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

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.