Kromoforu

Kromoforu, commonly referred to in English as chromophore, is the part of a molecule that is primarily responsible for color by absorbing light. In chemistry, chromophores are typically associated with conjugated pi-electron systems or certain functional groups that can undergo electronic transitions, such as pi to pi or n to pi transitions, when they interact with visible or near-UV light.

The color arises because the absorbed wavelengths are removed from the spectrum of visible light, and the color seen is the complementary color of the absorbed light. The exact wavelengths absorbed—and thus the observed color—depend on the specific structure, including the extent of conjugation, molecular geometry, and the presence of electron-donating or electron-withdrawing substituents. Auxiliary substituents can shift absorption via bathochromic (red) or hypsochromic (blue) shifts, affecting the hue.

Common chromophores include azo groups (-N=N-), carbonyl-containing systems (such as ketones and aldehydes), extended conjugated dienes and polyenes, porphyrin rings, and cyanine chains. Many natural pigments (such as chlorophyll) and synthetic dyes rely on chromophoric structures to produce their characteristic colors.

In practice, chromophores are central to dyes, pigments, indicators, and various optical applications. They also feature in spectroscopy, where a molecule’s chromophore determines its UV-Vis absorption profile. Related terms include chromogen, which refers to a compound capable of forming a chromophore under certain conditions, and auxochrome, a substituent that modulates absorption without itself acting as the primary chromophore.