This document discusses chromophores and how they absorb electromagnetic radiation. It defines a chromophore as a covalently bonded group that absorbs UV or visible light. Common chromophores include C=C, C=O, and NO2 groups. Chromophores can be independent, requiring only one group to impart color, or dependent, requiring more than one group. Auxochromes are groups that alter the wavelength and intensity of absorption when attached to a chromophore. Absorption maxima can be bathochromically or hypsochromically shifted and absorption intensity can be hyperchromically or hypochromically altered.

1. CHROMOPHORE CONCEPT
PRESENTED BY;
AISWARYA.A.T
I MPharm.,
DEPARTMENT OF PHARMACY PRACTICE
GRACE COLLEGE OF PHARMACY

2. CHROMOPHORE
 Defined as any isolated covalently bonded group
that shows a characteristic absorption of
Electromagnetic radiation in the UV or visible
region.
It is a Greek word.
Chroma = “color” & phoros = “bearer”
Compound containing chromophore is CHROMOGEN
Eg: C=C, C=O, NO2

3. TYPES OF CHROMOPHORES
1. INDEPENDENT CHROMOPHORES
If one chromophore is required to impart colour
Eg: Azo group –N=N-, Nitroso group –NO-
2. DEPENDENT CHROMOPHORES
If more than one chromophore is required to impart colour
Eg: Acetone having one ketone group is colorless whereas
diacetyl having two ketone groups is yellow.

4. Groups λmax
C – C 1350
C = C 1900
C = O 1900
2800
O – H 1850
NO2 2800
C6H5( PHENYL) 1950
2500
SIMPLE CHROMOPHORIC GROUPS

5. Auxochrome
A saturated/ unsaturated group with non bonding
electrons when attached to chromophore altering both
wavelength as well as intensity of absorption.
Eg: OH, NH2, NHR, COOH, CN, Cl etc..

6. Two types:
1) Basic/positive auxochromic groups
Effective in acid solutions
Eg: OH, OR, NHR etc.
2) Acidic/negative auxochromic groups
Effective in alkaline solutions
Eg: NO, CO, CN etc.

7. CHANGESIN POSITION& INTENSITYOF ABSORPTION
For isolated chromophore groups such as –C=C- absorption
takes place at far UV which cannot be easily studied but the
position & intensity can be modified:
bathochromic
hypsochromic hyperchromic
hypochromic
200 wavelength 800
absorbance
λ max

8. BATHOCHROMIC SHIFT/ RED SHIFT
•Shift of absorption maximum towards longer
wavelength
•Due to presence of groups like OH, NH2 etc.
(auxochromes)
Eg: ethylene shows absorption at 170nm whereas
1,3-butadiene shows at 217nm.

9. HYPSOCHROMIC SHIFT / BLUE SHIFT
•Shift of absorption maximum towards shorter
wavelength
•May be caused by removal of conjugation
Eg: In Aniline, absorption takes place at 280nm.
In acidic solutions, absorption takes place at
200nm

10. HYPERCHROMIC SHIFT
Increase in intensity of absorption
By introduction of ‘auxochrome’
Eg: introduction of methyl group in position 2 of
pyridine increases intensity of absorpion from
2750 to 3560
HYPOCHROMIC SHIFT
Decrease in intensity of absorption
Eg: introduction of methyl group in position 2 of
biphenyl group causes hypochromic effect because
of distortion

11. THANK YOU!!!