Brent-Experiment 6

Brent-Experiment 6 - Experiment 6- Absorption and...

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Experiment 6- Absorption and Fluorescence Spectroscopy of Porphyrins and Metallo-Porphyrins Author: Brent G. Klapthor Group 6 Section 4, Tues 11:00 AM - 2:00 PM Partner: Jacob Waters 2/8/2011 Abstract: The first objective of this experiment consisted of obtaining the absorption spectrum of tetraphenylporphyrin H 2 TPP, ZnTPP, NiTPP, and TPP 2- by way of UV- visible light spectroscopy. A comparison of the wavelength energy required to produce the Soret band showed that in order of increasing energy the samples proceed TPP 2- , ZnTPP, H 2 TPP, and NiTPP. A comparison of the α/β intensity ratio for ZnTPP and NiTPP shows the ZnTPP sample producing a ratio 0.07 and the Ni sample having a ratio of 0.10. This indicates the a 2u and a 1u orbitals are closer to each other in energy in the zinc porphyrin. The second objective of this experiment focused on the creation of a fluorescence emission spectroscopy on these same samples. A comparison of the luminescence intensity shows TPP 2- having the greatest intensity followed by H 2 TPP and then ZnTPP with NiTPP hardly registering luminescence.
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Experiment 6- Absorption and Fluorescence Spectroscopy I. Introduction Porphyrins consist of an important class of organic molecules commonly found in nature. They are characterized as cyclic macromolecules with a diverse set of functions. The variety of metals capable of binding in the pocket of the porphyrin ring system to produce metallo-porphyrin compounds allows for this diversity. Their applications run from the highly important task of oxygen storage and transfer in blood to research in the fields of organic LEDs and photovoltaic cells. The objectives of this experiment consisted first of measuring the absorption spectrum of tetraphenylporphyrin H 2 TPP, ZnTPP, NiTPP, and TPP 2- by way of UV-visible light spectroscopy. The peak wavelengths and absorbances of each spectrum were noted and recorded. Each spectrum consisted of one major peak accompanied by a series of smaller peaks. The large peak, known as the Soret or B band, indicated a strong transition to the second excited state (S 0 →S 2 ). The subsequent smaller peaks, composing the Q bands, designated a weak transition to the first excited state (S 0 →S 1 ). According to the Gouterman Four-Orbital Model, the absorption bands in porphyrin systems arise from transitions between two degenerate or nearly degenerate HOMO orbitals and two LUMO orbitals. The identities of the metal center and substituent on the ring affect the relative energies of these transitions. Mixing splits these two states in energy, creating a higher energy 1 eu state with greater oscillator strength, giving rise to the Soret band, and a lower energy 1 eu state with less oscillator strength, giving rise to the Q-bands. Once the UV-Visible Spectrum was taken for the DMF solutions of H
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This note was uploaded on 03/08/2011 for the course CHEM 232 taught by Professor James during the Spring '11 term at Clemson.

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Brent-Experiment 6 - Experiment 6- Absorption and...

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