2,4,6-Trinitrophenol (TNP) has been widely used as a common explosive, but it pollutes the environment and the water source. The selective and sensitive detection of TNP in a water environment is of great importance. Herein, two facile and sensitive fluorescent sensing films (TCTSp-EP and OCTSp-EP) were constructed using tetrabazolyl- and octacarbazolyl-substituted spirobifluorene star-shaped molecules (TCTSp and OCTSp) by electrochemical polymerization. The TCTSp-EP and OCTSp-EP were found selective and sensitive towards the detection of TNP, with a limit of detection (LOD) value of 47.2 nM and 21.5 nM, respectively. The fluorescence detection of TNP was achieved through Förster resonance energy transfer (FRET) and photo-induced electron transfer (PET) as core TNP detection mechanisms. Compared with TCTSp-EP, the more carbazoles in the OCTSp-EP improved the electrical activity and increased the film thickness growth rate. The OCTSp-EP was more sensitive to TNP in water than TCTSp-EP. This was due to the hyperbranched structure of OCTSp-EP which had more exciton migration channels. Moreover, both of these films had excellent cycling performance and were successfully applied to detect TNP in real-water samples (deionized water, drinking water, and lake water).