Synthesis, Spectroscopic Characteristics, DFT Study and Dyeing Performance of Bischlorotriazine Based Water-Soluble Reactive Dyes

Three reactive dyes, with bisbenzimidazole as the chromophore and bischlorotriazine as the active group, were synthesized and characterized. The photophysical properties of the dyes were discerned by UV-vis absorption, emission, and density functional theory calculations. All the dyes exhibited two absorption bands in the UV-vis region. The main band at 270 nm was attributed to the intramolecular π-π* transition, whereas the absorption at 360 nm was assigned to the π-π* mixed intramolecular charge transfer transitions. As the planarity of the benzimidazole components was enhanced, the energy gap of these dyes decreased, which caused a redshift. The relationship between the structure and dyeing properties of the dyes was also studied from the perspective of dyeing depth and fastness. The results showed that these dyes can be dyed on silk effectively, the dyeing depths were in the range of 0.08∼35 under salt-free conditions and the dry/wet rubbing fastness of these dyes could reach grades 4–5. In summary, these reactive dyes could be potential dyes for salt-free dyeing applications.