We review the synthesis, properties and applications of spin crossover polymer composites, polymers and some related 'soft' materials. These materials have received recently much attention because they provide an efficient way for the processing of spin crossover complexes in various shapes at various size scales and can give rise also to unique physical properties. First, we discuss in detail the state of the art of the elaboration of spin crossover polymer composites, using either inorganic complex precursors in solution or pre-formed spin crossover powder. A particular attention is paid on the influence of the polymer matrix on the spin crossover properties and on the use of 'active' polymers for development of synergies between the properties of the matrix and the load. Polymer composite devices for applications in the fields of artificial muscles, energy harvesting and thermochromic sensors are also highlighted. Then, more recent works, in which organic polymeric chains are used as ligands for the transition metal ions are presented. Finally, we overview various related 'soft' spin crossover compounds including spin crossover dendrimers, gels, liquid crystals and Langmuir Blodgett films with particular emphasis on compounds with supramolecular interactions of alkyl chains.
Bilayer spin-crossover nanocomposites show robust and controllable actuation cycles upon an electrical stimulus. The anisotropic shape of the particle and the mechanical coupling with the matrix can intensify the work output of the actuators.
[RuII(FT)(bipy)(NO)][PF6]3 [FT is the electron‐rich 4′‐(2‐fluorenyl)‐2,2′:6′,2′′‐terpyridine ligand and bipy is 2,2′‐bipyridine] is synthesized and characterized. It crystallizes in the triclinic P1 space group [a = 9.5362(2) Å, b = 10.3946(4) Å, c = 22.5701(8) Å, α = 94.7400(10)°, β = 94.9400(10)°, γ = 101.0680(10)]. A photochemical study is presented in comparison with that of the parents cis(Cl,Cl)‐[RuII(FT)Cl2(NO)][PF6] and trans(Cl,Cl)‐[RuII(FT)Cl2(NO)][PF6]. The three derivatives release nitric oxide (·NO) under irradiation at λ = 405 nm with respective quantum yields of 0.06, 0.31, and 0.10. Their two‐photon absorption (TPA) cross‐sections (σTPA) were investigated by the Z‐scan technique on related derivatives in which two hexyl chains were introduced to improve their solubility while their spectroscopic properties remained almost unaffected. The resulting σTPA values of 100 GM at λ = 800 nm are in the window of transparency for human tissues, and the bipyridine‐based complex exhibits a slight tendency for higher efficiency. The replacement of the [RuII(Cl)2(NO)] core by [RuII(bipy)(NO)] provides a much simpler synthesis, and the TPA‐induced ·NO‐release capabilities are in the same range of magnitude. Therefore, it is envisioned that ·NO donors of greater complexity with several metal centers could be investigated in future.
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