Purpose The purpose of this experiment is to determine the energy level diagram of anthracene using its absorption and fluorescence spectra, as well as the quantum yield and rate constant of fluorescence quenching of antracene by CCl4.

Methods A solution of anthracene and another solution of CCl4 are made in ethanol and mixed and diluted to various concentrations. The fluorescence and absorption spectra of these solutions are measured using a UV-visible spectrometer and a fluorescence spectrometer. Then a solution of anthracene is prepared in cyclohexane. Again, the fluorescence and absorption spectra are obtained and served as a reference for all calculations.

Procedure The procedure followed was given in the lab manual, Experiment 23, …show more content…
Then the spectra are normalized by making the intensities of the two closest peaks equal to one. This is achieve by dividing the all intensities by the intensity of the target peak. In addition, convert the wavelength (nm) to wavenumbers (cm-1), shown in Figure 4 and 5. Then determine the stokes shift in cm-1 by subtracting the difference in wavenumber between the lowest energy absorbance band and the highest energy fluorescence band. For calculations, refer to Appendix A. A Jablonski diagram in Figure 6 is created based on Figure 5, and it describes where each transition occurs. Next, the quantum yield of fluorescence for anthracene in ethanol was calculated using equation 23.4 in the lab manual, in which the A represents the absorption intensity of the target peaks and I represents the fluorescence intensity of the target peaks. For calculations, refer to Appendix B. Base on equation 23.13 in the lab manual, a plot of Ipure/IQ vs. [CCl4] was generated, shown in Figure 7. Ipure is obtained from the intensity of the left-most peak of solution 3 in Figure 3. IQ is obtained from all the intensities of the left-most peaks of solutions A through F. The slope of the fitted line equals to the value of k_Q/((k_f+k_nr)), in which kQ represents the fluorescence quenching rate