Theoretical design, prediction and synthesis of a magenta dye SCFX-AYRL for sustainable coloration of natural fibers in SCF-CO2

A special magenta dye SCFX-AYRL with dichlorotriazine as reactive group, designed as one of supercritical trichromatic dyes, was successfully synthesized for sustainable coloration of natural fibers in supercritical fluid of carbon dioxide (SCF-CO 2 ). The products were characterized and tested by FT-IR, 1 H NMR, LC-MS, EA and Uv-Vis spectra. Moreover, Gaussian software was also employed to assist a theoretical design of the dye and its precursor, such as the optimization of structure conformations, the calculation of frontier molecular orbitals and parameters, and the prediction of characteristic absorption wavelength. The obtained results show that the molecular structure and color characteristics of the synthesized dye well met the expected theoretical design and calculations. Particularly, the powerfully excited molecular orbitals facilitated the first electron transition from the highest occupied orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) by contributing characteristic singlet absorption bands for the precursor and its target dye. Moreover, an energy gap (Δ E ) calculation between the LUMO and the HOMO was performed to predict color hue shift, and was well consistent with experimental detects. A successful application of the special dye on natural protein fibers was observed for eco-friendly coloration in SCF-CO 2 with high color strength, fixation efficiency over 90.0 %, as well as high brilliant color and fastness.