Charged photoexcitations

MEH-PPV and P3MBET, were used. As a measure of the efficiency of the photo-induced charge transfer, the degree of luminescence quenching and the ratio of the charged photoexcitation bands to the neutral photoexcitation bands were taken. These two numbers are plotted in Figure 15-15 versus the electrochemical reduction potential. A maximum in the photoinduced electron transfer was determined for Cbo. 

In order to study the charged photoexcitations in conjugated materials in detail their contribution to charge transport can be measured. One possible experiment is to measure thermally stimulated currents (TSC). Next, we will compare the results of the TSC-experiments, which are sensitive to mobile thermally released charges trapped after photoexcitation, to the temperature dependence of the PIA signal (see Fig. 9-17) which is also due to charged states as discussed previously. 

PIA bands appear in the near IR at around < 0.8 eV which shift to the red on increasing the chain length. The near IR absorption at around 0.8 eV and the shoulder at 1.5 eV (especially visible in six membered and seven membered oligothiophene 6T and 7T, Figure 8.35) are the charged photoexcitations on the oligomer backbone. 

Mixing Cgo into the oligothiophene solutions in ODCB quenches the photoinduced triplet-triplet absorption bands and enhances the charged photoexcitations. The two PIA bands associated with the radical cationic absorptions of the oligthiophenes dominate the... 

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