We studied the absorption line-shape of poly(p-phenylenevinylene) (PPV) films deposited via spin coating and Langmuir-Blodgett techniques with the intent of identifying the conjugation length distribution in these two types of films, a key morphological aspect of conjugated polymer films. We treated the excitons in the polymer as independent oligomer excitons and modeled the absorption spectra of the individual oligomers using simple expressions for the oligomer size dependence of the gap energy, the line-broadening factor, the transition dipole moment and the Huang-Rhys parameter. We validated these expressions by independent measurements on phenyl-based oligomers and Density Functional Theory calculations. Our results show clear evidence that, for both types of PPV films, the conjugation length distribution depends exponentially on the segment size. Our results also set a lower limit, of about ten repeat units, for the maximum exciton length of three different phenyl-based oligomers.

The distribution of segment sizes, that is, the average and dispersion of the number of segments of a given size per chain, is investigated in an ensemble of lattice polymers. This distribution is the lattice version of the conjugation length distribution of conjugated polymers, which is central for both electronic and photophysical properties of conjugated polymer materials. Clear evidence is found that, when the chains interact only via excluded volume, both the average and the dispersion depend exponentially on the segment size and, at least for the more prevalent segment sizes, are identical to what is found in an isolated self‐avoiding chain. Whereas the polymer concentration has a clear effect on the end‐to‐end distances of the chains, it does not affect significantly the segment size distribution of the chains. It is argued that this happens whenever there is no distance or orientation correlation in the polymer distribution, that is, in a truly amorphous system, but not in the presence of aggregates or nematic order.

Front Cover: The distribution of straight segment lengths in an amorphous lattice polymer ensemble is highly insensitive to the polymer density and very similar to the distribution found in non‐reversal self‐avoiding random walks. This is reported by Joniel C. F. Alves and José A. Freire in article number https://doi.org/10.1002/mats.201800020.