Robust Fluorescent Self-Assembly System for Sensing of Phosgene, Thionyl Chloride, and Oxalyl Chloride

A self-assembly fluorescent gelator (DIAN) based on a 3,4-diamine-naphthalimide derivative was constructed for sensing of multiple hazardous substances. The gelator DIAN self-assembled into organogels to form tightly packed nanofiber morphologies with hydrophobicity (water contact angles in the range of 130-146 degrees). DIAN responded to phosgene in a ratiometric mode, while it responded to thionyl chloride (SOCl2) and oxalyl chloride ((COCl)2) under the fluorescent "turn-off" mode. Results obtained from NMR and HRMS experiments demonstrated the sensing mechanism, and it was observed that phosgene, SOCl2, and (COCl)2 initially reacted with two amine groups of naphthalimide. The corresponding cyclization products were formed, and this induced the changes in fluorescence emission. Low limit of detection (LOD) values for phosgene, SOCl2, and (COCl)2 were recorded for DIAN in solution (LOD = 4.21, 1.98, and 1.29 nM) and xerogel films (LOD = 105, 69.1, and 33.3 ppb). The results reported herein can help provide a new platform for monitoring toxic phosgene, thionyl chloride, and oxalyl chloride.