Another important application of cyanuric chloride is the synthesis of optical brighteners. These are compounds which absorb invisible UV-light and emit visible light primarily in the blue spectral range. The bluish fluorescence generated makes the yellow or yellowish substrates appear whiter.
Optical brighteners are therefore used in detergents, for the finishing of textiles, and in the manufacture of highly refined paper. The synthesis of optical brighteners proceeds via the reaction of 4,4'-diaminostilbene-2,2'-disulfonic acid with cyanuric chloride.