Clusterization-Triggered Emission of Waterborne Polyurethane: The Role of Carboxyl Groups

The intrinsic luminescent properties of waterborne polyurethane (WPU) as an industrial-scale nonconjugated polymer and the role of side groups in its intrinsic luminescence remain unclear and require further exploration. In this work, a series of WPUs with different side carboxyl contents were prepared, which exhibit clusterization-triggered emission (CTE) characteristics. The carboxyl group of the side carboxyl groups strengthened the hydrogen bond, electron overlap between lone pairs and π electrons, and dipole–dipole and n–π* interactions, thereby enhancing the emission intensity. Furthermore, leveraging the clusteroluminescence characteristics of WPU, various applications have been developed, including explosive and Fe³⁺ detection, damage tracing, and stretch fluorescence change. This work not only enhances our understanding of the clusteroluminescence mechanism but also provides an effective approach for designing and operating nonconjugated fluorescent materials.