Conformation and physics of polymer chains: a single-molecule perspective

Single-molecule optical detection and spectroscopy has emerged in recent years as an excellent tool for structural and dynamic characterization of materials and biological systems on nanometer scales. Measuring light emitted by individual molecules reveals static and dynamic heterogeneities that are otherwise hidden in the ensemble average. The removal of ensemble averaging is especially important in the study of polymers, where the complexity of the system is a result of the large size of individual molecules, of the distribution of their molecular weights, and the unique conformational state of each polymer molecule. This review aims to give an insight into the latest results of the application of single-molecule spectroscopy to the study of individual polymer chains. In particular, we focus on the relationship between the conformation (or structure) of the chain on the one hand and its physical properties on the other, primarily with respect to a very important class of organic semiconductors, the conjugated polymers. We review how the conformation of an individual polymer chain is reflected in its photophysical properties, such as exciton migration and localization, and fluorescence spectra. The review also covers the relationship between the conformation of synthetic non-conjugated polymers and their rheological properties.