Multi-step FRET systems based on discrete supramolecular assemblies

Fluorescence resonance energy transfer (FRET) from the excited state of the donor to the ground state of the acceptor is one of the most important fluorescence mechanisms and has wide applications in light-harvesting systems, light-mediated therapy, bioimaging, optoelectronic devices, and information security fields. The phenomenon of sequential energy transfer in natural photosynthetic systems provides great inspiration for scientists to make full use of light energy. In recent years, discrete supramolecular assemblies (DSAs) have been successively constructed to incorporate donor and multiple acceptors, and to achieve multi-step FRET between them. This perspective describes recent advances in the fabrication and application of DSAs with multi-step FRET. These DSAs are categorized based on the non-covalent scaffolds, such as amphiphilic nanoparticles, host-guest assemblies, metal-coordination scaffolds, and biomolecular scaffolds. This perspective will also outline opportunities and future challenges in this research area.

Non-Covalent Dimer as Donor Chromophore for Constructing Artificial Light-Harvesting System in Water

Dynamic emissive materials in aqueous media have received much attention owing to their ease of preparation, tunable luminescence and environmental friendliness. However, hydrophobic fluorophores usually suffer from aggregation-caused quenching in water. In this work, we constructed an artificial light-harvesting system by using a non-covalent aggregation-induced emission dimer as antenna and energy donor. The dimer is quadruple hydrogen bonded from a ureidopyrimidinone derivative (M) containing a tetraphenylethylene group. The dispersed nano-assemblies based on the dimer in aqueous media were fabricated with the help of surfactant. By loading a hydrophobic acceptor molecule DBT into the nano-assemblies, man-made light-harvesting nanoparticles were fabricated, showing considerable energy transfer efficiency and a relatively high antenna effect. Additionally, the fluorescence color of the system can be gradually tuned by varying the content of the acceptors. This study provides a general way for the construction of an aqueous light-harvesting system based on a supramolecular dimer, which is important for potential application in luminescent materials.

Self-Assembly of [3]Catenane and [4]Catenane Based on Neutral Organometallic Scaffolds

Transition metal-mediated templating and self-assembly have shown great potential to construct mechanically interlocked molecules. Herein, we describe the formation of the bimetallic [3]catenane and [4]catenane based on neutral organometallic scaffolds via the orthogonality of platinum-to-oxygen coordination-driven self-assembly and copper(I) template-directed strategy of a [2]pseudorotaxane. The structures of these bimetallic [3]catenane and [4]catenane were characterized by multinuclear NMR {¹H and ³¹P} spectroscopy, electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), and PM6 semiempirical molecular orbital theoretical calculations. In addition, single-crystal X-ray analyses of the [3]catenane revealed two asymmetric [2]pseudorotaxane units inside the metallacycle. It was discovered that tubular structures were formed through the stacking of individual [3]catenane molecules driven by the strong π-π interactions.

Efficient artificial light-harvesting system constructed from supramolecular polymers with AIE property

Supramolecular luminescent materials in water have attracted much interest due to their excellent tunability, multi-color emission, and environment-friendly behavior. However, hydrophobic chromophores are often affected by poor solubility and aggregation-caused quenching effects in aqueous media. Herein, we report a water-phase artificial light-harvesting system based on an AIE-type supramolecular polymer. Specifically, dispersed nanoparticles in water were prepared from an AIE chromophore-bridged ditopic ureidopyrimidinone (M) based supramolecular polymer with the assistance of surfactants. By co-assembling the hydrophobic chromophores NDI as energy acceptor into the nanocarriers, artificial light-harvesting systems (M-NDI) could be successfully constructed, exhibiting efficient energy transfer and high antenna effects. Furthermore, the spectral emission of the system could be continuously tuned with a relatively small number of acceptors. This work develops an efficient supramolecular light-harvesting system in water, which has potential applications in dynamic luminescent materials.

Supramolecular polymer-directed light-harvesting system based on a stepwise energy transfer cascade

An artificial light-harvesting system based on supramolecular polymeric nanoparticles has been successfully assembled in water, which displays efficient two-step sequential energy-transfer processes with a high antenna effect.