Synthesis of novel bisazo disperse dyes: Spectroscopic characterization, DFT study and dyeing of polyester

A series of bis azo disperse dyes were synthesized starting from benzidine and four couplers contain active methylene group, namely; thiobarbituric acid, barbituric acid, dimedone and thiohydantoin, to give 3 a-c and 4, respectively. The dye products were identified by UV-visible, FT-IR, H-1 NMR and C-13 NMR spectroscopy. The electronic absorptions of the synthesized dyes indicated that the lambda(max) are slightly dependent on the coupler moieties and quite sensitive to pH change. Dyeing of polyester yarn(PE-Y) was done in DMF, whereas, polyester fabric (PE-F) was dyed in water using dispersing agent DYEWELL-002. Fastness properties of bis azo dyes 3a-c and 4 on PE-F are better than those of PE-Y. The summation of color strength (K/Ssum) values of PE-F followed the order 3c > 4 > 3a > 3b. The DFT method was used to calculate the chemical descriptor parameters of the protonated form of bis azo dyes 3a-c and 4, using B3LYP/6-31G(d,p) level for investigation of dyeing efficiencies as well as to predict the mechanism of dyeing process. The computed results point out that dye 3a has the highest dyeing strength based on E-HOMO, E-LUMO, Delta E, eta and S parameters while dye 4 is the highest depending on chi and mu eV parameters. The correlation results of the computed parameter with color strength (K/S) and Exhaustion (%E) in case of PE-Y indicated that they depend mainly on the effect of electronegativity chi with correlation coefficient 0.993 and 0.877, respectively. In a similar way, the PE-F exhibits very good effect of color strength with dipole moment (R-2 = 0.899). The protonated dyes 3a-c and 4 can adsorbed on the PE surface either by hydrogen bond or/and electrostatic attraction.