Hyperbranched Fluorescent Polymers for the Detection of 4-Nitrophenol and Their Antibacterial Performance

p-Nitrophenol (4-NP), a typical nitroaromatic pollutant, is of great importance for rapid and selective detection. In this study, hyperbranched polymer probes (FL-HBP-1, FL-HBP-2, and FL-HBP-3) with 4-NP recognition, adsorption, and antibacterial abilities were prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization. Initially, a RAFT chain transfer agent (CTA-NO2) containing nitro groups and carbon–carbon double (C═C) bonds was synthesized using N-methyl-4-nitrobenzenamine and 4-vinylbenzyl chloride as starting materials. Subsequently, the nitro group was reduced to an amino group. Meanwhile, a fluorescent unit (NN) containing a naphthalimide fluorescent group and a polymerizable double bond (C═C) was introduced into the polymerization system. Through RAFT polymerization, a hyperbranched fluorescent polymer (FL-HBP-1) with fluorescence response capability was successfully obtained. On this basis, functional monomers bearing quaternary ammonium groups, namely diallyldimethylammonium chloride (DADMAC) and allyltrimethylammonium chloride (ATMAC), were further introduced to synthesize FL-HBP-2 and FL-HBP-3 with antibacterial performance. All three polymers exhibited narrow polydispersity indices (PDI) of 1.056, 1.061, and 1.155, respectively. FL-HBP-1, FL-HBP-2, and FL-HBP-3 exhibited selective 4-NP recognition with low detection limits of 6.72 nM, 2.52 nM, and 4.03 nM, respectively. Moreover, the polymers demonstrated 4-NP adsorption capability with a removal efficiency of 44.7%. Furthermore, the introduction of quaternary ammonium monomers endowed FL-HBP-2 and FL-HBP-3 with strong antibacterial activity. These multifunctional polymers show great potential for pollutant treatment and microbial inhibition.