Exploring Confinement-Induced Self-Assembly of Anthracene in a Janus Inorganic Nanotube as a Route to Water-Dispersible Nanoscintillators

Developing scintillators that are water-dispersible, easily processable, environmentally benign, and compatible with polymer or glass matrices is an important requirement in advancing materials for photodynamic therapy and fabricating miniaturized radiation detection devices. Herein, we demonstrate the self-assembly-driven formation of anthracene nanocrystals within Janus, water dispersible, and optically transparent methyl imogolite nanotubes (Imo-CH3 NTs) accompanied by confinement-induced changes in its UV-vis absorption and fluorescence response. From combined SAXS, XRD, FTIR, and UV-vis analysis, it is inferred that the one-dimensional confinement environment of the nanotube compels the encapsulated anthracene molecules into a restricted arrangement adopting a distinct nanocrystalline ordering correlating with a reduced optical band gap of 2.91 eV, promoting coherent π-π interactions, impacting electronic excitation due to the restriction of intramolecular vibrations and excitonic coupling along the encapsulation axis. The fluorescence of anthracene initially quenches with Imo-CH3 encapsulation, but the formation of molecular nanocrystal at the increased loading concentration restricts the intramolecular motions, thereby decreasing the nonradiative relaxation pathways and enhancing the radiative emission leading to partial restoration of the fluorescence. This behavior along with the change in fluorescence lifetime is consistent with the signs of ordering and is reflected in a modest scintillation response under energetic (α-particle) excitation. While the observed scintillation response needs further improvement, the retention of the scintillation characteristics in a water-dispersible nanosystem signifies an important development with respect to conventional organic scintillators, which typically require bulk crystalline or hydrophobic solvent environments posing challenges in terms of cost and scalability.