Real-time observation of conformational switching in single conjugated polymer chains

Fig. 2 Monitoring single P3HT chains in organic solvents. (A) Diagram of the sample chamber designed for single-molecule imaging in organic solvents including details of the injection system and the epifluorescence excitation and emission detection pathways. Components are not drawn to scale. (B) Schematic of the surface-anchoring strategy to covalently anchor single-P3HT chains to the glass substrate. (C) Representative single-molecule images of triethoxysilane-modified P3HT (left) and unmodified P3HT (right). (D) Box-plot comparison of the density of fluorescent spots observed using TES-P3HT (black) and unmodified P3HT (red). The extremes, upper and lower quartiles of the distribution, and the median are represented by the whiskers, box and middle lines, respectively. The whisker and upper quartile relative to sample P3HT are at the same value as the median. A 20-fold higher density of spots obtained for TES-P3HT compared to P3HT confirms specific covalent attachment of single chains via the silane end group. FOV, field of view.


Conjugated polymers (CPs) are an important class of organic semiconductors that combine novel optoelectronic properties with simple processing from organic solvents. It is important to study CP conformation in solution to understand the physics of these materials and because it affects the properties of solution-processed films. Single-molecule techniques are unique in their ability to extract information on a chain-to-chain basis; however, in the context of CPs, technical challenges have limited their general application to host matrices or semiliquid environments that constrain the conformational dynamics of the polymer. We introduce a conceptually different methodology that enables measurements in organic solvents using the single-end anchoring of polymer chains to avoid diffusion while preserving polymer flexibility. We explore the effect of organic solvents and show that, in addition to chain-to-chain conformational heterogeneity, collapsed and extended polymer segments can coexist within the same chain. The technique enables real-time solvent-exchange measurements, which show that anchored CP chains respond to sudden changes in solvent conditions on a subsecond time scale. Our results give an unprecedented glimpse into the mechanism of solvent-induced reorganization of CPs and can be expected to lead to a new range of techniques to investigate and conformationally manipulate CPs.

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