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Module: Light & MatterLesson: Optical Absorption 1 Introduction to Biophotonics OPTICAL ABSORPTION.

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Presentation on theme: "Module: Light & MatterLesson: Optical Absorption 1 Introduction to Biophotonics OPTICAL ABSORPTION."— Presentation transcript:

1 Module: Light & MatterLesson: Optical Absorption 1 Introduction to Biophotonics OPTICAL ABSORPTION

2 Module: Light & MatterLesson: Optical Absorption 2 Introduction to Biophotonics LEARNING OBJECTIVES Describe photon absorption; Explain the basic principles that create an absorption spectra; Explain a broaden absorption spectra; Describe the possible fate of optically excited states; Each student should be able to:

3 Module: Light & MatterLesson: Optical Absorption 3 Introduction to Biophotonics LESSON OUTLINE Absorption/Transmittance; Photon Absorption; –Franck-Condon Principle –Absorption/Transmittance Spectra; Fate of Excited States

4 Module: Light & MatterLesson: Optical Absorption 4 Introduction to Biophotonics © Thomson/Brooks Cole Tunable Laser ( x ) Sample Detector I 0 ( x ) L I t ( x ) = I 0 ( x ) e -  L  = absorption coefficient I t ( x ) TRANSMITTANCE

5 Module: Light & MatterLesson: Optical Absorption 5 Introduction to Biophotonics ABSORPTION & TRANSMISSION SPECTRA

6 Module: Light & MatterLesson: Optical Absorption 6 Introduction to Biophotonics LESSON OUTLINE Absorption/Transmittance; Photon Absorption; –Franck-Condon Principle –Absorption/Transmittance Spectra; Fate of Excited States

7 Module: Light & MatterLesson: Optical Absorption 7 Introduction to Biophotonics FRANCK-CONDON PRINCIPLE

8 Module: Light & MatterLesson: Optical Absorption 8 Introduction to Biophotonics ABSORPTION SPECTRA When absorption occurs to unbound states of the upper electronic state, the molecule dissociates and the absorption is a continuum. Below the dissociate limit the electronic spectrum shows a normal vibrational structure. Above the dissociation limit a continuous band of absorption occurs because the final state is an un-quantized translation of the fragments.

9 Module: Light & MatterLesson: Optical Absorption 9 Introduction to Biophotonics ABSORPTION STATES As the optical transition becomes less vertical the absorption spectra shift due to the change in the Franck-Condon patterns.

10 Module: Light & MatterLesson: Optical Absorption 10 Introduction to Biophotonics POTENTIAL ENERGY CURVES FOR MOLECULAR OXYGEN

11 Module: Light & MatterLesson: Optical Absorption 11 Introduction to Biophotonics MOLECULAR ORBITALS FOR BENZENE

12 Module: Light & MatterLesson: Optical Absorption 12 Introduction to Biophotonics THE ABSORPTION SPECTRUM OF CHLOROPHYLL Red Blue Green

13 Module: Light & MatterLesson: Optical Absorption 13 Introduction to Biophotonics TRANSMITTANCE - Aromatic Compounds -

14 Module: Light & MatterLesson: Optical Absorption 14 Introduction to Biophotonics TRANSMITTANCE - Carbonyl Compounds -

15 Module: Light & MatterLesson: Optical Absorption 15 Introduction to Biophotonics BROADENED ABSORPTION SPECTRA

16 Module: Light & MatterLesson: Optical Absorption 16 Introduction to Biophotonics CHROMOPHORES Chromophores are a group of atoms in a molecule that produces color in dyes and other compounds through selective absorption of light, for example, the azo group. Chromophores are components of molecules which absorb light. The wavelength of absorption is related to the size of the chromophores. Smaller chromophores, higher energy (shorter wavelength). They are generally aromatic rings.

17 Module: Light & MatterLesson: Optical Absorption 17 Introduction to Biophotonics LESSON OUTLINE Absorption/Transmittance; Photon Absorption; –Franck-Condon Principle –Absorption/Transmittance Spectra; Fate of Excited States

18 Module: Light & MatterLesson: Optical Absorption 18 Introduction to Biophotonics FATE OF EXCITED STATES (Primary Photochemical Processes)

19 Module: Light & MatterLesson: Optical Absorption 19 Introduction to Biophotonics PREDISSOCIATION Predissociation is the relaxation to a state with enough energy to break a bond. Predissociation arises when two electronic states cross. Usually one electronic state is stable, and has a well defined potential diagram. The other state is typically a repulsive state. The transition is initially to the stable state, and then transfers across to the repulsive state, where dissociation occurs

20 Module: Light & MatterLesson: Optical Absorption 20 Introduction to Biophotonics DO YOU KNOW WHAT YOU KNOW?

21 Module: Light & MatterLesson: Optical Absorption 21 Introduction to Biophotonics LEARNING OBJECTIVES Describe photon absorption; Explain the basic principles that create an absorption spectra; Explain a broaden absorption spectra; Describe the possible fate of optically excited states; Each student should be able to:


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