Chemistry of Colors: Where Does Our Spectrum Come From?

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Illustration of white (visible) light spectrum

Illustration of white (visible) light spectrum, Image courtesy of NASA

Everyone seems to have a favorite color. But, to most scientists, having a favorite color relates to its constituents. Colors are a matter of mathematics and geometry; the intimate language of nature.

When Isaac Newton discovered sunlight constituted a rainbow of colors, he helped us to understand the underpinnings of color.

Our visual perception of blue or red is actually only one part of the many individual units of white light.

Furthermore, each unit of color corresponds to a ‘different unit number (or wavelength)’ within the rainbow (or spectrum of colors).

From red to violet, you can examine the corresponding numbers and you may reach the conclusion life is ordered in a numerically consistent manner.

Colors, Wavelengths, and Our Visual Perception

Wavelengths of colors

What wavelength do colors match? Image by John Jaksich, all rights reserved

When examining the colors of different substances, certain hues and shades will correspond to differing numerical units or wavelengths.

One particularly easy example is color red-orange (625 nm) which could correspond to a carrot or shade of tomato.

The principle molecular constituent is beta-carotene, its molecular structure (scaffolding) is a complex system of atoms that is noted to be a linear:

beta_carotene

Chemical structure of beta-carotene, Image courtesy of NIH

Shortening the molecule by eliminating portions of the chain corresponds to another important, colorful molecule gives Vitamin A (corresponds to yellow or 550 nm).

vitamin a

Chemical structure of Vitamin A, Image courtesy of NIH.

Another important, colorful molecule is hemoglobin (blood). Everyone is familiar with its scarlet coloration; its responsible unit is heme, also known as haem:

This is the chemical structure of heme, also known as haem, which furnishes the color of hemoglobin. Image courtesy of NIH http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=53629486

The color-furnishing portion of hemoglobin, Courtesy of NIH

While molecules similar to heme (such as chlorophyll) may induce a different color sensation, the principles behind the sensation of color are under the laws of quantum mechanics. From substances that look red to others that appear green, there must be a light reaction – the same light constituting a rainbow (or spectrum of colors).

Sunlight, Chlorophyll, and Wavelengths

In sun light, chlorophyll will absorb purple light and emit green light. It does this because all matter will absorb light and will emit it at a different wavelengths. In fact, once a molecule absorbs at a certain wavelength it will emit at lower wavelength—it must do so. The ‘energy’ associated with absorbance is re-distributed throughout the molecule. The light energy can go only two places—absorbing the light and emitting it.

Chlorophyll Molecule, Image Courtesy of NIH, http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=57390544&loc=es_rss

Chemical structure of a Chlorophyll Molecule, Image Courtesy of NIH

When envisioning the absorbance and emission of light, you can come away with the following:

Each substance or material contains molecules that can characterize it unambiguously. The geometry (or scaffolding) of the molecule is unique. The uniqueness conveys a manner by which we may use light to identify it. Vitamin A and beta-carotene are similar substances but they may be identified, in part, by their coloration.

We usually use other forms of light (infrared, ultraviolet or x-ray)  in conjunction with the visible (rainbow spectrum) to identify molecular constituents of a material. When presented with a material that we cannot unambiguously identify with one form of light, the other forms of light help piece the puzzle together.

Chemistry, Light, And Structure of Color

Perhaps by understanding that we can identify each material and its unique structure with different forms of light, we may seek to understand nature, as well.

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