Density functional theory in dye chemistry: between the light and the dark side

Some of the most common errors in using density functional theory (DFT) for structural analysis and prediction of the properties of organic azo dyes are considered. The importance on the stabilizing strength of the intramolecular hydrogen bonding, the crucial role of performing conformational analysis and selecting suitable level of theory are discussed using previously published theoretical paper on 2-2′-(5-nitrothiazolyl)azo-4-methoxyphenol as a study case. The use of the DFT properties prediction is considered in the frame of the experimental conditions at which they could be measured. It is shown in educational manner why most of the azo dyes do not emit. Although an azo compound is used as example, in general, the same errors and overinterpretations are encountered often when the DFT is applied in the organic chemistry.