Intersystem Crossing

Intersystem crossing (ISC, engl. ) Is a term used in photochemistry and spectroscopy. It refers to the transition of an electron from an electronically excited energy level in a vibrationally, electronically excited energy level, which runs under spin reversal. The transition is thus radiationless. An example of which is the transition from the singlet to the triplet state (S ↔ T).

The dominant mechanism for the ISC in organic molecules is the interaction between the magnetic moment of the spin and the orbital of the atom ( ' spin-orbit coupling). In diradicals also the direct interaction between two spins is possible (spin -spin coupling ).

An intersystem crossing takes place before a phosphorescence.