Efficient artificial light-harvesting systems based on aggregation-induced emission in supramolecular gels

Construction of an Artificial Sequential Light-Harvesting System and White-Light Material Utilizing Supramolecular Gels

The molecular (pyren-1-yloxy)-acetic acid (Py) with excellent fluorescence properties was synthesized from 1-hydroxypyrene (Hp) and formed a supramolecular gel with an acid-base stimulus response in dimethylformamide and water. On the basis of gel, the fluorescent dye perylene 3, 9-dicarbxylic acid, and rhodamine 6g were added successively to construct a step-by-step artificial light-harvesting system, so that the fluorescence color changed from blue-purple to green to red, and white light emission was realized by adjusting the ratio of donors and acceptors.

Boosting Excited-State Energy Transfer by Anchoring Dipole Orientation in Binary Thermally Activated Delayed Fluorescence/J-Aggregate Assemblies

Förster resonance energy transfer (FRET) has been widely applied in fluorescence imaging, sensing and so on, while developing useful strategy of boosting FRET efficiency becomes a key issue that limits the application. Except optimizing spectral properties, promoting orientation factor (κ2) has been well discussed but rarely utilized for boosting FRET. Herein, we constructed binary nano-assembling of two thermally activated delayed fluorescence (TADF) emitters (2CzPN and DMAC-DPS) with J-type aggregate of cyanine dye (C8S4) as doping films by taking advantage of their electrostatic interactions. Time-resolved spectroscopic measurements indicated that 2CzPN/Cy-J films exhibit an order of magnitude higher kFRET than DMAC-DPS/Cy-J films. Further quantitative analysing on kFRET and kDET indicated higher orientation factor (κ2) in 2CzPN/Cy-J films play a key role for achieving fast kFRET, which was subsequently confirmed by anisotropic measurements. Corresponding DFT/TDDFT calculation revealed strong "two-point" electrostatic anchoring in 2CzPN/Cy-J films that is responsible for highly orientated transitions. We provide a new strategy for boosting FRET in nano-assemblies, which might be inspired for designing FRET-based devices of sensing, imaging and information encryption.

An anti-freeze fluorescent organogel with rapid shape-forming properties for constructing artificial light harvesting systems used in extremely cold environments

Using polyvinyl alcohol (PVA) and perylene-3,9-dicarboxylic acid (PDA) as raw materials, a new anti-freeze (-50 °C) fluorescent organogel with rapid shape-forming (2 h) properties was synthesised based on a certain proportion of the binary solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). Then, an artificial light-harvesting system (ALHS) used in extremely cold environments was successfully constructed by mixing fluorescent dyes sulphorhodamine101 (SR101) and rhodamine 6G (R6G) into them as acceptors.

Self-assembled supramolecular artificial light-harvesting nanosystems: construction, modulation, and applications

Artificial light-harvesting systems, an elegant way to capture, transfer and utilize solar energy, have attracted great attention in recent years. As the primary step of natural photosynthesis, the principle of light-harvesting systems has been intensively investigated, which is further employed for artificial construction of such systems. Supramolecular self-assembly is one of the feasible methods for building artificial light-harvesting systems, which also offers an advantageous pathway for improving light-harvesting efficiency. Many artificial light-harvesting systems based on supramolecular self-assembly have been successfully constructed at the nanoscale with extremely high donor/acceptor ratios, energy transfer efficiency and the antenna effect, which manifests that self-assembled supramolecular nanosystems are indeed a viable way for constructing efficient light-harvesting systems. Non-covalent interactions of supramolecular self-assembly provide diverse approaches to improve the efficiency of artificial light-harvesting systems. In this review, we summarize the recent advances in artificial light-harvesting systems based on self-assembled supramolecular nanosystems. The construction, modulation, and applications of self-assembled supramolecular light-harvesting systems are presented, and the corresponding mechanisms, research prospects and challenges are also briefly highlighted and discussed.

Construction of Artificial Light-Harvesting Systems Based on Aggregation-Induced Emission Type Supramolecular Self-Assembly Metallogels

A method for preparing new artificial light-harvesting systems (ALHSs) based on supramolecular metallogels was proposed. Various metal ions were introduced into a solution of a bi-benzimidazole compound (P) in ethylene glycol, and P exhibited high selectivity toward Al3+, as indicated by the noticeable red shift (49 nm) observed in the fluorescence spectra of P after the addition of Al3+. Interestingly, the gelator, P, could self-assemble into a stable supramolecular gel (P-gel) that exhibits strong aggregation-induced emission in ethylene glycol. Thus, two ALHSs were successfully prepared in a gel environment. The P-Al3+ assembly acts as the donor in the ALHSs, while BODIPY 505/515 (BDP) and rhodamine 6G (Rh6G), which are loaded onto the P-Al3+ assembly, act as acceptors. In these two diverse systems, the occurrence of an energy transfer process is confirmed from the P-Al3+ assembly to BDP and Rh6G. The findings of this study will enable the design and fabrication of ALHSs.

