Abstract
Dissipative self-assembly, which requires a continuous supply of fuel to maintain the assembled states far from equilibrium, is the foundation of biological systems. Among a variety of fuels, light, the original fuel of natural dissipative self-assembly, is fundamentally important but remains a challenge to introduce into artificial dissipative self-assemblies. Here, we report an artificial dissipative self-assembly system that is constructed from light-induced amphiphiles. Such dissipative supramolecular assembly is easily performed using protonated sulfonato-merocyanine and chitosan based molecular and macromolecular components in water. Light irradiation induces the assembly of supramolecular nanoparticles, which spontaneously disassemble in the dark due to thermal back relaxation of the molecular switch. Owing to the presence of light-induced amphiphiles and the thermal dissociation mechanism, the lifetimes of these transient supramolecular nanoparticles are highly sensitive to temperature and light power and range from several minutes to hours. By incorporating various fluorophores into transient supramolecular nanoparticles, the processes of aggregation-induced emission and aggregation-caused quenching, along with periodic variations in fluorescent color over time, have been demonstrated. Transient supramolecular assemblies, which act as fluorescence modulators, can also function in human hepatocellular cancer cells.
Highlights
Dissipative self-assembly, which requires a continuous supply of fuel to maintain the assembled states far from equilibrium, is the foundation of biological systems
SMEH can be transformed into anionic spiropyran (ASP), an anionic amphiphile, upon 420 nm irradiation, and the resulting ASP acts as an active building block for the dissipative self-assembly system
After keeping the abovementioned ASP solution in the dark at 25 °C, the absorbance at 424 nm gradually recovered to that of the original SMEH. According to these absorbance data as well as data reported in the literature[21], the conversion efficiency was calculated to be 95.1% (Supplementary Figs. 1 and 2), indicating an almost completely reversible conversion between the precursor SMEH and the active amphiphile ASP in aqueous solution at room temperature
Summary
Dissipative self-assembly, which requires a continuous supply of fuel to maintain the assembled states far from equilibrium, is the foundation of biological systems. Most artificial assemblies are constructed in a thermodynamic equilibrium state, while natural self-assemblies usually require a continuous energy supply to maintain an active and far-from-equilibrium assembled state with advanced functions Such an assembled state is referred to as dissipative selfassembly[3,4]. One method is to employ photoresponsive fluorophores as building blocks, which can lead to fluorescence variation upon light irradiation[17] Another method is to take advantage of the Förster resonance energy transfer process[18,19,20]. The transient supramolecular nanoparticles spontaneously disassemble in the dark (Fig. 1a) owing to the relaxation of ASP to SMEH This dissipative self-assembly system involves chemicals that are commercially available on a multigram scale and can operate in water at room temperature. An application of ASP-CS transient supramolecular nanoparticles in the staining of human hepatocellular cancer (HepG2) cells was demonstrated for dynamic cell imaging by modulating the loading of fluorophores[33,34]
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