Types of Chromophore

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Types of chromophore

Conjugated chromophore that straightens in response to a photon γ (light), of the correct wavelength: 11-cis-retinal becomes all-trans-retinal Chromophores almost always arise in one of two forms: conjugated pi systems (also known as resonating systems) and metal complexes. [edit]Conjugated pi-bond system chromophores

In the conjugated chromophores, the electrons jump between energy levels that are extended pi orbitals, created by a series of alternating single and double bonds, often in aromatic systems. Common examples include retinal (used in the eye to detect light), various food colorings, fabric dyes (azo compounds), pH indicators, lycopene, β-carotene, and anthocyanins. Various factors in a chromophore's structure go into determining at what wavelength region in a spectrum the chromophore will absorb. Lengthening or extending a conjugated system with more unsaturated (multiple) bonds in a molecule will tend to shift absorption to longer wavelengths. Woodward-Fieser rules can be used to approximate ultraviolet-visible maximum absorption wavelength in organic compounds with conjugated pi-bond systems. [edit]Metal complex chromophores

The metal complex chromophores arise from the splitting of d-orbitals by binding of a transition metal to ligands. Examples of such chromophores can be seen in chlorophyll (used by plants for photosynthesis), hemoglobin, hemocyanin, and colorful minerals such as malachite and amethyst {this paragraph needs correction: there are no d-orbitals in chlorophyll and the colour of amethyst is due to F-center}. A common motif in biochemistry is chromophores consisting of four pyrrole rings. These come in two types: * the pyrroles form an open chain, no metal: phytochrome, phycobilin, bilirubin * the pyrroles form a ring (porphyrin), with a metal in the center: heme, chlorophyll -------------------------------------------------

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