module: light & matterlesson: optical absorption 1 introduction to biophotonics optical...

Module: Light & MatterLesson: Optical Absorption

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Introduction to BiophotonicsIntroduction to Biophotonics

OPTICALABSORPTION


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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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LESSON OUTLINE

• Absorption/Transmittance;

• Photon Absorption;

– Franck-Condon Principle

– Absorption/Transmittance Spectra;

• Fate of Excited States


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© Thomson/Brooks Cole

Tunable Laser (x ) Sample

Detector

I0 (x )

L

It(x ) = I0 (x ) e-LIt(x ) = I0 (x ) e-L

= absorption coefficient

It(x )

TRANSMITTANCE


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ABSORPTION &

TRANSMISSIONSPECTRA

http://www.chem.ed.ac.uk/teaching/undergrad/chemistry1/lectures/notes/spectroscopy/spectroscopy%20lectures.pdf


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LESSON OUTLINE







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FRANCK-CONDON PRINCIPLE

http://www.csus.edu/indiv/m/mackj/chem140b/elecspec.pdf


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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.


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ABSORPTIONSTATES


As the optical transition becomes less vertical the absorption spectra shift due to the change in the Franck-Condon patterns.


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POTENTIAL ENERGY

CURVES FOR MOLECULAR

OXYGEN



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MOLECULAR

ORBITALS FOR

BENZENE

http://faculty.smu.edu/ebiehl/Wade16.ppt


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THE ABSORPTION SPECTRUM OF CHLOROPHYLL

Red

Blue

Green

http://www.nat.vu.nl/bio/images/fluorescence18062004_1.ppt


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TRANSMITTANCE - Aromatic Compounds -


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TRANSMITTANCE- Carbonyl Compounds -


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BROADENED ABSORPTION SPECTRA



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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.


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LESSON OUTLINE







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FATE OF EXCITED STATES(Primary Photochemical Processes)



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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


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DO YOU KNOW WHAT YOU KNOW?


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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:

module: light & matterlesson: optical absorption 1 introduction to biophotonics optical...

Documents

absorption coefficient

light matterlesson

continuous band of absorption

optical transition

t x transmittance slide

benzene http

molecular oxygen http

franckcondon patterns