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Fluorescence Lab

Fluorescence Lab

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Fluorescence Lab

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  1. Fluorescence Lab Julia Schmitz CHEM 250 March 28, 2002

  2. Frank-Condon Principle

  3. What is Fluorescence?

  4. How a LASER works

  5. Our LASER • Nitrogen Laser • ¼ - meter monochromator • Digital oscilloscope • Computer-interfaced boxcar

  6. Purpose of this Lab • Record luminescence spectrum • Record Decay Curve • Investigate Quenching • Determine Lifetime

  7. What is anthracene • Aromatic hydrocarbon • Easily excited at 337 nm

  8. What is pyrene • Absorbs strongly at wavelength of Nitrogen Laser • Fairly long excited-state lifetime

  9. Calculating Energies

  10. References • Anthracene. http://omlc.ogi.edu/spectra/PhotochemCAD/html/anthracene.html. Internet. Accessed 3/25/02 • Atkins, Peter. Physical Chemistry. W.H. Freeman and Company, New York, 6th ed. 1998. • Van Dyke, D. A; Pryor, B. A.; Smith, P. G.; Topp, M. R. J. Chem. Educ. 1998, 75, 615-620. Nanosecond Time-Resolved Fluorescence Spectroscopy in the Physical Chemistry Laboratory: Formation of the Pyrene Excimer in Solution. • Van Dyke, D. A; Pryor, B. A.; Smith, P. G.; Topp, M. R. J. Chem. Educ. 1998, 75, 615-620. Nanosecond Time-Resolved Fluorescence Spectroscopy in the Physical Chemistry Laboratory: Formation of the Pyrene Excimer in Solution. Journal of Chemical Education. Vol 75. No 5. May 1998. • Piepho, Susan. Laser Lab Handout. Instrumental Setup for LabVIEW-Controlled Fluorescence and Phosphorescence Experiments. March 11, 2002.

  11. Fluorescence Spectra and Decay Lifetimes K. Nicole Crowder March 28, 2002 Intermediate Lab 250

  12. Absorption Spectrum of Anthracene • This UV/Vis spectrum shows peaks at 324, 340, 356, and 376 nm.

  13. Energies of Absorbance, in cm-1

  14. Fluorescence Spectrum of Anthracene • The spectrum shows absorbance at 386, 404, 428, and 456 nm.

  15. Energies of Fluorescence, in cm-1

  16. Energy Spacing in Absorption vs. Fluorescence Spectra

  17. Fluorescence Spectrum of 10-5M Pyrene solution • The fluorescence of pyrene was monitored from at 350 to 500 nm.

  18. Fluorescence Spectrum of 10-3M Pyrene solution • The same conditions were used for this new concentration, although at 1 nm intervals.

  19. Lifetime of the Excited State of Anthracene and Pyrene • What is the lifetime, t? • For a first-order decay, • This can also be expressed as • I = 0.37 Io. • This is quite easy to measure.

  20. Lifetime of Anthracene Without N2 With N2

  21. Lifetime of 10-5M Pyrene solution Without N2 With N2

  22. Lifetime of Monomer and Excimer in 10-3M Pyrene solution Monomer Excimer

  23. Decay Curves of Pyrene Courtney Arnott March 28, 2002 CHEM 250

  24. Data Collection • N2 bubbled through sample • Measured fluorescence emission • Data collected in LabVIEW • What Order??

  25. Points to consider… • Export data into Excel • Plot curves • Line of best fit • Linear through several lifetimes!! • Wavelength = 387nm (for monomer) • Quenching

  26. Quenching W/O N2 W/ N2 • Using molecular O2 to accelerate breakdown of decay curve • Can stop quenching with other gases • Result? N2 addition is significant

  27. Monomer vs. Excimer • Monomer – excited molecule • Excimer – excited dimer • Varies with concentration Figure from Van Dyke et.al, JChemEd Vol 75 No 5 p. 618

  28. Zeroth Order Plot

  29. First Order Plot

  30. Second Order Plot

  31. Conclusions? • R2 Values • 0th = .9455 • 1st = .9939 • 2nd = .8821 • Follows 1st order decay curve • Success!

  32. Further Research • Study other compounds suggested • Overcoming quenching with other gases • Examine phosphorescence • Look at monomer and excimer