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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.

    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; a detailed edit history is available upon request.