CHROMOPHORE CONCEPT

PRESENTED BY;

AISWARYA.A.T

I MPharm.,

DEPARTMENT OF PHARMACY PRACTICE

GRACE COLLEGE OF PHARMACY

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

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.

Groups λmax

C – C 1350

C = C 1900

C = O 1900 2800

O – H 1850

NO2 2800

C6H5( PHENYL) 19502500

SIMPLE CHROMOPHORIC GROUPS

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..

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.

CHANGES IN POSITION & INTENSITY OF 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

ab

sorb

ance

λ max

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.

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

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

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