An 8-hydroxyjulolidine-phenanthroline dyad as a chemodosimeter for nerve agent mimic DCP: Sensing performance and potential applications

Two new fluorescent Schiff base compounds (JP-1 and JP-2) were synthesized via the condensation reaction between 1,10-phenanthroline-5-amine and 8-hydroxyjulolidine-9-carboxaldehyde, and subsequently characterized using various techniques. The photophysical properties of JP-1 and JP-2 were analyzed. While JP-1 showed no sensing capability due to the lack of hydroxyl group, JP-2 selectively detected diethylchlorophosphate (DCP)-a sarin gas analogue-in both the solution and gas phases. In acetonitrile, JP-2 sensed DCP via a distinct colorimetric change from light yellow to pale orange and a ratiometric fluorescence red-shift from green (495 nm) to orange (575 nm). The probe exhibited a low detection limit of and an apparent binding constant of 1.44 × 10⁶ M^-1. Mechanistic insights from ¹H NMR titrations, ESI-MS, and TD-DFT calculations revealed that DCP interacts with the hydroxyl group, releasing HCl. The free probe JP-2 exhibits an enhanced spectral response at 495 nm attributed to strong ESIPT and weak ICT photophysical mechanism. The interaction with DCP and simultaneous protonation of HCl at the nitrogen of phenanthroline results in significant ICT and disruption of ESIPT, causing a ratiometric red shift at 575 nm. Introducing triethylamine (TEA) deprotonated the phenanthroline nitrogen and restored the 495 nm response, demonstrating single-cycle optical reversibility. Finally, JP-2 successfully detected DCP in soil samples and via bio-imaging in Danio rerio gill (DrG) cells, highlighting its practical utility for environmental monitoring and biological assays.