CHROMOPHORE CONCEPT & SOLVENT EFFECTS

1. CHROMOPHORE CONCEPT
AND
SOLVENT EFFECTS
1
Presented by;
SWEETY GEORGE
1st year M PHARM

2.  It is defined as the any isolated covalently
bonded group that shows a characteristic
absorption in the uv or visible region.
 Term chromophore was orginally used for
unsaturated groups of atoms which were
essential for colour.
CHROMOPHORE

3. Two Types
 INDEPENDENT CHROMOPHORE:
If only one chromophore is suffient to
impart colour in a compound then that chromophore is
refered as independent chromophore.
Eg: Azo group(N=N)
• DEPENDENT CHROMOPHORE
If more than one chromophore is required
to impart colour in the chromogen then that is refered as
dependent chromophore.
Eg:CH2=CH2 IS colourless.
;

4.  Chromophore in which the group contains ∏ electrons
and they under go n-> ∏* transition such
chromophore are ethylenes,acetylenes.
 chromophore which contain both ∏ electrons and n
electrons.such chromophores undergo two types of
transition.∏->∏*,n->∏*.
 Eg:carbonyls,nitrates.

5. Auxochrome
 The functional group with non-bonding electrons
that does not absorb radiation in near UV region but
when attached to a chromophore alters the
wavelength & intensity of absorption.
TWO TYPES
1. Basic or positive auxochromic groups(NH2,OH)
2. Acid or negative auxochromic groups(NO2,CO)

7. • When absorption maxima (λmax) of a
compound shifts to longer wavelength, it is
known as bathochromic shift or red shift.
• The effect is due to presence of an
auxochrome or by the change of solvent.
• Bathochromic Shift (Red Shift)1

8. • When absorption maxima (λmax) of a
compound shifts to shorter wavelength, it is
known as hypsochromic shift or blue shift.
• The effect is due to presence of an group
causes removal of conjugation or by the
change of solvent.
• Hypsochromic Shift (Blue Shift)2

9. • When absorption intensity (ε) of a
compound is increased, it is known as
hyperchromic shift.
• The shift is due to the change in structure of
a molecule and medium.
• Hyperchromic Effect3

10. • When absorption intensity (ε) of a
compound is decreased, it is known as
hypochromic shift.
• Hypochromic Effect4

11. Wavelength ( λ )
Absorbance(A)
Shifts and Effects
Hyperchromic shift
Hypochromic shift
Red
shift
Blue
shift
λmax

12. EFFECT OF SOLVENT
 The position and intensity of an absorption band may
shift when the spectrum is recorded in different
solvents.
 A dilute sample solution is preffered for analysis.
 Most commonly used solvent is 95% ethanol.It is best
solvent as it is cheap,transparent down to 210nm.

13. 1. n ->∏* transition.
Absorption band moves to shorter
wavelength by increasing the polarity of the
solvent.Ground state is more polar as compared to
the excited state.
Eg:absorption maximum of acetone is at 279nm in
hexane as compared to 264nm in water.
 ∏ ->∏* transition.
Absorption band moves to longer
wavelength by increasing the polarity of the solvent.

14. Choice of solvent
 It should not itself absorb radiations in the region
under investigations.
 It should be less polar so that it has minimum
interaction with the solute molecule.

15. Effect of solvent polarity on the
various types of bands
 K-band
Due to conjugated enes & enones are affected differently
by changing the polarity of the solvent.
K bands due to conjugated dienes are not affected by
changing the polarity of the solvent, while these bands
due to enones shows a red shift by increasing the
polarity of solvent.
 R band
The absorption shifts to shorter wavelength (blue shift)
with increasing polarity of solvent.

16.  B band
The position as well as the intensity of the band is not
shifted by increasing the polarity of the solvent. But
the heterocyclic aromatic compound, a marked
hyperchromic shift (increase in €max ) is observed by
increasing the polarity of the solvent.

17. EFFECT OF TEMPERATURE AND SOLVENT
ON THE FINENESS OF ABSORPTION BAND
 Vibrational & rotational states depends on
temperature.
“As temp decreased, vibrational & rotational state
of molecule is lowered.”
ie, when the absorption of light occurs at a lower
temp,smaller distribution of excited state results. It
produces finer structure in the absorption band than
what noticed at higher temp.

18.  Effect of solvent also affects the fineness of absorption
bands in the uv spectruum.
If the dielectic constantof the solvent is high,there
will be stronger solute-solvent interaction. Due to
this,vibrational and rotational energy states of a
molecule increase and thus fineness of absorption
band falls.