Question

Question 5 (2 marks) (a) Explain the relationship between UV-Vis Spectroscopy and Fluorescence using the Riboflavin molecule shown below: 0.025 0.02 0.015 absorption CH Ads 0.005 fluorescence LOH 250350450550650750850 OH (b) Why must a molecule that fluoresces also have an absorption spectrum?

Answer 1

Question 5 (a) The uvrvis staat. spectrum and fluorescene Spectrum Share a mirror image relationship. This is a Corollary . of the Kasha?s rule 16 for a molecule i to fluoresce, electrons need to be promoted from so electronic state to higher electronic state from the lowest vibrational level I(vog of singly excited state (S1); fluoresence occurs. However, the Ab absooption spectroscopy involves I promotion of electrons from so to si. Thus; if the molecule is not una active, we can never know the excitation wavelength required to record fluoresco spectrum