When a singlet state nonradiatively passes to a triplet state, or conversely a triplet transitions to a singlet, that process is known as intersystem crossing.
22.
Where \ F is the fraction of particles that have entered the triplet state and \ \ tau _ F is the corresponding triplet state relaxation time.
23.
Where \ F is the fraction of particles that have entered the triplet state and \ \ tau _ F is the corresponding triplet state relaxation time.
24.
For phosphorescence, absorbed photons undergo intersystem crossing where they enter into a state with altered spin multiplicity ( see term symbol ), usually a triplet state.
25.
For example, the copper metallated octaethylbenzochlorin photosensitiser has a triplet state lifetime of less than 20 nanoseconds and is still deemed to be an efficient photodynamic agent.
26.
At room temperature, O 2 exists in a triplet state, which can only undergo a chemical reaction by making the forbidden transition into a singlet state.
27.
Excited organic molecules can also relax via conversion to a triplet state, which may subsequently relax via phosphorescence, or by a secondary non-radiative relaxation step.
28.
The singlet state is believed be more reactive than the ground state triplet state, in the same way that singlet oxygen is more reactive than the triplet oxygen.
29.
For example, a triplet transition quantum yield is the fraction of molecules that, after being photoexcited into a singlet state, cross over to the triplet state.
30.
An exciton formed by the recombination of two such particles may either be in a singlet state or a triplet state, depending on how the spins have been combined.
