Chromophore concept

CHROMOPHORE CONCEPT

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, NO 2

3. TYPES OF CHROMOPHORES 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 λ max C – C 1350 C = C 1900 C = O 1900 2800 O – H 1850 NO 2 2800 C 6 H5( 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, NH 2 , NHR, COOH, CN, Cl etc..

6. Two types : 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. 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 absorbance λ max

8. BATHOCHROMIC SHIFT/ RED SHIFT Shift of absorption maximum towards longer wavelength Due to presence of groups like OH, NH 2 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

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