Chromophore

 

UV-Visible spectroscopy

Chromophore

}  Chromophore is that part of a molecule which enable it to be colored.

}  Chromophore is any isolated covalently bonded group that shows a characteristic absorption in the ultraviolet or visible region (200-800 nm).

}  chromophores are of two types

Types

v  A: Chromophores which contain P electron and undergoes pi* to pi* transition.

}  This type of transition occurs in molecules like Ethylenes and acetylenes.

v  B: Chromophores which contain p electron as well as nonbonding electron.

}  These molecules undergoes two kind of transition

}  Transition from pi* to pi* and as well nonbonding to pi* transition. Examples are Carbonyl, nitriles, azo compounds, nitro compounds.

}  Auxochrome

}  It can be defined as a functional group present in an atom which doesn’t act as chromophore but its presence brings out a change in the absorption band of wavelength of a spectrum.

}  An auxochrome is a functional group of an atoms having one or more lone pairs of electrons when attached to a chromophore, brings about change both in the wavelength and intensity of absorption.

}  Auxochrome includes –OH,-OR,-NH2,-NHR,

    -SH etc

Bathochromic shift

}  Bathochromic shift or red Shift

}   Bathochromic shift is an effect where due to presence of an auxochrome or solvent change the absorption maximum is shifted towards the longer wavelength.

}   The nonbonding to pie* transition of carbonyl compounds observes bathochromic or red shift.

Hypsochromic shift

}  Hypsochromic shift or blue shift

}  Hypsochromic shift is an effect by virtue of which absorption maximum is shifted towards the shorter wavelength.

}  This happens due to the removal of conjugation or by changing the polarity of the solvents.

Hyperchromic effect

}  Hyperchromic effect

}  Hyperchromic effect is an effect due to which increase in the intensity of absorption maximum occur.

}  Hyeprchromic effect in a molecule increase its ability to absorb light.

}  Auxochrome introduction in compound generally results in the hyperchromic effect.

Hypochromic effect

}  Hypochromic effect

}   Due to the presence of hypochromic effect intensity of absorption maximum decreases.

}  Hyepochromic effect in a molecule decrease its ability to absorb light.

}  Hypochromic effect occurs due to the distortion of the geometry of the molecule with an introduction of new group.