Delocalised Frenkel excitons

The almost instantaneous availability of the exciton energy over the whole of the conjugated sequence means that the collection of energy for passage to 

The general rule of thumb, then, is that polymeric materials are far more efficient light harvesters than small molecules in similar concentrations. Consequently, polymers are far more likely to undergo light initiated chemical reactions, such as oxidation or degradation, than are analogous small molecules. 

---

Excitation of the polymer creates one electron and a hole on the chain. This effect is particularly important when the electron-hole interactions are strong. Coulomb attraction keeps them together and we consider the two opposite charges as a bound electron-hole pair. An exciton (Fig. 1.11) is named according to its delocalisation. If it is localised, it is called a Frenkel exciton and, if it is delocalised, i.e., it extends over many molecular units, it is a Mott-Wannier type of exciton. ... 

When the electronic interaction between the chromophores along a polymer chain is so strong that the electrons may be delocalised over several cbromophores, the exciton may also be similarly delocalised. Such a delocalised exciton is called a Frenkel exciton. Frenkel excitons have been observed in conjugated polymers such as polyphenylacetylene (Figure 13.10). 

---