Effect of sensing material basicity on excited-state intramolecular proton transfer-based detection of G-series nerve agents

The use of G-series nerve agents represents a significant threat and there is a need for rapid and selective in-field identification. We report that sensing materials composed of ESIPT-based silyl ethers can be used to detect the hydrogen fluoride that is present in phosphonofluoridate agents such as sarin and its simulant di- iso -propyl fluorophosphate (DFP). We find that the ability of the sensing material to detect the hydrogen fluoride in DFP is dependent on the basicity of the nitrogen atom that forms part of the ESIPT moiety upon deprotection. When the pKa of the conjugate acid of the nitrogen atom was lower than that of hydrogen fluoride the ability of the sensing material to detect the acid and hence simulant was curtailed. However, when the pKa of the conjugate acid was 3 or higher, then hydrogen fluoride could be rapidly detected. The best performing sensing material could detect hydrogen fluoride concentrations as low as 3 ppb in DFP of 99 % purity in one minute. Based on sarin having the same purity level, we estimate that it would be detectable at a concentration of ≈40 ppb in one minute, which is lower than the Acute Exposure Guideline 3 (life-threatening effects) of 64 ppb for a 10-min exposure. • Silylated ESIPT sensing materials can detect phosphonofluoridate nerve agents. • De-silylation by hydrogen fluoride (HF) leads to ESIPT emission being turned on. • The ability to detect the HF is dependent on the basicity of the ESIPT moiety. • Sarin is estimated to be detectable at a concentration of ≈40 ppb in one minute.