Reversible formation of soft coordination polymers from liquid mixtures of photoreactive organometallic ionic liquid and bridging molecules

Abstract

The reversible switching of bonding modes in coordination polymers through the application of external stimuli leads to versatile mechanical and electronic functions. However, the exploration of such a system remains a great challenge. In this study, we designed liquid mixtures comprising a photoreactive organometallic ionic liquid and a bridging ligand, which form intermolecular coordination bonds upon photoirradiation. The liquid mixture of an ionic liquid [Ru(C₅H₅){Ph(CH₂)₃CN}][(SO₂F)₂N] (1) and a tridentate ligand N(C₂H₄CN)₃ was transformed into an elastomer of an amorphous coordination polymer upon ultraviolet photoirradiation. By contrast, the photoirradiation of the mixture of 1 and a bidentate ligand NC(CH₂)₄CN produced a highly viscous liquid comprising coordination-bonded oligomers. In these reactions, photoirradiation causes dissociation of the organometallic cation, followed by the formation of intermolecular coordination bonds via the bridging ligands. The photoproducts underwent reverse reactions thermally. Based on coordination transformation, the ionic conductivity and viscoelasticity of these materials were reversibly controlled by the application of light and heat.