A Blue Tunable Waterborne Polyurethane‐Based Carbon Nitride With Wide Excitation‐Wavelength‐Dependent Fluorescence

ABSTRACT Excitation wavelength‐dependent fluorescent materials are a class of materials whose fluorescence emission spectra drift significantly with excitation wavelength. Herein, carbon nitrides (CNNPs) emitting blue fluorescence were synthesized by a one‐pot method using urea as a conjugated monomer and L‐phenylalanine as a co‐precursor. Waterborne polyurethane‐based carbon nitride (CNNPs‐WPU) with excitation wavelength‐dependent fluorescence properties was produced by accessing amino(‐NH 2 )‐rich CNNPs to waterborne polyurethane (WPU) using a modified acetone method. The results show that CNNPs‐WPU has good storage and thermal stability. The fluorescence quantum yield (15.8%➔17.6%) and fluorescence lifetime (5.441 ns➔8.305 ns) of CNNPs‐WPU were higher than those of CNNPs. It is worth mentioning that between 310 and 390 nm, with the rising excitation wavelength, the emission wavelength of CNNPs‐WPU redshifts from 411 to 443 nm, CNNPs‐WPU exhibits obvious excitation wavelength‐dependent fluorescence characteristics, and the emission intensity increases with the increase of excitation wavelength, which makes it potentially applicable in the fields of anticounterfeiting, bioimaging, and light‐emitting devices, etc. Moreover, the CNNPs‐WPU uses water as the dispersed phase, which is green and environmentally friendly; it has a broad application prospect.