Development of an undergraduate experiment in fluorescence lifetime quenching using an improved pulsed LED photon source

CHED 395

Christopher M. Zall, zallk@carleton.edu, Steven M. Drew, sdrew@carleton.edu, and William E. Hollingsworth. Department of Chemistry, Carleton College, 1 N. College St., Northfield, MN 55057
Fluorescence quenching measurements are valuable as undergraduate physical chemistry experiments, as they examine the interface between spectroscopy and kinetics. Intermolecular interactions and photoelectronic properties of molecules can be studied simultaneously and interdependently. The measurement of fluorescence lifetime provides a means of probing the quenching interaction which is independent of excitation or detection efficiencies and is tolerant of changes in instrumental setup and alignment. However, the common use of a laser as an excitation source makes measurement of lifetimes relatively expensive and complex for implementation in large undergraduate laboratories. A method for generating pulsed excitation light using an LED has been described in the measurement of fluorescence quenching by O2 (Rusak et al., J. Chem. Edu. 2006, 83, 1857-1859). We have built an improved LED-based apparatus for the measurement of fluorescence lifetime quenching. The system has been used to study the Fe3+-quenched fluorescence of Ru(II)tris-bipyridine.