Effect of conformation on UV-Vis absorption spectra of disazo reactive red dyes

In this study, twenty disazo reactive red dyes with J acid as coupling components were selected, and their ground state geometry were studied with BLYP functional and TZVP basis set. The UV-vis absorption spectra were calculated by time-dependent density functional theory (TDDFT) employing B3LYP and PBE0 hybrid functionals and TZVP basis set, and the absolute mean errors are 0.094 eV and 0.133 eV for B3LYP and PBE0, respectively. From the comparison of the calculated λ _max of the three conformations of disazo reactive red dye, cis-, trans-, and azo, with that of experimental one, we find out that conformation plays an important role on UV-Vis absorption. Dyes 6 and 8 exist in azo conformation rather than in cis-conformation. “Hole-electron” distribution analysis reveals that although these λ _max arises from different electron transitions, these electron excitations have the same character of local excitation (LE).