Since this paper is meant to cover some of the fundamentals of organic pigments, let the start be a thorough understanding of the title itself. First, it is necessary to appreciate that of the entire universe of the color experience we are going to try to understand just a few points about a very small subset of this experience: small, solid, usually crystalline particles which remain insoluble when put into plastic and which selectively absorb light of certain wavelengths (hence appearing to have color). Second, what do we mean by organic? Organic means containing as a basis the element carbon, but then some carbon compounds are excluded. Perhaps this isn't the best of definitions, but a full explanation could be quite lengthy. Inclusion of other elements is necessary to create colored compounds. For the organic colorants, the most likely other elements present are nitrogen, oxygen, and hydrogen, followed by a raft of others such as chlorine, fluorine, bromine, sulfur, calcium, sodium, barium, strontium, nickel, copper, and cobalt. Despite the presence of metals such as copper and nickel, compounds containing these can still be termed organic. What about the term chromophore? Well, something in the organic compound has to be responsible for creating the color by the selective absorbance of light. The chromophore is simply the part of the molecule that is responsible for that absorbance. Not all of the parts of the molecule participate equally in this function. The easy part of the title is diketopyrrolopyrrole: this is simply a particular chromophore which for the rest of the discussion will be abbreviated as DPP. The simplest molecule which has a DPP chromophore has the chemical formula C_(18)N_2O_2H_(12). This is not a very big chromophore; in comparison, some other molecules about this size are common sugars and calcium stearate, the latter of which might be used in your laboratory or plant as a dispersant or lubricant in the compounding of plastics. The last part is the word model; why is DPP a model chromophore? DPP is a good model for the organic chromophores because many of the properties of chromophores and the pigments which are derived from them are exhibited by the family of colorants generically called the DPP's.
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