Artificial light-harvesting systems based on supramolecular self-assembly multi-component metallogels

This paper proposes a strategy for fabricating new artificial light-harvesting systems (ALHSs) based on supramolecular multi-component metallogels. Al³⁺ was introduced into a solution of an acylhydrazone compound (L) in DMSO or DMF to form the L-Al³⁺ assembly. After adding Al³⁺ to the L solution, a noticeable blue shift appeared in the fluorescence spectra of L. Moreover, L could form a gel (L-B-gel) with 1,3:2,4-dibenzylidene sorbitol (B) in a DMSO-H₂O binary solution. Finally, we obtained a multi-component metallogel (L-Al³⁺-B-gel) and successfully fabricated two ALHSs (L-Al³⁺/rhodamine 6G (Rh6G) and L-Al³⁺/rhodamine B (RhB)). In these systems, the L-Al³⁺ supramolecular assembly acts as the donor, while Rh6G and RhB act as acceptors. Additionally, we confirmed an energy-transfer process from the L-Al³⁺ component to Rh6G and RhB separately. The proposed fabrication strategy will facilitate the development of ALHSs.

Supramolecular Polymer Gel Lubricant with Excellent Mechanical Stability and Tribological Performances

Lubricants performing better in machinery systems would lead to the remarkable reduction of environmental pollution problems and the significant improvement of fuel economy. A new family of supramolecular polymer gel lubricants with urea groups has been successfully prepared via self-assembling noncovalent bonds. These newly designed supramolecular polymer gels were well characterized with field-emission scanning electron microscopy, proton nuclear magnetic resonance, attenuated total reflection-Fourier transform infrared spectroscopy, a rheometer, oscillating reciprocating friction, and a wear tester. Compared to low molecular weight supramolecular gels, the covalent and noncovalent bonds cooperated in the supramolecular polymer gel based on macromolecules. Hence, the mechanical properties and viscoelasticity of gel lubricants are greater than those of the low molecular weight supramolecular gels. Furthermore, owing to the longer chain length of polymer gelators, the thickness of the adsorbed film formed on the surface lubricated by macromolecules is thicker than that on the surface lubricated by low molecular weight supramolecular gels, which positively correlates with the lubricating property, making supramolecular polymer gels based on macromolecules better than low molecular weight supramolecular gels. Excitingly, the supramolecular polymer gels based on macromolecules exhibit more excellent thermal reversibility, creep recovery, and thixotropic properties, which not only achieve the lubricating property but also lead to the remarkable reduction of environmental pollution problems due to oil creeping.

Acridine Based N-Acylhydrazone Derivatives as Potential Anticancer Agents: Synthesis, Characterization and ctDNA/HSA Spectroscopic Binding Properties

A series of novel acridine N-acylhydrazone derivatives have been synthesized as potential topoisomerase I/II inhibitors, and their binding (calf thymus DNA—ctDNA and human serum albumin—HSA) and biological activities as potential anticancer agents on proliferation of A549 and CCD-18Co have been evaluated. The acridine-DNA complex 3b (-F) displayed the highest Kb value (Kb = 3.18 × 103 M−1). The HSA-derivatives interactions were studied by fluorescence quenching spectra. This method was used for the calculation of characteristic binding parameters. In the presence of warfarin, the binding constant values were found to decrease (KSV = 2.26 M−1, Kb = 2.54 M−1), suggesting that derivative 3a could bind to HSA at Sudlow site I. The effect of tested derivatives on metabolic activity of A549 cells evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide or MTT assay decreased as follows 3b(-F) > 3a(-H) > 3c(-Cl) > 3d(-Br). The derivatives 3c and 3d in vitro act as potential dual inhibitors of hTopo I and II with a partial effect on the metabolic activity of cancer cells A594. The acridine-benzohydrazides 3a and 3c reduced the clonogenic ability of A549 cells by 72% or 74%, respectively. The general results of the study suggest that the novel compounds show potential for future development as anticancer agents.

Novel fluorescent self-assembling material with gel properties: ion recognition and energy transfer

A novel fabrication strategy for preparing fluorescent nanomaterials has been proposed based on supramolecular self-assembly complexes and energy transfer. Here a dual acylhydrazone-functionalized molecule (DAF) was designed and synthesized by...

Chromophoric Dendrimer-Based Materials: An Overview of Holistic-Integrated Molecular Systems for Fluorescence Resonance Energy Transfer (FRET) Phenomenon

Dendrimers (from the Greek dendros → tree; meros → part) are macromolecules with well-defined three-dimensional and tree-like structures. Remarkably, this hyperbranched architecture is one of the most ubiquitous, prolific, and recognizable natural patterns observed in nature. The rational design and the synthesis of highly functionalized architectures have been motivated by the need to mimic synthetic and natural-light-induced energy processes. Dendrimers offer an attractive material scaffold to generate innovative, technological, and functional materials because they provide a high amount of peripherally functional groups and void nanoreservoirs. Therefore, dendrimers emerge as excellent candidates since they can play a highly relevant role as unimolecular reactors at the nanoscale, acting as versatile and sophisticated entities. In particular, they can play a key role in the properties of light-energy harvesting and non-radiative energy transfer, allowing them to function as a whole unit. Remarkably, it is possible to promote the occurrence of the FRET phenomenon to concentrate the absorbed energy in photoactive centers. Finally, we think an in-depth understanding of this mechanism allows for diverse and prolific technological applications, such as imaging, biomedical therapy, and the conversion and storage of light energy, among others.