Coumarin-Based Fluorescent Probe for the Detection of N-methyl-p-nitroaniline in Propellant Aging

Rocket propellant aging significantly affects the safety and service life of energetic materials, so accurate aging evaluation is indispensable for the full life cycle health management of propellants. However, conventional aging assessment depends on the indirect detection of gaseous byproducts such as NO and NO₂, which suffers from inherent signal hysteresis and environmental interference. To overcome these limitations, a ratiometric fluorescent sensing platform based on 7-hydroxycoumarin (7-HC) was developed for the direct and specific detection of N-methyl-p-nitroaniline (p-MNA). The presence of p-MNA triggers effective fluorescence quenching of 7-HC based on the inner filter effect with dual emission peaks at 373 and 445 nm, and the ratiometric sensing strategy efficiently eliminates complex matrix disturbances and instrumental errors, significantly improving detection accuracy and anti-interference capability. Experimental results show that the 7-HC probe exhibits a rapid response within 20 s and excellent selectivity toward p-MNA against various common interferents. Furthermore, 7-HC-doped KBr pellets enable solid-state visual detection of p-MNA. Notably, the proposed strategy can distinguish propellant samples with different aging degrees at both solution and film levels. This work establishes a method for direct p-MNA detection in propellants, providing a promising technical route for aging state evaluation and safety monitoring of energetic materials.