Prediction of the color of dyes by using time-dependent density functional theory (TD-DFT)

Time-dependent density functional theory calculations (6-31+G* basis set) at four functional levels of theory (B3LYP, B97XD, M06-2X, and PBE0) have been performed in order to estimate their applicability to predict the visible spectra of organic colorants. The absorption wavelength calculations give the following order of performance: M06-2X>B97XD>PBE0>B3LYP when set of ionic and neutral dyes is used. In the case of neutral dyes only, the performance at all time-dependent PBE0, B97XD and M06-2X methods is statistically comparable. The importance of the specific interactions on the max prediction in the case of anionic phenylhydrazone dyes is shown. The comparison between experimental and calculated oscillator strengths was possible only in the case of anthraquinone dyes and has shown that all four methods predict reasonably well the trend of change of the oscillator strength as function of the substituents.