In: Chemistry
Sketch potential energy curves for the ground and excited states showing events leading to phosphoresce. Use arrows to label all necessary transitions and answer the following:
A) Based on your picture does phosphoresce occur at lower or higher wavelength relative to the absorption wavelength?
B) Would you expect 0-0 transition for absorption and phosphorescence to be coincident?
A) Phosphorescence occut at higher wavelength (lower energy or lower frequency) relative to the absorption wavelength.
B) One transition, that from the lowest vibrational level in the ground electronic state to the lowest vibrational level in the first excited state, the 0 - 0 transition, is common to both the absorption and emission phenomena, whereas all other absorption transitions require more energy than any transition in the fluorescence emission. We can therefore expect the emission spectrum to overlap the absorption spectrum at the wavelength corresponding to the 0 - 0 transition and the rest of the emission spectrum to be of lower energy, or longer wavelength.
In practice, the 0-0 transitions in the absorption and emission spectra rarely coincide exactly, the difference representing a small loss of energy by interaction of the absorbing molecule with surrounding solvent molecules.