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Chemistry LibreTexts

3: Molecular Luminescence

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Learning Objectives

After completing this unit the student will be able to:

  • Describe the difference between a singlet and triplet state.
  • Draw an energy level diagram and identify the transitions that correspond to absorption, fluorescence, internal conversion, radiationless decay, intersystem crossing and phosphorescence.
  • Explain why phosphorescence emission is weak in most substances.
  • Draw a diagram that shows the layout of the components of a fluorescence spectrophotometer.
  • Describe the difference between a fluorescence excitation and emission spectrum.
  • Draw representative examples of fluorescence excitation and emission spectra.
  • Describe a procedure for measuring phosphorescence free of any interference from fluorescence.
  • Justify why fluorescence measurements are often more sensitive than absorption measurements.
  • Describe the meaning and consequences of self-absorption.
  • Identify variables including the effect of pH that can influence the intensity of fluorescence.
  • Identify the features that occur in organic molecules that are likely to have high fluorescent quantum yields.
  • Compare two molecules and determine which one will undergo more collisional deactivation.

Luminescent methods refer to a family of techniques in which excited state species emit electromagnetic radiation. Among luminescent methods are various sub-categories that include the processes of fluorescence, phosphorescence, chemiluminescence, bioluminescence and triboluminescence. Among these different sub-categories, fluorescence spectroscopy is by far the most common technique used for analysis purposes. You are no doubt familiar with fluorescent lights. This unit will allow you to understand how such a light works.

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This page titled 3: Molecular Luminescence is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Thomas Wenzel via source content that was edited to the style and standards of the LibreTexts platform.

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