A new series of N-P[double bond, length as m-dash]Se resonance-based fluorescent molecules were developed and used for the detection of hypochlorous acid (HClO) with rapid response and high selectivity. These Se-containing molecules can selectively detect trace amounts of HClO in nM, showing significantly strengthened fluorescence due to the enhanced resonance variation with an increased distance between the fluorophore and Se. The design of N-P[double bond, length as m-dash]Se resonance molecules in donor-resonance-acceptor (D-r-A) architectures could be an important way to develop high-performance turn-on fluorescent probes for HClO detection.