Chromophore
Introduction
A chromophore is a molecular fragment that absorbs certain wavelengths of visible light and gives a compound its color. The term chromophore was coined by the German chemist, Wilhelm Ostwald, to denote the group of atoms in a molecule responsible for its color characteristics. Chromophores are a central concept in molecular spectroscopy, particularly in infrared and UV/Vis spectroscopy.
Structure and Properties
Chromophores are composed of conjugated systems of double bonds or aromatic rings, and their color arises from the absorption of certain wavelengths of light. The energy difference between the absorbed light and the emitted light is known as the Stokes shift. The size of the Stokes shift can provide information about the environment of the chromophore.
Types of Chromophores
There are several types of chromophores based on the chemical structure and the type of light absorption. These include polyenes, cyanines, and retinal chromophores. Each type of chromophore has unique properties and applications.
Mechanism of Color Production
The color of a chromophore depends on the energy difference between its ground state and its excited state, which corresponds to a specific wavelength of light. When a chromophore absorbs light, it transitions from the ground state to an excited state. The energy difference between these states determines the wavelength of light absorbed, and hence the color of the chromophore.
Applications
Chromophores have a wide range of applications in various fields such as dyes, pigments, fluorescent probes, and photosensitizers. They are also essential components in biological systems, such as in chlorophyll for photosynthesis and in vision for the detection of light.