Organic pigments are primarily composed of organic compounds, meaning they are carbon-based. These compounds provide the color and are typically synthetic, although some natural organic pigments exist.
Here's a breakdown of their composition:
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Core Chromophore: This is the heart of the pigment molecule and is responsible for its color. The chromophore is a specific arrangement of atoms (often including conjugated double bonds) that absorbs certain wavelengths of light and reflects others, which we perceive as color. Different chromophores produce different colors. Examples include:
- Azo pigments: Characterized by the presence of one or more azo groups (-N=N-) linked to aromatic rings. These are among the most widely used organic pigments due to their versatility and relatively low cost.
- Phthalo Blue and Green: Based on a phthalocyanine structure, these pigments are known for their exceptional color strength, lightfastness, and chemical resistance.
- Dioxazine Violet: This pigment utilizes a dioxazine chromophore, resulting in a vibrant violet hue with good lightfastness.
- Quinacridone pigments: These pigments offer a range of colors, from red and magenta to violet and orange, and are highly valued for their excellent lightfastness and weather resistance.
- Polycyclic Aromatic Carbonyl Pigments: This family includes pigments like perylenes, anthraquinones, and thioindigos, generally known for their high performance properties, such as light fastness, and solvent resistance.
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Substituents: Chemical groups attached to the chromophore modify the pigment's properties, such as hue, intensity, lightfastness, solubility, and dispersion characteristics. These substituents can fine-tune the color and improve the pigment's performance in specific applications.
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Additives (Sometimes): While not part of the core pigment molecule, additives may be incorporated during the manufacturing process to improve dispersion, stability, or other properties. These are generally present in small quantities.
In summary, organic pigments are complex molecules built around a chromophore, whose color and properties are influenced by its chemical structure and any attached substituents. The specific composition varies greatly depending on the desired color and application. Although some natural sources exist, most organic pigments used today are synthetic, allowing for greater control over their properties and availability.
