Chromophoren

Chromophoren, or chromophores in English, are chemical substructures that absorb light in the visible or near-UV region and thereby impart color to a compound. They arise from electronic transitions within conjugated pi systems, lone-pair-containing groups, or metal-ligand interactions. The observed color results from the wavelengths of light not absorbed by the molecule, while surrounding factors such as solvents and pH can modulate the absorption.

Many organic chromophores are based on extended conjugation. Common examples include azo groups, carbonyl-containing conjugated systems, and polyenes. More complex chromophore cores such as porphyrins, seen in chlorophyll and heme, or the chromophore responsible for green fluorescence in GFP, derive their color from highly delocalized electronic structures. In inorganic chemistry, transition metal complexes produce vivid colors via d-d transitions or metal-to-ligand charge transfer.

The practical significance of chromophores spans dyes, pigments, and biological coloration. In spectroscopy, chromophores determine a compound’s absorption spectrum, summarized by the wavelength of maximum absorption (λmax) and molar extinction coefficient (ε). Solvent polarity, pH, and substituent electronics can shift λmax (bathochromic or hypsochromic shifts), altering color and detectability. Understanding chromophores supports applications in materials science, sensing, biology, and art conservation.