General strategies leading to scale-span molecular self-assembly are of crucial importance in creating bulk supramolecular materials. Here, we report that under mechanical pressure, caking of the precipitated molecular self-assemblies led to bulk supramolecular films. Massive fabrication of supramolecular films became possible by employing a simple household noodle machine. The film could be endowed to acquire diversified functions by depositing various functional ingredients via coprecipitation. We expect that our current work opens up a new paradigm leading to large-scale functional solid molecular self-assembled materials.
Caking of powder materials is undesired in various industries, and for thousands of years people are fighting against caking. Herein, the principle of caking is employed to create macroscopic plastic supramolecular films through a cold sintering process. A nanometer-sized, irregular coordinating cluster is first generated with a bulky head surfactant and multifunctional ligand, and the addition of metal ions immediately leads to amorphous white precipitates. Upon adsorbing moisture, a rearrangement of the molecules in the precipitates results in cold sintering, so that the particles in the precipitates grow into a transparent macroscopic film. The mechanical strength of the film is comparable to plastics, but allows welding and molding with finger at ambient temperature in moist environment. Mechanical tests suggest the supramolecular plastic does not fatigue even after several tens circles' remolding, indicating their superior material engineering capability. This strategy can be extended to different chemistries to fabricate films with different mechanical strength. Various functional components can be doped into the resultant films, rendering them a platform toward multifunctional materials, such as luminescent devices or sensors for pollution gases. The current strategy opens up a new vista in material science is expected.
Cis-to-trans transition of azobenzene compounds usually occurs under appropriate light irradiation or slow thermal relaxation, and one can hardly obtain complete cis-to-trans transition of azos due to the overlap of the n-π* transition of the trans and the cis isomers. We show that by viewing the photostationary state as a chemical equilibrium between the cis and trans isomers, triggered self-assembly of the trans isomers can promote the cis-to-trans transition, and trans azos with spectrum-grade purity can even be achieved using an elegantly designed coordinating azo. This work establishes a new paradigm for manipulating the cis-to-trans transition of azo compounds, which may inspire designs for various azo-based advanced materials.
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