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How can absorbed light affect the color of a molecule?

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representations of molecular structure — molecule Several methods of representing a molecule's structure. In Lewis structures, element symbols represent atoms, and dots represent electrons surrounding them. A pair of shared electrons (covalent bond) may also be shown as a single dash. The ball-and-stick model better illustrates the spatial arrangement of the atoms. For aromatic compounds, the Kekulé structure is common, in which each bond is represented by a dash, carbon atoms are implied where two or more lines meet, and hydrogen atoms are usually omitted. Bond-line formulas, similar to the Kekulé structure, are often used for complex nonaromatic organic compounds. Sugars are often drawn as Fischer projections, in which the carbon “backbone” is drawn as a straight vertical line, with carbon atoms implied where horizontal lines intersect the vertical one.

The color of a molecule is determined by its interaction with light in the visible spectrum. When a molecule absorbs specific wavelengths of light, it promotes electrons from a low-energy molecular orbital to a higher-energy, unoccupied orbital.1

The observed color of the compound is the result of the light that is not absorbed—specifically, the light that is transmitted or reflected. Because human perception of color is the inverse of the absorption spectrum, a molecule appears colored based on the wavelengths it fails to absorb.21

Several structural factors influence this process:
* Chromophores: These are specific groups of atoms and electrons within a molecule capable of absorbing visible light.23
* Conjugation: Molecules with extensive systems of conjugated pi bonds can absorb light at longer wavelengths and lower energies. As the number of conjugated bonds increases, the absorption shifts, often resulting in intense colors, such as the orange of beta-carotene.4
* Coordination Compounds: In transition metal complexes, electronic transitions between d-level orbitals can also lead to distinct visible absorption and coloration.3