Estimate of the interconversion rates

Since interconversion from the intermolecular to the intramolecular charge-transfer excitons is forbidden by symmetry, we now only discuss interconversion to the 

Within the Mott-Wannier basis the exciton wavefunction overlaps are easy to calculate. Using tj =0.1 eV, the interchain distance as 4 A and standard semiempirical Coulomb interactions gives 

The ISC rate is also not accurately known, with quoted values ranging from 0.3 ns (Burin and Ratner 1998) to 4 ns (Frolov et al. 1997). Nevertheless, despite this uncertainty, we see that the estimated triplet interconversion rate is comparable to or slower than the ISC rate, which from eqn (9.112) and Fig. 9.11 implies a large singlet exciton yield 

This ratio increases as 5p decreases, because then multiphonon emission becomes more difficult. The ratio also increases as the exchange energy, ut — i s)huj, increases for any i s or vt ii Sp .  

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