Supramolecular Sequential Light-Harvesting Systems for Constructing White LED Device and Latent Fingerprint Imaging.

The fabrication of supramolecular light-harvesting systems (LHS) with sequential energy transfer is of significance in utilizing light energy. In this study, we report the non-covalent self-assembly of a sequential LHS by pillar[5]arene-based host-guest interaction in water and its applications in white light-emitting diode (LED) device and latent fingerprint imaging. The host-guest complex WP5 ⊃ ${ \supset }$ G self-assembles into nanoparticles in water and shows enhanced aggregation-induced emission (AIE) effect. The nanoparticles can be further used to construct sequential LHS with fluorescent dyes 4,7-di(2-thienyl)-benzo[2,1,3]thiadiazole (DBT) and sulforhodamine 101 (SR101). Impressively, the system shows white-light emission when the molar ratio of WP5 ⊃ ${ \supset }$ G/DBT/SR101 is 1100/2/16. The material can be coated on a LED bulb to achieve white-light emission. In addition, the sequential LHS exhibit multicolor fluorescence including red emission, which have been successfully applied to high-resolution imaging of latent fingerprints. Therefore, we demonstrated a general strategy for the construction of sequential LHS in water based on macrocyclic host-guest interaction and explored its multi-functional applications in white-light LED device and imaging of latent fingerprints, which will promote future development and application of supramolecular LHSs.

A sequential light-harvesting system with thermosensitive colorimetric emission in both aqueous solution and hydrogel.

Inspired by natural photosynthetic systems that feature both sequential energy transfer and temperature response, we herein report an artificial thermosensitive sequential light-harvesting system (LHS) based on an amphiphilic molecule TPEO. It self-assembles into fluorescent nanoparticles in water and shows tunable LCST behavior. By loading ESY as the first acceptor and NiR as the second acceptor into the nanoparticles, an artificial LHS with two-step FRET was successfully constructed. Interestingly, the system exhibits thermosensitive colorimetric fluorescence in both aqueous solution and hydrogel by taking advantage of a combination of LCST and sequential FRET.

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.

A diketopyrrolopyrrole-based small molecule with an extended conjugated skeleton and J-aggregation behavior for 808 nm laser triggered phototheranostics.

The development of phototheranostic agents, specifically those based on organic small molecules (OSMs) with long wavelength excitation/emission, is an attractive but challenging project. In this contribution, we designed and synthesized a novel conjugate small molecule with a linear structure, named DPP-OPIC. Water-soluble nanoparticle DPP-OPIC NPs were fabricated. They exhibited strong absorption in the region of 600-1000 nm, which was due to the extended conjugate length of the molecular skeleton and J-aggregation behavior. Under 808 nm laser excitation, DPP-OPIC NPs were capable of producing outstanding near-infrared-II (NIR-II, 900-1700 nm) fluorescence. The photoluminescence quantum yield was determined as 0.58%, which enabled high-resolution in vivo tumor imaging. Additionally, a notable photothermal effect with a high photothermal conversion efficiency (41.5%) was achieved by the irradiation of DPP-OPIC NPs. Hence, DPP-OPIC NPs can be used as superior phototheranostic agents, providing valuable contributions to NIR-II fluorescence imaging and photothermal therapy.

High-Performance Hybrid Phototheranostics for NIR-IIb Fluorescence Imaging and NIR-II-Excitable Photothermal Therapy.

