Bathochromic shift (from Greek βαθύς bathys, "deep"; and χρῶμα chrōma, "color"; hence less common alternate spelling "bathychromic") 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 longer wavelength than most other colors, this effect is also commonly called a red 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 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.
- where is the wavelength of the spectral peak of interest and
- Hypsochromic shift, a change to shorter wavelength (higher frequency)