Cyclodextrin‐Threaded Conjugated Polyrotaxanes for Organic Electronics: The Influence of the Counter Cations

A systematic investigation is reported into the influence of the counter cations on the optical, electrical and electroluminescent properties of polyelectrolytic conjugated polymers and of their cyclodextrin‐threaded rotaxanes. We compare conjugated polyelectrolytes with sulfonated side groups where the anionic charge is balanced by Li⁺, K⁺, Cs⁺, tetramethylammonium (Me₄N⁺) and cryptate‐encapsulated potassium (K⁺@2.2.2]). Narrowing (for the unthreaded analogues) and a slight red‐shift of the absorption spectra (for the rotaxanes) are found upon exchange of Li⁺ for larger cations, together with a blue‐shift and an efficiency enhancement of the luminescence. These effects are similar in nature to those induced by rotaxination, and are therefore assigned to a marked reduction of intermolecular interactions between the conjugated cores. Exchange of Li⁺ for K⁺, Cs⁺, or Me₄N⁺ results in a higher electroluminescence external quantum efficiency (EQE) for both polyrotaxanes and unthreaded polymers. For polyrotaxane‐based devices the EQE increased approximately 7 times upon substitution of Li⁺ with Cs⁺ or Me₄N⁺, thereby demonstrating the importance of the selection of the counter‐cations for optimizing the performance of polyelectrolytic conjugated polymers in light‐emitting devices.