Photothermal therapy operated in the second near-infrared (NIR-II, 1000-1700 nm) window and fluorescence imaging in the NIR-IIb (1500-1700 nm) region have become the most promising techniques in phototheranostics. Their combination enables simultaneous high-resolution optical imaging and deep-penetrating phototherapy, which is essential for high-performance phototheranostics. Herein, carboxyl-functionalized small organic photothermal molecules (Se-TC) and multi-layered NIR-IIb emissive rare-earth-doped nanoparticles (NaYF4:Yb,Er,Ce@NaYF4:Yb,Nd@NaYF4, RENP) were rationally designed and successfully synthesized. Then, high-performance hybrid phototheranostic nanoagents (Se-TC@RENP@F) were easily constructed through the coordination between Se-TC and RENP and followed by subsequent F127 encapsulation. The carboxyl groups of Se-TC can offer strong binding affinity towards rare-earth-doped nanoparticles, which help improving the stability of Se-TC@RENP@F. The multilayered structure of RENP largely enhance the NIR-IIb emission under 808 nm excitation. The obtained Se-TC@RENP@F exhibited high 1064 nm absorption (extinction coefficient: 24.7 L g-1 cm-1), large photothermal conversion efficiency (PCE, 36.9%), good NIR-IIb emission (peak: 1545 nm), as well as great photostability. Upon 1064 nm laser irradiation, high hyperthermia can be achieved to kill tumor cells efficiently. In addition, based on the excellent NIR-IIb emission of Se-TC@RENP@F, in vivo angiography and tumor detection can be realized. This work provides a distinguished paradigm for NIR-IIb-imaging-guided NIR-II photothermal therapy and establishes an artful strategy for high-performance phototheranostics.

Host-Guest Complexes of Pillar[5]arene as Components for Supramolecular Light-Harvesting Systems with Tunable Fluorescence.

A guest molecule containing a short alkyl spacer between the tetraphenylethylene group and the methylpyridinium group was designed and synthesized. After complexation with a water-soluble pillar[5]arene, the resulting host-guest complex can further self-assemble into fluorescence-emitting nanoparticles in water. By loading a commercially available dye Rhodamine 6G into the nanoparticles, an efficient artificial light-harvesting system with high donor/acceptor ratios (>400/1) was successfully constructed. The obtained systems show considerable antenna effects with values of more than 10 times. The system also exhibits tunable fluorescence emission behavior and can be used as a fluorescent ink for information encryption.

Photoactive oligomer with D-D'-A-D'-D''-D'-A-D'-D scaffold for high-efficiency NIR-II phototheranostics.

A D-D'-A-D'-D''-D'-A-D'-D type photoactive oligomer (O-BT) based nanoparticles (NPs) were prepared for biomedical application. The O-BT NPs possessed a high extinction coefficient, excellent hyperthermia generation ability, satisfactory NIR-II fluorescence emission, and good batch-to-batch reproducibility, and could be used as high-efficiency phototheranostics for photothermal therapy and NIR-II fluorescence imaging.

Fluorescent Nanoassemblies in Water Exhibiting Tunable LCST Behavior and Responsive Light Harvesting Ability.

Responsive fluorescent nanomaterials have been received considerable attention in recent years. In this work, a bola-type amphiphilic molecule, CSO, was synthesized which contains a hydrophobic cyanostilbene core and hydrophilic oligo(ethylene glycol) (OEG) coils at both sides. The cyanostilbene group is aggregation-induced emission (AIE) active, while the OEG coils are thermo-responsive. As a result, the CSO molecules can self-assemble into blue-fluorescent nanoassemblies with lower critical solution temperature (LCST) behavior in aqueous media. It is noteworthy that the LCST behavior can be reversibly regulated with changes in concentration and the introduction of K+ . Intriguingly, fluorescence of CSO assembly shows a blue-shift upon heating. Finally, by employing CSO as a light capturing antenna and energy donor, an artificial light harvesting system with tunable emission and thermo-responsive characteristics was fabricated. This study not only demonstrates an integrated approach to create responsive fluorescent nanomaterials, but also shows great potential for producing luminescent materials and mimicking photosynthesis in nature.

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-assembled Fluorescent Nanoparticles with Tunable LCST Behavior in Water.

The development of stimuli-responsive fluorescent materials in water based on organic molecule has drawn significant interest. Herein, we designed and synthesized an amphiphilic molecule M containing a fixed tetraphenylethylene moiety (FTPE) as hydrophobic part and tri(ethylene glycol) (TEG) chains as hydrophilic part. Notably, the FTPE moiety is aggregation-induced emission (AIE) active, while the TEG chains are thermo-responsive. M can self-assemble into fluorescent nanoparticles (NPs) in water, which showed lower critical solution temperature (LCST) behavior. Moreover, its clouding point can be reversibly tuned upon the concentration variation. Interestingly, the NPs can be acted as a fluorescence thermometer in aqueous media owing to their unique AIE and LCST behaviors. Our work herein not only provides an integration strategy to construct stimuli-responsive fluorescent materials but also shows great potential in biological applications including bioimaging and biosensors.

