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 x 10(5) g mol(-1), 60 degrees 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. (c) 2013 Society of Chemical Industry