Nanomachines require molecular actuators to be coupled to a condensed phase. In this work, a redox responsive 1D contractible coordination polymer (ZnL) used as non-interlocked actuator is grafted onto superparamagnetic iron oxide nanoparticles (SPIONs) in a brush-like configuration. Oxidized rod-like ZnL oligomers have ability to reversibly self-fold upon reduction via π-dimerization of their bis-viologen units. Unlike in usual responsive brushes, ZnL chains behave individually, generating spatially controlled mechanical motion at nanoparticle surface associated to significant variations of particle diameters. ZnL oligomers were “grafted to” SPIONs in a single step. Reduction of colloidal dispersions was perform by visible light illumination with the help of a photoreductant. π-dimerization was assessed by UV–vis–NIR and reversible contraction of ZnL brush was characterized by DLS. Effects of ZnL chains length and grafting density on mechanism and performance of contractibility were studied. ZnL brush can alternately be contracted and extended with excellent reversibility. Combined UV–vis–NIR, DLS and TGA analyses demonstrate that π-dimerization is only intramolecular and that chains behave as independent actuators. Maximal contraction of 22 nm is obtained for largest particles ( D H = 86 nm). Full to partial contraction of the brush depends on grafting density with a threshold at ≈ 47 chains per particle.
Stimulus-responsive nanowires are attractive and expected to be used in diversified fields, but their application is usually affected by an inefficient synthetic process, impure morphologies, and unsteadiness in organic solvents. Meanwhile, the reversibility of the response is also challenging. Here, we present a new method incorporating polymerization-induced hierarchical self-assembly (PIHSA) and photodimerization to prepare cross-linked triblock copolymer nanowires, which were synthesized by the successive polymerization of methacrylate monomers containing azobenzene (MAAz) and stilbene (MAStb). The formation of nanowires was related to the highly ordered stacking of stilbene, and their heterostructures could be clearly identified by the distinct regions comprising azobenzene and stilbene at the periphery and center of the cores, respectively. Upon UV irradiation, the dimerization of stilbene cross-linked the structure and made the nanowires tolerant to good solvents. The cross-linked nanowires with appropriate block ratios were photoresponsive, which could reversibly expand and slim upon alternative UV/visible light irradiation due to the well-defined distribution of azobenzene and stilbene. This work will open a new door for the development and application of stimulus-responsive nanowires owing to their fascinating reversible deformation and distinguished stability.
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