421-821-chapter-15

421-821-chapter-15 - Fluorescence Phosphorescence...

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Fluorescence, Phosphorescence, A) Introduction 1.) Theory of Fluorescence and Phosphorescence : - Excitation of e - by absorbance of h ν . - Re-emission of h ν as e - goes to ground state. - Use h ν 2 for qualitative and quantitative analysis 10 -8 – 10 -9 s M* M + heat
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Fluorescence, Phosphorescence, A) Introduction 1.) Theory of Fluorescence and Phosphorescence : Method Mass detection limit (moles) Concentration detection limit (molar) Advantages UV-Vis 10 -13 to 10 -16 10 -5 to 10 -8 Universal fluorescence 10 -15 to 10 -17 10 -7 to 10 -9 Sensitive For UV/Vis need to observe P o and P difference, which limits detection For fluorescence, only observe amount of P L
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2.) Fluorescence – ground state to single state and back. Phosphorescence - ground state to triplet state and back. Spins paired No net magnetic field Spins unpaired net magnetic field Fluorescence Phosphorescence 0 sec 1 sec 640 sec Example of Phosphorescence
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3) Jablonski Energy Diagram 2 1 Resonance Radiation - reemission at same λ usually reemission at higher λ (lower energy) Numerous vibrational energy levels for each electronic state Forbidden transition : no direct excitation of triplet state because change in multiplicity –selection rules. 1
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4.) Deactivation Processes : a) vibrational relaxation : solvent collisions - vibrational relaxation is efficient and goes to lowest vibrational level of electronic state within 10 -12 s or less. - significantly shorter life-time then electronically excited state - fluorescence occurs from lowest vibrational level of electronic excited state, but can go to higher vibrational state of ground level. -
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421-821-chapter-15 - Fluorescence Phosphorescence...

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