An ultralow-acceptor-content supramolecular light-harvesting system for white-light emission.

White-light emission in donor-acceptor systems usually requires relatively high acceptor content and/or multiple acceptors to "neutralize" the primary color of donors. Herein, a cyanostilbene-bridged ditopic ureidopyrimidinone donor (CSU) was designed and synthesized, which can self-assemble into dispersed nanoparticles in water. Fascinatingly, efficient white-light emission can be realized by co-assembling 0.1% DBT into the nanoparticles through a light-harvesting strategy. This new system is further demonstrated for use in white-light encryption materials.

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

The design and construction of an artificial light-harvesting system in water by mimicking the energy transfer cascade in natural photosynthesis are of significant importance. Herein, we report an efficient two-step sequential energy transfer system based on quadruple hydrogen-bonded supramolecular polymeric nanoparticles. By loading two types of hydrophobic dyes as energy acceptors, excitation energy from the supramolecular polymer could be funneled efficiently to the final acceptor through the relay acceptor. The system exhibits tunable multicolor emission from blue through yellow to red, as well as white light emission.

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 Polymers With AIE Property Fabricated From a Cyanostilbene Motif-Derived Ditopic Benzo-21-Crown-7 and a Ditopic Dialkylammonium Salt.

Fluorescent supramolecular polymers (FSP) have attracted considerable attention in recent years. Particularly, the incorporation of aggregation-induced emission (AIE) property to the FSP will bring this material into practical applications. Herein, we designed and synthesized a cyanostilbene motif derived ditopic benzo-21-crown-7 (B21C7) as a host molecule (H). The cyanostilbene motif endows H with AIE property while the B21C7 motif renders it with the capability to complex with electron deficient guest molecules. Upon the addition of a ditopic dialkylammonium salt molecule (G), a novel FSP with blue luminescent property can be constructed. This B21C7-based host-guest FSP with blue fluorescence may have potential application in supramolecular luminescent materials.

Reversible hydrogen-bonded polymerization regulated by allosteric metal templation.

Allosteric effects are common in biology, but have not been fully explored in the control of supramolecular polymerization. Herein, ditopic UPy derivatives with acyclic crown ether-like spacers were designed and synthesized, which can undergo supramolecular polymerization through quadruple hydrogen bonding. Upon the addition of K+, drastic molecular conformational change to the U-shape is induced by metal-coordination, reconfiguring remote UPy sites towards the formation of discrete cyclic dimers. Interestingly, the supramolecular polymerization can be restored by simply removing K+ by water-extraction.

An efficient artificial light-harvesting system with tunable emission in water constructed from a H-bonded AIE supramolecular polymer and Nile Red.

With the aid of CTAB amphiphile, water-phase artificial light-harvesting systems were fabricated as nanoparticles by the self-assembly of two low-molecular-weight organic molecules: a UPy-functionalized TPE derivative 1 with both supramolecular polymerization and AIE capabilities as a donor and a fluorescent chromophore NiR as an acceptor. Owing to the flexibility of supramolecular self-assembly, tunable emissions including white-light emission could be easily realized with high energy transfer efficiency and the antenna effect.

ß-D-Galactose-Functionalized Pillar[5]arene With Interesting Planar-Chirality for Constructing Chiral Nanoparticles.

Planar-chiral pillar[5]arenes bearing ß-D-galactose substituents on both rims have been successfully synthesized and effectively separated by silica gel chromatography with a high yield. The obtained (S p )- and (R p )-ß-D-galactose functionalized pillar[5]arenes [(S p-D )-GP5 and (R p-D )-GP5] exhibit the S p and R p planar chirality. Furthermore, (S p-D )-GP5 and (R p-D )-GP5 can not racemize according to dynamic 1H NMR and CD spectra. Notably, GP5 is able to capture a guest molecule (DNS-CPT) to form a host-guest supramolecular amphiphile, which can further self-assemble into chiral nanoparticles with the S p and R p planar chirality of (S p-D )-GP5 and (R p-D )-GP5 still being retained, suggesting GP5 could be as reliable chiral sources to transfer the S p and R p planar chirality.