1.
Dyestuff and Color Science
TET-304
Engr. Nasir Sarwar

2.
Dye stuff
• Dye:
• An ionized aromatic compound that have the
ability impart color to the substrate on which
these are applied, is termed as DYE.
• All dyes contains aromatic compounds.
• Substrate may be textile(Fiber, fabric, paper,
leather, plastics wax, cosmetic base etc.

3.
• Aromatic compounds are substances that
consist of one or more rings that contain
alternating single and double bonds in its
chemical structure.
• Benzene

4.
Other Examples

5.
• A dye is a colored substance but every colored
substance are not dye.
• e.g. Azo benzene – Red in color but not Dye
Why…

6.
Properties of Dye
• Stable Structure- Should not go structural
change easily.
• Should have affinity for its substrate.
• Should be soluble in water or in any suitable
media or made stable dispersion.
• After application should resist to certain
physical/chemical action with acceptable
limits.

7.
What is color
The perception of colour is an ability of some
animals, including humans, to detect some
wavelengths of electromagnetic radiation (light)
differently from other wavelengths.
When light fall on any object it absorbs to some
extant and shows reflectance, transition and
scattered.
The potions of light in visible spectrum of light
reaches to our eye is detected as color

8.
• Color is nothing just the rays of certain wave
length that detected by our eye.
• electrons fall to lower energy levels and give
off light in the form of a spectrum.
• These spectral lines are actually specific
amounts of energy for when an electron
transitions to a lower energy level.
• Electrons can only occupy specific energy
levels in an atom to be stabilized.

9.
• Electron jumps and release energy in form of
rays of different wave length.

10.
• When an object absorbs some of the radiation
from within that range we see the waves that
are left over, and the object appears coloured.
In reality this range we see makes up only a
very small fraction of the electromagnetic
spectrum.
• Human Eye respond to wavelengths between
about 400-700 nm.

11.
What makes Dye Colored
Is It chromophore???

12.
• The absorption of electromagnetic radiation
of varying wavelengths, depending on the
energy of the electron clouds. For this reason,
chromophores do not make dyes coloured in
the sense that they confer on them the ability
to absorb radiation.

13.
• chromophores function by altering the energy
in the delocalised electron cloud of the dye,
and this alteration results in the compound
absorbing radiation from within the visible
range instead of outside it. Our eyes detect
that absorption, and respond to the lack of a
complete range of wavelengths by seeing
colour.

14.
Examples of Chromophor

15.
Auxochrome

16.
Auxochrome
• The word auxochrome is derived from two
roots. The prefix auxo is from auxein, and
means increased. The second
part, chrome means colour, so the basic
meaning of the word auxochrome is colour
increaser. This word was coined because it
was noted originally that the addition of
ionising groups resulted in a deepening and
intensifying of the colour of compounds.

17.
Effect of auxochrome aromatic system
To the left is naphthalene, a colourless compound.
The addition of a single hydroxyl group to naphthalene
produces 1-naphthol which is also a colourless
compound, but one which can ionise.
If instead of a hydroxyl group we add the nitro
group, which is a chromophore, we get the
compound 2,4-dinitronaphthalene. The addition of
this chromophore has caused it to become pale
yellow.
If instead of a hydroxyl or nitro groups, both a
hydroxyl and nitro groups are added, we get the deep
yellow dye, martius yellow.

18.
Modifiers
• Groups that alter the colour of dyes by altering
the energy in the delocalized electrons.
• They themselves cannot do this enough to cause
absorption in the visible range, but they can
affect the shade significantly when absorption is
already in that range. Adding more of a particular
modifier results in a progressive alteration of
colour.
• Example - the Methyl violet series*.

19.
Modifier
Without any methyl groups the parent dye is
called pararosanilin and is red.
When four methyl groups are added we get
the reddish purple dye methyl violet.
As more methyl groups are added we get the
purple blue dye crystal violet which has six
such groups.
If a seventh methyl group is added, the
resulting dye ismethyl green.

20.
Terms associated with Dyes
Hue: The degree of stimuli of absorbing specific
wavelength.
For understanding, any of basic these basic color
is Hue
These are the family of twelve purest colors.
• Three Primary Colors (RGB)
• Three Secondary Colors(?)
• Six Tertiary Colors(?)

21.
Strength: Absorbance of Dye at a particular
Wavelength.
A dye with batter strength have deeper shade%
at low concentration.
Bathochromic Shift
A structural change which causes the absorption band to
longer wavelengths (i.e. yellow -> orange -> red, violet ->
blue -> green) is called a bathochromic shift.

22.
The reverse shift, towards shorter wavelengths is
known as a hypsochromic effect.
• Chromophors- Electron withdrawing groups
• Auxochrome- Electron donating groups
A bathochromic shift may be caused by increasing
the electron-withdrawing power of the
chromophore (X or Y), increasing the electron-
donating power of the auxochrome (Y or X) and by
increasing the length of the conjugated system
connecting the two.

23.
The position of the chromophore and
auxochrome also has an effect. In general, the
meta position (M) has the shortest wavelength,
and the para (P) and ortho (O) absorption
wavelengths are approximately equal, and
longer than meta.

24.
Groups-cause more bathochromic shift

25.
Photochromism
Photochromism is the reversible transformation
of a chemical species between two forms by the
absorption of electromagnetic radiation, where
the two forms have different absorption spectra.
It is consider a fault in textile.
It is due to different isomeric position of stable
dye structure.

26.
Cis/Trans Isomerisim
The terms “cis” and “trans” are from Latin, in
which cis means "on this side"[ and trans means
"on the other side" or "across".
As with any double bond, the planar -N=N- bond
shows geometrical isomerism
Trans Cis

27.
• Trans form is more stable than cis.
• Strong polar group, less will be
photochromism