Alkali resistance mechanism of cyano-containing heterocyclic disperse dyes

Dyes containing cyano group have the advantages of bright colours and high molar absorption. However, most cyano-containing disperse dyes are not used for alkaline dyeing as they are easily hydrolysed under alkali conditions. Herein, cyano-containing disperse dyes for alkaline dyeing were designed by introducing non-hydrolysable phenylethyl and potentially alkali-hydrolysable ethyl benzoate in adjacent positions to the cyano group, and the effect of the adjacent groups on the alkali resistance of cyano-containing dyes was investigated. Polyester fabric (PET) was dyed under different acidic or alkali conditions by the disperse dyes, then the hydrolysis energy barrier of cyano on the dye and the binding energy of dye-dye and dye-PET under the dyeing conditions were calculated via Density Functional Theory (DFT). The results showed that the cyano-containing disperse dyes with an adjacent benzene ring structure had good alkali resistance in a 5 g/L NaOH dye bath. DFT simulations confirmed that the adjacent phenylethyl did not have a significant effect on the hydrolytic energy barrier of the cyano group, while the adjacent ethyl benzoate reduced the hydrolytic energy barrier of the cyano group. The introduction of an adjacent benzene ring reduced the dye-dye binding energy, contributing to the increasement of dyeing rate at the beginning of the dyeing process. The designed cyano-containing dyes with adjacent benzene rings achieved a colour fastness level of 4–5 or above in various acid and alkali conditions.