To gain more insights into the chemical sensing behaviors of JUC-557-nanosheet, we also explored their potential in molecular recognition of nitro-compounds, which is of great importance for environmental concerns, homeland security and anti-terrorism measures. Herein, five important nitro-compounds were chosen as model detected molecules, including nitrobenzene (NB), o-dinitrobenzene (o-DNB), mdinitrobenzene (m-DNB), p-dinitrobenzene (p-DNB), and 1,3,5-trinitrotoluene (TNT). Among them, TNT is a typical explosive, and others are classified as volatile carcinogens. Remarkably, compared with o-DNB (11.2%), m-DNB (12.7%), and p-DNB (18.6%), the fluorescence quenching percentages of JUC-557-nanosheet for NB and TNT were much higher, up to 98% and 85.1% respectively (Fig. and Supplementary Figs. ). Furthermore, the K a values were calculated to be 6.18 × 10 6 M -1 for NB (R 2 = 0.99) and 4.38 × 10 5 M -1 for TNT (R 2 = 0.99), while the K a values of JUC-557-nanosheet for other nitro-compounds were much lower (only 5.27 × 10 3 M -1 for o-DNB, 3.31 × 10 3 M -1 for m-DNB and 1.35 × 10 4 M -1 for p-DNB, Supplementary Figs. 76-78), indicating that JUC-557-nanosheet displayed an effective specific identification for NB and TNT. As a comparison, we summarized the fluorescence detection of various materials for TNT and NB molecules. To the best of our knowledge, the detection behavior of JUC-557-nanosheet for TNT (K a : 4.38 × 10 5 M -1 ) is more sensitive than previous fluorescence porous materials, such as other COFs (K a : ~ 8.5 × 10 3 M -1 ), MOFs (K a : ~ 1.83 × 10 2 to 2.02 × 10 5 M -1 ), and amorphous porous organic polymers (POPs, K a : ~ 7.04 × 10 2 to 2.56 × 10 4 M -1 , Fig. and Supplementary Table ). Meanwhile, the detection ability of JUC-557-nanosheet for NB (K a : 6.18 × 10 6 M -1 ) is higher than all optical detection materials reported as yet, such as MOFs (K a : ~ 220 to 4.47 × 10 6 M -1 ), POPs (K a : ~ 1.16 × 10 2 to 7.50 × 10 5 M -1 ), and even small molecule probes (K a : ~ 3.62 × 10 3 to 7.86 × 10 5 M -1 ) and inorganics (K a : ~ 9.00 × 10 2 to 1.45 × 10 5 M -1 , Fig. and Supplementary Table ). Also, the LOD of JUC-557-nanosheet was calculated to be 4.05 × 10 -11 M (5 ppb) and 5.71 × 10 - 10 M (129 ppb) for NB and TNT, respectively. Notably, the quenching rates did not decrease even after ten cycles of tests for both NB and TNT (Fig. and Supplementary Fig. ), and the fluorescence quenching was still obvious at titration concentration of only 5 × 10 -9 M for TNT and 5 × 10 -8 M for NB, respectively (Supplementary Figs. ), demonstrating the excellent stability and sensitivity of JUC-557-nanosheet for the detection of these nitro-compounds. As shown in Supplementary Figs. and, the TRPL spectroscopy exhibited that the lifetime of JUC-557-nanosheet did not change visibly (τ 0 /τ ≈ 1) with increasing amount of NB or TNT (from 0 to 40 µL), revealing a static quenching process, which could be originated from the formation of π-stacking complexes between nanosheets and NB or TNT molecules. The UV-vis absorption spectrum of JUC-557-nanosheet was obviously changed after the addition of TNT and NB, which further demonstrates the formation of π-stacking compounds (Supplementary Figs. and). Meanwhile, the fluorescence spectrum of NB or TNT obviously overlapped with that of JUC-557-nanosheet, which means the presence of energy transfer quenching mechanism between JUC-557-nanosheet with NB or TNT (Fig. ). In addition, due to the larger spectrum overlap of JUC-557-nanosheet with NB, the quenching effect of JUC-557-nanosheet for NB was better than that of JUC-557-nanosheet for TNT.