Intra- and intermolecular-interaction-controlled reversible core–shell structures and photoluminescent properties of lanthanide ion-doped diblock copolymers

Abstract

Lanthanide-based nanotechniques continue to attract considerable attention due to their current range of applications and broad potential in optical devices and biomedicine. Lanthanide ion-loaded block copolymers (BCPs) have gained interest, with questions remaining regarding their luminescence properties and structures. Solutions and films containing polystyrene-block-poly(2-vinylpyridine) (S2VP) and polystyrene-block-poly(4-vinylpyridine) (S4VP) loaded with trivalent lanthanide ions (Ln³⁺ = Eu³⁺, Tb³⁺) were prepared using a solvent displacement method and spin coating approach. Atomic force microscopy and transmission electron microscopy observations confirmed the Ln³⁺ distribution in the core of S2VP [Ln(x)] micelles and the corona of S4VP[Ln(x)] micelles. The coordination of Ln³⁺ and the S2VP core segment led to micelle shrinkage and film dewetting with increasing Ln³⁺ concentration, while the coordination of Ln³⁺ and the S4VP corona chain swelled the micelle. Photoluminescence investigations of the complex solutions showed typical reddish (Eu³⁺) and greenish (Tb³⁺) luminescence, and the emission intensity was enhanced with increasing Ln³⁺ concentration without typical fluorescence concentration quenching behavior. The luminescence intensity was distinctly enhanced when Ln³⁺ was distributed in the micellar core. Moreover, the emission spectra of mixed Eu–Tb ions complexes gave addition spectra of the two separated complexes. An orange color emission was observed because Eu³⁺ was more emissive. These results would improve understanding of ion coordination and lay the foundation for lanthanide ion/BCPs complex applications.