Hypsochromic shift

As a hypsochromic effect, also blue shift is defined as the shift of the absorption spectrum of a substance in the shorter wavelength, higher energy region of the electromagnetic spectrum.

Happens when changing from a nonpolar to a polar solvent, one also speaks of solvatochromism. The hypsochromic effect resulting in this case from the stabilizing effect of the hydrogen bonding of the polar solvent on the organization responsible for the absorption in the relevant wavelength range -free and non -bonding electron pairs (n- orbitals ) and the antibonding π * orbitals (see molecular orbital theory). The n- orbitals have a bigger stable than the π * orbitals, which results in a larger energy difference to the result, and this in turn calls according to law

Shows absorption at shorter wavelengths. Cause a hypsochromic effect can also be a substitution or elimination reaction in a molecule, wherein a chemical group of the molecule is replaced by another, or completely removed. These substituents, its replacement or elimination causes such effects are called Auxochromes.

Reason for the shift of the absorption band towards shorter wave lengths in such substitutions, or eliminations, is the reduction of the delocalized π - electron system - it extends over the more conjugated double bonds, the greater are the wavelengths of light that is able to absorb it, and vice versa. The fewer conjugated double bonds has a π -electron system, the shorter the wavelength of the light that is capable of absorbing it. Reactions that are required to address such effects, therefore, play a major role in the synthesis of dyes.

Related terms

The opposite of the hypsochromic effect, so the shift of the absorption spectrum of a substance in the direction of longer wavelengths, is known as the bathochromic effect.

• Photochemistry
• Spectroscopy