Bathochromic shift

Bathochromic shift is a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a longer wavelength (lower frequency).

Because the red color in the visible spectrum has a higher wavelength than most other colors, this effect is also commonly called a red shift, although this usage is considered informal, and has no relation to Doppler shift or other wavelength-independent meanings of redshift. This usage is often found in the scientific literature.

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 bathochromic shift. Bathochromic 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.

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

Bathochromic shift is typically demonstrated using a spectrophotometer, colorimeter, or spectroradiometer.

See also

• Hypsochromic shift, a change to shorter wavelength (higher frequency)