Binaphthol diimide scintillators for X-ray imaging

Rylene diimides are an attractive class of organic dyes owing to their exceptional optical properties and optoelectronic applications. Herein, we extend their applications to the realm of X-ray imaging. The emissive 1,1′-bi(2-naphthol-4,5-dicarboximide) (BiND-OH) and its phenyl/methyl derivatives, BiND-OPh and BiND-OMe, have been selected to investigate the structure-activity relationships between their crystal packing and X-ray scintillation properties. Single crystal X-ray diffraction results indicate that BiND-OH forms a tightly structured conformation with two interlocks by hydrogen bonding, leading to a charge transfer state and resulting in nearly non-scintillation. In contrast, the radioluminescence intensities of BiND-OPh and BiND-OMe have increased by about 73 and 537 times, respectively, owing to the disruption of hydrogen bonding control and the formation of a J-aggregation fraction dominated by π-π interactions. Remarkably, BiND-OMe displays superior scintillation properties, marked by reduced non-radiative transitions, attributed to greater π-π plane distances, extended slip distances, and diminished π-plane overlap areas. It demonstrates a low detection limit of 70.68 nGy s⁻¹ and a short decay time of 4.37 ns. When applied to X-ray imaging, it produces a high spatial resolution of 11.0 lp mm⁻¹. This finding provides valuable insights into the profound impact of molecular structure and aggregation state on the organic scintillation properties.