Intersystem crossing

Intersystem crossing (ISC) is an isoenergetic radiationless process involving a transition between the two electronic states with different spin multiplicity.

The probability of this process occurring is more favorable when the vibrational levels of the two excited states overlap, since little or no energy must be gained or lost in the transition.

Another species can then react with the long-lived excited state via oxidation or reduction, thereby initiating a redox pathway via tunable photoexcitation.

Complexes containing high atomic number d6 metal centers, such as Ru(II) and Ir(III), are commonly used for such applications due to them favoring intersystem crossing as a result of their more intense spin-orbit coupling.

[8] The viability of organometallic polymers in bulk heterojunction organic solar cells has been investigated due to their donor capability.

The efficiency of charge separation at the donor-acceptor interface can be improved through the use of heavy metals, as their increased spin-orbit coupling promotes the formation of the triplet MLCT excited state, which could improve exciton diffusion length and reduce the probability of recombination due to the extended lifespan of the spin-forbidden excited state.

Improved charge separation efficiency has been shown to be a result of the formation of the triplet excited state in some conjugated platinum-acetylide polymers.

Based upon this research, Gilbert Lewis and coworkers, during their investigation of organic molecule luminescence in the 1940s, concluded that this metastable energy state corresponded to the triplet electron configuration.