A flexible molecular organic crystal with π–π bonding for the highly selective recognition of hydrogen isotopes†

Abstract

Deuterium oxide (D₂O) is widely used in diverse fields, notably as a moderator in heavy water reactors, for electrolytic extraction of deuterium gas, and in nuclear magnetic resonance (NMR) research. However, it exhibits a high susceptibility to H₂O contamination. Herein, a fluorescent hydrogen-bonded molecular organic crystal (ASP-101) with robust π–π interactions was synthesized by using 5,5′-(9,10-anthracene diphenyl dicarboxylic acid) (H₄ADIP) and dimethyl sulfoxide (DMSO). Distinct fluorescence quenching phenomena were observed when ASP-101 was soaked in H₂O and D₂O. Based on these phenomena, subsequent studies demonstrated that ASP-101 is capable of detecting trace amounts of H₂O in D₂O, with a K_SV value of 6 × 10⁻² M⁻¹ and a detection limit of 6.5 × 10⁻³ M (0.117 ppm). Batch experiments proved that the DMSO molecules within ASP-101 undergo exchange with H₂O and D₂O after soaking in aqueous solution. Previous research had found that deuteration can affect the emission properties of organic molecules. Thus, ASP-101's ability to detect H₂O in D₂O may be attributed to the fluorescent difference arising from the incorporation of H₂O and D₂O into its structure via solvent exchange. This study presents an authentic scenario for advancing isotopic identification based on alterations in fluorescence induced by solvent exchange.