Hypsochromic shift

Hypsochromic shift (from ancient greek ὕψος (upsos) "height") is a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a shorter wavelength (higher frequency). Because the blue color in the visible spectrum has a shorter wavelength than most other colors, this effect is also commonly called a blue shift.

This can occur because of a change in environmental conditions: for example, a change in solvent polarity will result in solvatochromism. A series of structurally related molecules in a substitution series can also show a hypsochromic shift. Hypsochromic shift is a phenomenon seen in molecular spectra, not atomic spectra - it is thus more common to speak of the movement of the peaks in the spectrum rather than lines.

$\Delta\lambda = \lambda^{\mathrm{state 1}}_{\mathrm{observed}} - \lambda^{\mathrm{state 2}}_{\mathrm{observed}}$ where $\lambda$ is the wavelength of the spectral peak of interest and $\lambda^{\mathrm{state 1}}_{\mathrm{observed}} > \lambda^{\mathrm{state 2}}_{\mathrm{observed}}$

For example, β-acylpyrrole will show a hypsochromic shift of 30-40 nm in comparison with α-acylpyrroles.

See also

• Bathochromic shift, a change in band position to a longer wavelength (lower frequency).