Triplet Formation by Charge Transfer

As we have seen in Chapter 3, there is at least one triplet state below the first excited singlet state in the Franck-Condon region. The triplet is formed by reversing spin on the excited electron. It is lower than the corresponding singlet state by 2 K, where Kij is defined as 

We assume that the CT state is stable. Since Ky is small in this state, the singlet and triplet have almost equal energy. The mixing of spin in the two states with Ms equal to zero [Si(CT) and Ti(CT,Ms = 0)] is therefore quite large. 

FIGURE 13.3 Intersystem crossing induced by charge transfer (photochemically induced dynamic nuclear polarization [photo-CIDNP]). The arrows indicate the CIDNP pathway. The fnll-drawn line from the charge-separated state ends on the local triplet and the dashed line on the ground state. 

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