physical properties. Herein, we report the effects of γ radiation on both single-component- and multicrystalline organic materials. After irradiation with 11 kGy dose both single- (trans-stilbene, trans-1,2-bis(4-pyridyl)ethylene (4,4′-bpe), 1,n-diiodotetrafluorobenzene (1,n-C6I2F4), 1,n-dibromotetrafluorobenzene (1,n-C6Br2F4), 1,n-dihydroxybenzene (1,n-C6H6O2) (where n = 1, 2, or 3)), and multicomponent materials (4,4′-bpe)·(1,n-C6I2F4), (4,4′-bpe)·(1,n-C6Br2F4), and (4,4′-bpe)·(1,n-C6H6O2) were analyzed and compared to their preirradiated forms. Radiation damage was evaluated via single-crystal- and powder-X-ray diffraction, Raman spectroscopy, differential scanning calorimetry, and solid-state fluorimetry. Single-crystal X-ray diffraction analysis indicated minimal changes in the lattice postirradiation, but additional crystallinity changes for bulk materials were observed via powder X-ray diffraction. Overall, cocrystalline forms with 4,4′-bpe were more stable than the related single-component systems and were related to the relative stability of the individual conformers to γ radiation. Fluorescence signals were maintained for trans-stilbene and 4,4′-bpe, but quenching of the signal was observed for the cocrystalline forms to varying degrees. Three of the single components, 1,2-diiodotetrafluorobenzene (1,2-C6I2F4), 1,4-diiodotetrafluorobenzene (1,4-C6I2F4), and 1,4-dibromotetrafluorobenzene (1,4-C6Br2F4), also underwent sublimation within an hour of exposure to air postirradiation. Further analysis using differential scanning calorimetry (DSC) and Raman spectroscopy attributed this phenomenon to removal of impurities adsorbed to the crystal surface during irradiation.