Fluorescence Lab Julia Schmitz CHEM 250 March 28, 2002
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
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 Crowder March 28, 2002 Intermediate Lab 250
Absorption Spectrum of Anthracene • This UV/Vis spectrum shows peaks at 324, 340, 356, and 376 nm.
Fluorescence Spectrum of Anthracene • The spectrum shows absorbance at 386, 404, 428, and 456 nm.
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, • 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 Arnott March 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 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
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