Question

Discuss other deactivation processes that compete with fluorescence.

Answer 1

Deactivation of the electronic excited state is also involved in phosphorescence . The molecule transition occur through intersystem crossing from the excited singlet state to triplet state . After this, further deactivation occurs through external fluorescence or phosphorescence.

A triplet-to-singlet transition is more probable than a singlet-to-triplet internal crossing.

In phosphorescence ,the excited state lifetime is inversely proportional to the probability that the molecule will transition back to the ground state.

Since the external and internal conversation compete so effectively with phosphorescence, the molecule has to be observed at lower temperature in highly viscous media to protect the triplet state.

Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs.

(Singlet excited Intersystem crossing state) Fluorescence - 3A (triplet) state Phosphorescence fir-E (Singlet ground my state)