Fluorescence Lab Julia Schmitz CHEM 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. Internet. Accessed 3/25/02http://omlc.ogi.edu/spectra/PhotochemCAD/html/anthracene.html Atkins, Peter. Physical Chemistry. W.H. Freeman and Company, New York, 6 th ed Van Dyke, D. A; Pryor, B. A.; Smith, P. G.; Topp, M. R. J. Chem. Educ. 1998, 75, 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, Van Dyke, D. A; Pryor, B. A.; Smith, P. G.; Topp, M. R. J. Chem. Educ. 1998, 75, 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.Van Dyke, D. A; Pryor, B. A.; Smith, P. G.; Topp, M. R. J. Chem. Educ. 1998, 75, Piepho, Susan. Laser Lab Handout. Instrumental Setup for LabVIEW-Controlled Fluorescence and Phosphorescence Experiments. March 11, 2002.Laser Lab Handout

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 PeaksEnergy for +2 nm Energy for nm Energy for –2 nm

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

Energies of Fluorescence, in cm -1 PeaksEnergy for +2 nm Energy for nm Energy for –2 nm

Energy Spacing in Absorption vs. Fluorescence Spectra PeaksAbsorptionFluorescence 1 to to to

Fluorescence Spectrum of M Pyrene solution The fluorescence of pyrene was monitored from at 350 to 500 nm.

Fluorescence Spectrum of M 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, This can also be expressed as I = 0.37 I o. This is quite easy to measure.

Lifetime of Anthracene Without N 2 With N 2

Lifetime of M Pyrene solution Without N 2 With N 2

Lifetime of Monomer and Excimer in M Pyrene solution Monomer Excimer

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

Data Collection N 2 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

Using molecular O 2 to accelerate breakdown of decay curve Can stop quenching with other gases Result? N 2 addition is significant W/O N 2 W/ N 2

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? R 2 Values –0 th =.9455 –1 st =.9939 –2 nd =.8821 Follows 1 st order decay curve Success!

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