In this experiment, Students synthesize a Schiff Base and the corresponding aluminum complex to measure fluorescence. The lab provides exposure to air-free synthetic techniques, including the use of Schlenk Line techniques and safe handling of sure-seal bottles. Following data collection, students will be able to explain fluorescence spectroscopy and compare it to absorbance spectroscopy.
Following this experiment, a student will be able to:
• Utilize Schlenk-line techniques to perform an air-free synthesis
• Synthesize Schiff Base ligands through an imine condensation of aldehydes with primary amines.
• Prepare UV-Vis samples to determine max for an organometallic complex.
• Calibrate and operate a Fluorimeter to gain absorption and emission spectra.
• Explain the difference between absorbance measurements in a UV-Vis experiment and excitation/emission spectra from the Fluorimeter.
• Calculate the Stokes Shift for a fluorescent process.
Safely Handle Pyrophoric Solutions (Sure-Seal Bottles)
Provide a careful overview of how to use a Sure-Seal bottle safely!
The synthesis of the Schiff Base ligands (SOAP used in this experiment, SALEN is used in a later experiment) is done during the characterization period for the previous experiment.
Students work in pairs, and divide the Schiff Base ligands among themselves and then work together on the Aluminum Complex Synthesis.
This lab is preceded by a lecture on fluorescence and the operation of a fluorimeter.
Check the calculations for the dilutions for the Fluorimeter measurements. They should do sequential dilutions, otherwise they waste 500 mL of solvent if they aren't careful.
Each experiment results in a report, written in the style of an ACS publication, that includes an introduction, results and discussion, and conclusion sections along with a supporting information. The “Discussion Questions” are to lead students through constructing the Results and Discussion section of the report.
This experiment is generally one of the higher scoring reports, as the analysis is relatively straightforward. In a survey at the end of the quarter, this experiment was listed as the favorite for 2 students out of 19 (8 experiments total).
A common misconception is students thinking that the excitation scans in the Fluorimeter are the same as the UV-Vis absorbance data, due to the similarity in the way the spectrum looks.
When calculating the Stokes Shift, some students will use a difference in wavelength instead of a difference in the energy. This comes from a misunderstanding of the relationship between wavelength and energy.