Inhomogeneous Quenching as a Limit of the Correlation Between Fluorescence Polarization and Conformation of Single Molecules.

The photophysical properties of conjugated polymers (CPs) largely depend on the interactions between the CP and its environment. We present a study of two polymers with identical conjugated backbones, bare and insulated, that showed different fluorescence excitation modulation depth histograms. However, the polarization differences are not related to differences in conformation, as commonly believed, but to the existence of "dark" chromophores in the bare polymer that are statically quenched. This results in inhomogeneous quenching of the polymer chain that breaks the correlation between excitation fluorescence polarization and conjugated polymer chain conformation.