The energies of photons in the ultraviolet and visible region of the spectrum correspond to the separation of electronic energy levels in molecules and atoms. Absorption in the visible/ultraviolet can occur if two criteria are met:

Quantitative analysis of solutions

Ultraviolet absorption is often used to determine the concentration (via Beer's Law) of dilute solutions of polymers that contain chromophores. This use requires knowledge of the value of the extinction coefficient for that polymer in the solvent being used for the measurement. It can also be used to monitor kinetic processes in which a chromophore is created or destroyed, or in which a chromophore changes state. For example, ionization of a phenol, as in poly(4-vinylphenol), is accompanied by a red shift of the absorption and a strong increase in the value of the extinction coefficient.

Quantitative analysis of conformational change

Ordered arrays of identical (or similar) chromophores often have different values of the extinction coefficient than do random arrays of the same chromophores.

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July 6, 1999
Wayne L. Mattice: wlm@polymer.uakron.edu