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Intersystem crossing (ISC) is an isoenergetic radiationless process involving a transition between the two electronic states with different spin multiplicity. [ 1 ] Excited electrons can undergo intersystem crossing to a degenerate state with a different spin multiplicity.
A Jablonski diagram showing the excitation of molecule A to its singlet excited state (1 A*) followed by intersystem crossing to the triplet state (3 A) that relaxes to the ground state by phosphorescence. It was used to describe absorption and emission of light by fluorescents.
Jablonski diagram indicating intersystem crossing (left) and internal conversion (right). Internal conversion is a transition from a higher to a lower electronic state in a molecule or atom. [ 1 ] It is sometimes called "radiationless de-excitation", because no photons are emitted.
However, sustained excitation is followed by intersystem crossing to the triplet state (3 A) that relaxes to the ground state by phosphorescence with much longer decay times. In simple terms, phosphorescence is a process in which energy absorbed by a substance is released relatively slowly in the form of light.
By absorbing nearby thermal energy, the triplet state can undergo reverse intersystem crossing (RISC) converting the triplet state population to an excited singlet state, which then emits light to the singlet ground state in a delayed process termed delayed fluorescence. Accordingly, in many cases, the TADF molecules show two types of emission ...
Triplet states typically have longer lifetimes than excited singlets. The prolonged lifetime increases the probability of interacting with other molecules nearby. Photosensitizers experience varying levels of efficiency for intersystem crossing at different wavelengths of light based on the internal electronic structure of the molecule. [2] [7]
The sensitizer then populates its first triplet excited state (3 Sen*) after intersystem crossing (ISC). The excitation energy on the sensitizer then transfers through a Dexter type triplet energy transfer (TET) to a ground state emitter, generating a triplet excited emitter (3 Em*). Two triplet excited emitters then interact in a second energy ...
Non-radiative processes are excited state decay mechanisms other than photon emission, which include: Förster resonance energy transfer, internal conversion, external conversion, and intersystem crossing. Thus, the fluorescence quantum yield is affected if the rate of any non-radiative pathway changes.