Interchain exciton

In summary, over a large range of interchain distances, the most stable species photogenerated in the lowest excited stale of clusters formed by identical molecules are excitons mostly with an intrachain character. The calculations also show that po-laron-pairs, also referral to as interchain excitons (corresponding to a positive polar-... 

The role of disorder in the photophysics of conjugated polymers has been extensively described by the work carried out in Marburg by H. Bassler and coworkers. Based on ultrafast photoluminescence (PL) (15], field-induced luminescence quenching [16J and site-selective PL excitation [17], a model for excited state thermalizalion was proposed, which considers interchain exciton migration within the inhomogenously broadened density of states. We will base part of the interpretation of our results in m-LPPP on this model, which will be discussed in some detail in Sections 8.4 and 8.6. 

We assume that the stationary electronic states are the eigenstates of the approximate Hamiltonian, Ho- Thus, the perturbation, Hj, mixes these electronic states. In particular, it causes an interconversion from the interchain excitons (or weakly bound polaron pairs) to the intrachain excitons. 

Since the lowest energy interchain excitons have even electron-hole parity this implies that H connects them to Sx and Tx, and not to the intramolecular S ct and Moreover, since the interchain exciton will have relaxed to its lowest... 

The absorption spectra of the copolymers exhibit two major absorption bands at 312-321 nm and 640 nm. These are reported to be due to the n-n transition associated with the conjugation of phenyl rings, and the intrachain/interchain exciton transition, respectively (Figure 20.51). The latter band is blue shifted upon increasing the anthranilic acid content, from which it is inferred that steric effects due to the presence of pendent carboxylic acid perturbs the 7r-electron system and lowers the degree of conjugation. 

A second area of disagreement centers around photoluminescence quenching at high excitation densities in thin films. The formation of nonradiative interchain polarons [1237, 1238] and interchain exciton formation [1239] have been proposed as sources responsible for the quenching mechanism. At moderately high excitation densities, bimolecular decay, resulting from interchain interactions between the excited species, is considered to be responsible for the fast photoluminescence decay [1240-1243]. At high excitation conditions, the formation of biexcitons becomes favored [1244,1245]. 

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