Fluorescence Lab

Julia SchmitzCHEM 250

March 28, 2002

Frank-Condon Principle

What is Fluorescence?

How a LASER works

Our LASER

• Nitrogen Laser• ¼ - meter monochromator• Digital oscilloscope• Computer-interfaced boxcar

Purpose of this Lab

• 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• 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 CrowderMarch 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 Energy for +2 nm

Energy for nm

Energy for –2 nm

324 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 Energy for +2 nm

Energy for nm

Energy for –2 nm

386 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, ?• For a first-order decay, I = Io e

kobst

•This can also be expressed as I = 0.37 Io.

•This is quite easy to measure.

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 ArnottMarch 28, 2002

CHEM 250

Data Collection

• N2 bubbled through sample

• Measured fluorescence emission• Data collected in LabVIEW• What Order??

Points to consider…

• Export data into Excel• Plot curves• Line of best fit• Linear through several lifetimes!!• Wavelength = 387nm (for

monomer)• Quenching

Quenching

• Using molecular O2 to accelerate breakdown of decay curve

• Can stop quenching with other gases

• Result? N2 addition is significant

W/O N2 W/ N2

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

• Study other compounds suggested• Overcoming quenching with other

gases• Examine phosphorescence• Look at monomer and excimer