hypsochromic shift

{{short description|Change in a molecule's spectral band position to a shorter wavelength}}

{{More sources needed|date=December 2009}}

In spectroscopy, hypsochromic shift ({{ety|grc|ὕψος (upsos)|height||χρῶμα (chrōma)|color}}) 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.{{Cite web |title=Illustrated Glossary of Organic Chemistry - Bathochromic shift, hypsochromic shift; red shift; blue shift |url=https://www.chem.ucla.edu/~harding/IGOC/B/bathochromic_shift.html#:~:text=A%20hypsochromic%20shift%20is%20the,as%20450%20nm%20is%20hypsochromic. |access-date=2024-11-11 |website=www.chem.ucla.edu}} It should not be confused with a bathochromic shift, which is the opposite process – the molecule's spectra are changed to a longer wavelength (lower frequency).

Hypsochromic shifts 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.

:$\backslash Delta\backslash lambda\; =\; \backslash lambda\backslash !\_\{\backslash text\{state\; 1\}\; \backslash atop\; \backslash text\{observed\}\}\; -\; \backslash ,\; \backslash lambda\backslash !\_\{\backslash text\{state\; 2\}\; \backslash atop\; \backslash text\{observed\}\}$

where $\backslash lambda$ is the wavelength of the spectral peak of interest and $\backslash lambda\backslash !\_\{\backslash text\{state\; 1\}\; \backslash atop\; \backslash text\{observed\}\}\; >\; \backslash ,\; \backslash lambda\backslash !\_\{\backslash text\{state\; 2\}\; \backslash atop\; \backslash text\{observed\}\}\backslash !.$

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