The chromophores are the elements of the atom a molecule responsible for the color. In this regard, they are carriers of various electrons that, once stimulated by the energy of visible light, reflect the range of colors.
At the chemical level, the chromophore is responsible for establishing the electronic transition of the band of the absorption spectrum of a substance. In biochemistry, they are responsible for the absorption of light energy involved in photochemical reactions.
Colors The Background Colorful Color Wallpaper
The color perceived through the human eye corresponds to the unabsorbed wavelengths. In this way, color is a consequence of transmitted electromagnetic radiation.
In this context, the chromophore represents the part of the molecule responsible for the absorption of wavelengths in the visible range. What influences the reflected wavelength and thus the color of the element.
The absorption of UV radiation is carried out based on the wavelength received by the variation of the energy level of the electrons and the reception state: excited or basal. Indeed, the molecule acquires a certain color when it captures or transmits certain visible wavelengths.
Chromophore groups
Chromophores are organized into functional groups responsible for the absorption of visible light. Chromophores are normally made up of Carbon-Carbon double and triple bonds (-C = C-): such as carbonyl group, thiocarbonyl group, ethylene group (-C = C-), imino group (C = N), nitro group, nitroso group (-N = O), azo group (-N = N-), diazo group (N = N), azoxy group (N = NO), azomethine group, disulfide group (-S = S-), and the aromatic rings such as paraquinone and orthoquinone.
The most common chromophore groups are:
- Ethylenic chromophores: Ar- (CH = CH) n -Ar; (n≥4)
- Azo chromophores: -RN = NR
- Aromatic chromophores:
- Derivatives of Triphenylmethane:
- Derivatives of Anthraquinone
- Phthalocyanines
- Hetero-Aromatic Derivatives
Chromophore groups present electrons resonating at a certain frequency, which continuously capture or radiate light. Once attached to a benzene, naphthalene or anthracene ring, they enhance the uptake of radiation.
However, these substances require the incorporation of molecules of auxochromic groups, in order to reinforce the coloration, fixing and intensifying the role of chromophores.
Mechanism and function
At the atomic level, electromagnetic radiation is absorbed when an electronic transformation occurs between two orbitals of different energy levels.
When at rest, the electrons are in a certain orbital, when they absorb energy, the electrons go to a higher orbital and the molecule goes to an excited state.
In this process there is an energy differential between the orbitals, which represents the absorbed wavelengths. In effect, the energy absorbed during the process is released and the electron goes from excited to its original form at rest.
As a consequence, this energy is released in various ways, the most common being in the form of heat, or by releasing energy through the diffusion of electromagnetic radiation.
This luminescence phenomenon is common in phosphorescence and fluorescence, where a molecule lights up and acquires electromagnetic energy, going into an excited state; When reverting to a basal state, energy is released through the emission of photons, that is, radiating light.
Auxochromes
The function of chromophores is linked to auxochromes. An auxochrome constitutes a group of atoms that, coupled with a chromophore, modify the wavelength and intensity of absorption, influencing the way in which said chromophore absorbs light.
An auxochrom alone cannot produce color, but attached to a chromophore it has the ability to intensify its color. In nature, the most common auxochromes are hydroxyl groups (-OH), aldehyde group (-CHO), amino group (-NH2), methyl mercaptan group (-SCH3) and halogens (-F, -Cl, -Br, -I).
The functional group of auxochromes has one or more pairs of available electrons that, when attached to a chromophore, modify the absorption of the wavelength.
When the functional groups are directly conjugated with the Pi system of the chromophore, absorption is intensified as the wavelength that captures light increases.
How is the color changed?
A molecule has a color depending on the frequency of the absorbed or emitted wavelength. All elements have a characteristic frequency called the natural frequency.
When the wavelength is of a frequency similar to the natural frequency of an object, it is more easily absorbed. In this regard, this process is known as resonance.
This is a phenomenon through which a molecule captures radiation of a frequency similar to the frequency of the movement of electrons in its own molecule.
In this case, the chromophore intervenes, an element that captures the energy differential between different molecular orbitals that are within the light spectrum, in such a way, the molecule appears colored because it captures certain colors of visible light.
The intervention of the auxochromes causes the transformation of the natural frequency of the chromophore, so the color is modified, in many cases the color is intensified.
Each auxochromium produces certain effects on the chromophores, modifying the frequency of the absorption of wavelengths from different parts of the spectrum.
Application
Due to their ability to impart color to molecules, chromophores have various applications in the production of colorants for the food and textile industry.
Indeed, colorants have one or more chromophoric groups that determine the color. Likewise, it must have auxochromic groups that allow potential and fix the color on the elements to be colored.
The coloring product manufacturing industry develops particular products on the basis of specific specifications. An infinity of special industrial colorants have been created for any matter. Resistant to various treatments, including continuous exposure to sunlight and prolonged washing or harsh environmental conditions.
So, manufacturers and industrialists play with the combination of chromophores and auxochromes in order to design combinations that provide a colorant of greater intensity and resistance at low cost.
References
- Chromophore (2017) IUPAC Compendium of Chemical Terminology - the Gold Book. Recovered at: goldbook.iupac.org
- Santiago V. Luis Lafuente, María Isabel Burguete Azcárate, Belén Altava Benito (1997) Introduction to Organic Chemistry. Universitat Jaume IDL ed. IV. Title. V. Series 547. ISBN 84-8021-160-1
- Sanz Tejedor Ascensión (2015) The dye and pigment industry. Industrial Organic Chemistry. Valladolid School of Industrial Engineering. Recovered at: eii.uva.es
- Shapley Patricia (2012) Absorbing Light with Organic Molecules. Chemistry 104 Index. University of Illinois. Recovered at: chem.uiuc.edu
- Peñafiel Sandra (2011) Influence of softening with fatty acid bases in the change of hue in 100% cotton fabrics dyed with low reactivity reactive dyes. Digital Repository. North Technical University. (Thesis).
- Reusch William (2013) Visible and UltravioletSpectroscopy. IOCD International Organization for Chemical Sciences in Development. Recovered at: chemistry.msu.edu