Transcript Decay Curves of Pyrene

Fluorescence Lab
Julia Schmitz
CHEM 250
March 28, 2002
Frank-Condon Principle
What is Fluorescence?
How a LASER works
Our LASER
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Nitrogen Laser
¼ - meter monochromator
Digital oscilloscope
Computer-interfaced boxcar
Purpose of this Lab
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Record luminescence spectrum
Record Decay Curve
Investigate Quenching
Determine Lifetime
What is anthracene
• Aromatic hydrocarbon
• Easily excited at 337 nm
What is pyrene
• Absorbs strongly at wavelength of
Nitrogen Laser
• Fairly long excited-state lifetime
Calculating Energies
References
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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.
Fluorescence Spectra and Decay
Lifetimes
K. Nicole Crowder
March 28, 2002
Intermediate Lab 250
Absorption Spectrum of Anthracene
• This UV/Vis spectrum shows peaks at 324,
340, 356, and 376 nm.
Energies of Absorbance, in cm-1
Peaks
324
Energy for Energy for Energy for
+2 nm
nm
–2 nm
31056
30864
30675
340
29586
29412
29240
356
28249
28090
27933
376
26738
26596
26455
Fluorescence Spectrum of
Anthracene
• The spectrum shows absorbance at 386, 404,
428, and 456 nm.
Energies of Fluorescence, in cm-1
Peaks
386
Energy for Energy for Energy for
+2 nm
nm
–2 nm
26042
25907
25773
404
24876
24752
24631
428
23474
23364
23256
456
22026
21930
21834
Energy Spacing in Absorption vs.
Fluorescence Spectra
Peaks
Absorption
Fluorescence
1 to 2
1452
1155
2 to 3
1322
1388
3 to 4
1494
1434
Fluorescence Spectrum of 10-5M
Pyrene solution
• The fluorescence of pyrene was monitored
from at 350 to 500 nm.
Fluorescence Spectrum of 10-3M
Pyrene solution
• The same conditions were used for this new
concentration, although at 1 nm intervals.
Lifetime of the Excited State of
Anthracene and Pyrene
• What is the lifetime, t?
• For a first-order decay,
I = Io e
•This can also be expressed as
I = 0.37 Io.
•This is quite easy to measure.
kobst
Lifetime of Anthracene
Without N2
With N2
Lifetime of 10-5M Pyrene solution
Without N2
With N2
Lifetime of Monomer and Excimer in
10-3M Pyrene solution
Monomer
Excimer
Decay Curves of Pyrene
Courtney Arnott
March 28, 2002
CHEM 250
Data Collection
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N2 bubbled through sample
Measured fluorescence emission
Data collected in LabVIEW
What Order??
Points to consider…
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Export data into Excel
Plot curves
Line of best fit
Linear through several lifetimes!!
Wavelength = 387nm (for monomer)
Quenching
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
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
Zeroth Order Plot
First Order Plot
Second Order Plot
Conclusions?
• R2 Values
– 0th = .9455
– 1st = .9939
– 2nd = .8821
• Follows 1st order
decay curve
• Success!
Further Research
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Study other compounds suggested
Overcoming quenching with other gases
Examine phosphorescence
Look at monomer and excimer