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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Chromophore

The part of a molecule that absorbs light and so gives it its colour (or its UV absorption); in this course, the conjugated π system. The longer the conjugated chromophore, the smaller its HOMO–LUMO gap and the longer the wavelength it absorbs.

Azobenzene: two benzene rings conjugated through N=N.

Example

In azobenzene the chromophore is the whole conjugated system, two benzene rings joined by N=N with 14 π electrons. It absorbs blue light (λmax⁡\lambda_{\max} ≈ 440 nm) and looks orange-yellow.

See alsoConjugationλmax (wavelength of maximum absorption)Complementary colourHOMO–LUMO gap