Nonlinear optical properties of conjugated polymers

This manuscript reports that conjugated polymers can show a significant hyperpolarizability, as measured by hyper- Rayleigh scattering (HRS). First, a disubstituted poly(phenanthrene) is examined. It is shown that the polymer exhibits an unexpected, but extremely large second-order nonlinear optical (NLO) response, which moreover strongly depends on the solvent conditions. As the molecular structure of the polymer does not at all fit into the classical paradigms, but yet an extremely high hyperpolarizability is measured, these observations put these theories into perspective. An explanation is postulated, which is based on the variation of the conjugation. Second, the hyperpolarizability of regioregular HTcoupled poly(3-hexylthiophene)s (HT-P3HT)s is measured. It is found that also this conjugated polymer shows a significant hyperpolarizability, showing that the observed NLO behavior of conjugated polymers is not restricted to one polymer, but is instead more general. The dependency of the hyperpolarizability on the degree of polymerization is established.