What is a chromophore? and an auxochromo?
Answer:
Chromophores are extended delocalised systems of electrons in a compound which gives it its colour, e.g. chlorophyll's porphin ring, or an azo dye's benzene rings joined by a N=N double bond.
Auxochromes are functional groups attached to chromophores that alter the shade of colour it emits, e.g. -OH and -NH2 groups.
Chromophore
A chromophore is part (or moiety) of a molecule responsible for its color.
When a molecule absorbs certain wavelengths of visible light and transmits or reflects others, the molecule has a color. A chromophore is a region in a molecule where the energy difference between two different molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state.
In biological molecules that serve to capture or detect light energy, the chromophore is the moiety that causes a conformational change of the molecule when hit by light.
Chromophores almost always arise in one of two forms: conjugated pi systems and metal complexes.
In the former, the energy levels that the electrons jump between 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), lycopene, β-carotene, and anthocyanins.
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.
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: hemoglobin, chlorophyll
Auxochrome (correct spelling)
Auxochrome - this is a group of atoms attached to a chromophore which modifies the ability of that chromophore to absorb light. Example: -OH , - NH2 , Aldehydes Attached group which enables the attached of the coloured molecule Add a chemical group to the molecule of the dye so as to enable its attachment to the tissue structures while without changing its colour or stability. If these groups are in direct conjugation with the pi-system of chromophore, they may increase the wavelength at which the light is absorbed and as a result intensify the absorption. A feature of these auxochromes is the presence of at least one lone pair of electrons which can be viewed as extending the cojugated system by resonance.
In a pigment the chromophore is that part of the structure which imparts the basic hue, frequently this is an R-N=N-R1
type struture, where R nd R1 are aromatic ring structures as in the Diarylide Yellows (CI Pigment Yellows 13 and 83 are the best examples)
The Auxochromes modify the hue by pulling or pushing on the electrons in the rest of the molecule.
CI Pigment Blue 15.4 is a bright clean cyan shade of blue often used in 4 colour printing. (The structure is to complex to draw here). . However if the molecule is cholorinated, the chlorine acts as an auxochrome changing the shade to a bright green. This is CI Pigment Green 7
chromophore - the chemical group that gives color to a molecule
Auxochrome - this is a group of atoms attached to a chromophore which modifies the ability of that chromophore to absorb light. Example: -OH , - NH2 , Aldehydes
The answers post by the user, for information only, FunQA.com does not guarantee the right.
More Questions and Answers: