Dyes are colored substances that are applied to materials to change their color. They work by absorbing certain wavelengths of light, which our eyes then perceive as color. Dyes are made up of chromophores, which are structures containing delocalized electrons that allow the dye to absorb specific wavelengths of visible light. Auxochromes are groups of atoms attached to chromophores that modify their light absorption properties and provide solubility. There are various ways to classify dyes, including by their chemical structure and the materials they can be applied to such as textiles, paper, leather, and more.

1. MADE BY:-
AAYUSHI SHAH
XII- SCIENCE
VEDANT INTERNATIONAL
SCHOOL

2. What is Dye?
Plastic toys for children to the fabrics you wear,
from food to wood; hardly there is any industry.
Coloring material that colors commodities of our
day to day use. Dyes are applied everywhere,
from a natural or synthetic substance used to
add a color or to change the color of something.
Dyes are the dyes are not used commercially.
A dye is a colored substance that has an affinity to
the substrate to which it is being applied. It is an
Ionizing and aromatic organic compounds. The
dye is generally applied in an aqueous solution,
and may require a mordant to improve the
fastness of the dye on the fiber.

3. With the help of dyes we can easily manipulate
things according to our liking. At the very
basic level the use of color in identifying
individual components of tissue sections can
be accomplished primarily with dyes. Dyes
are applied to numerous substrates for
example to textiles, leather, plastic, paper,
food etc.
The rule that we apply to other chemicals is
similarly applicable to dyes also. They also
get completely or at least partially soluble in
which it is being put to. For example certain
kind of dyes can be toxic, carcinogenic or
mutagenic and can be hazardous to health.

4. Dyes are basically ionising and aromatic
compounds. They have Chromophores
present in them. Their structures have Aryl
rings that have delocalized electron systems.
These structures are said to be responsible
for the absorption of electromagnetic
radiation that has varying wavelengths,
based upon the energy of the electron
clouds.
Chromophores make the dyes proficient in
their ability to absorb radiation.
Chromophores act by making energy
changes in the delocalised electron cloud of
the dye. This alteration invariably results in
the compound absorbing radiation within
the visible range of colors and not outside it.
Human eyes detect this absorption, and
responds to the colors.

5. Electrons may result in loss of color; their
removal may cause the rest of the electrons
to revert to the local orbits. A very good
example is the Schiff's reagent. As
Sulphurous acid reacts with Pararosanilin,
what happens is that a Sulphonic group
attaches itself to the compound's central
carbon atom. This hampers the conjugated
double bond system of the Quinoid ring, and
causes the electrons to become localised. As
a consequence the ring ceases to be a
Chromophore. As a result, the dye becomes
colorless.
To conclude, chromophores are the atomic
configurations which has delocalised
electrons. Generally they are represented as
carbon, nitrogen, oxygen and sulphur. They
can have alternate single and double bonds.

6. Auxochrome is the only substance responsible
for providing solubility and cohesiveness to
dyes. An auxochrome is a group of atoms
attached to a chromophore which modifies
the ability of that chromophore to absorb
light. Examples include the hydroxyl group (-
OH), the amino group (-NH2), and an
aldehyde group (-CHO).
The presence of an auxochrome in the
chromogen molecule is essential to make a
dye. However, if an auxochrome is present in
the Meta position to the chromophore, it
does not affect the color.
Auxochrome has the ability to intensify
colors. It is a group of atoms which attaches
to non-ionising compounds yet has the
ability to ionise. Auxochromes are of two
types, positively charged or negatively
charged.

7. Dyes can be classified in several ways; each
class has a very unique chemistry, structure
and particular way of bonding. Some dyes
can react chemically with the substrates
forming strong bonds in the process, and
others can be held by physical forces. Some
of the prominent ways of classification are
given below

Natural / Synthetic
 Organic / Inorganic
 By area and method of application
 Chemical classification - Based on the
nature of their respective chromophores.
 By nature of the Electronic Excitation
 According to the dyeing methods
 Anionic (for Protein fibre)
 Direct (Cellulose)
 Disperse (Polyamide fibres)

8. US International Trade Commission has advocated
the most popular classification of dyes. This
system classifies dyes into 12 types, which are
given below:
 Group
 Application
 Direct
 Cotton, cellulosic and blended fibres
 Vat dyes
 Cotton, cellulosic and blended fibres
 Sulphur
 Cotton, cellulosic fibre
 Organic pigments
 Cotton, cellulosic, blended fabric, paper
 Reactive
 Cellulosic fibre and fabric
 Disperse dyes
 Synthetic fibres
 Acid Dyes
 Wool, silk, paper, synthetic fibres, leather
 Azoic
 Printing Inks and Pigments
 Basic
 Silk, wool, cotton

9. The Dyes are classified based on the products
to which they can be applied and the chemical
nature of each dye. Dyes are complex
unsaturated aromatic having characteristics
like solubility, intense color, sub-stansiveness
and fastness. A dye-formulation is supposed
to have approximately 10-80% pure dyestuff.
It is mostly observed that dyestuffs delivered
in powder form have a higher value. While a
lower value is obtained for the liquid
formulations.