Pre-Assignment

1. What are the spin multiplicity and the spin of triplet state?
2. Why two electrons are always present in two different orbitals of the molecule in triplet state?
3. Internal conversion (takes place at a time scale of 10-12 s) is faster than the fluorescence emission. Then how does radiative emission (fluorescence) compete with the non-radiative transition? (Hint: Significantly larger energy gap between S1 and S0 and longer lifetime of S1.)
4. Transitions between states of different multiplicity are formally forbidden. What are the mechanisms that make the intersystem crossing probable?
5. How can you justify that the relaxation to ground state occurs via "vertical" transition?
6. In most of the cases, the S1 potential energy curve shifts to the right with respect to S0 potential energy curve. Justify it. (Hint: In the excited state, the electron is promoted to an anti-bonding orbital.)

Post-Assignment

1. What happens in Stokes shift: The fluorescence light is red-shifted (shifts to longer wavelength than the excitation light) or blue-shifted relative to the absorbed light?
2. How does the solvent effect affect the magnitude of the Stokes shift?
3. Why is the same fluorescence emission wavelength observed irrespective of the excitation wavelength?
4. Vibrational levels of which of the electronic states - electronic ground state or electronically excited state - are reflected by an emission spectrum?
5. "The detection of a fluorescent molecule becomes easier when the Stokes shift is larger." Why?
6. Do both the fluorophores obey the mirror image rule and why?
7. Which of the two fluorophores has larger area of overlapping region between the absorption and emission spectra? (Note: The overlapping region relates to the auto-absorption in inner filter effects.)