Synthesis, characterization and fluorescence performance of a waterborne polyurethane‐based fluorescent dye 4‐amino‐ N ‐cyclohexyl‐1,8‐naphthalimide, WPU‐ACN

A waterborne‐polyurethane‐based fluorescent dye 4‐amino‐ N ‐cyclohexyl‐1,8‐naphthalimide ( WPU‐ACN ) was synthesized by attaching 4‐amino‐ N ‐cyclohexyl‐1,8‐naphthalimide ( ACN ) into polyurethane chains according to a prepolymer−ionomer process. The structure of WPU‐ACN was confirmed by means of Fourier transform infrared spectroscopy and UV −visible absorption. The number‐average molecular weight, glass transition temperature and average emulsion particle size for WPU‐ACN were determined as 7.8 × 10 5 g mol −1 , 60 °C and 60 nm, respectively. The improved thermal stability of WPU‐ACN could be attributed to the incorporation of naphthalimide units in the preformed urethane groups. The fluorescence intensity of WPU‐ACN was dramatically enhanced compared with that of ACN . It was found that the fluorescence intensity of WPU‐ACN increased with increasing temperature, and the fluorescence spectra of WPU‐ACN showed a positive solvatochromic effect. In addition, the fluorescence of WPU‐ACN emulsion was very stable not only for long‐term storage but also for fluorescence quenching.