Supramolecular cuboctahedra with aggregation-induced emission enhancement and external binding ability

A core-substituted naphthalene diimide-based supramolecular triangle and its self-assembly into nanostructures

A core-substituted naphthalene diimide (1) was self-assembled with (Et3P)2Pt·2TfO into a triangular structure (2) whereas an equilibrium mixture of triangular and dimer or tetramer was obtained with Pd(dppp)·2TfO and Pt(dppp)·2TfO. The triangular structure for 2 was supported theoretically by PM6 calculations and fully characterized by NMR spectroscopy and mass spectrometry. Complex 2, as compared to 1, shows a variable UV-Vis absorption and fluorescence as a function of solvent and is easily reducible during cyclic voltammetry. TEM and AFM imaging showed that 2 further self-assembles into nanostructures.

Supramolecular artificial light-harvesting systems incorporating aggregation-induced emissive components: from fabrication to efficient energy conversion

The harvesting and utilization of light energy have increasingly captivated researchers. The construction of artificial light harvesting systems (ALHSs) through supramolecular assemblies has emerged as a prominent approach. Following the discovery of the aggregation-induced emission (AIE) phenomenon, AIE luminogens (AIEgens) have been extensively employed to develop ALHSs, in which these molecules are assembled into nanoparticles or nanoaggregates to enhance energy transfer efficiency. In this review, we summarize recent research advances in supramolecular ALHSs based on AIEgens, including some representative examples reported by our research group and others. In particular, different design strategies for ALHSs formed by self-assembly of host-guest complexes and other building blocks such as macrocyclic and amphiphilic molecules have been discussed over the past three years. For host-guest complexes with AIE activity, we analyze the design principles of AIE-active hosts or guests, and how their self-assembly influences the efficiency of ALHSs. For AIE-active macrocycles or amphiphiles that do not form host-guest complexes, we discuss how they can independently self-assemble into ALHSs. Finally, future research directions for the utilization of AIEgens in the development of ALHSs are discussed.

A stimuli-responsive dimeric capsule built from an acridine-based metallacycle for ratiometric fluorescence sensing of TNP

Stimulus-responsive luminescent metal-organic architectures have received a lot of attentions in supramolecular chemistry. Herein, we report the synthesis of an acridine-based metal-organic macrocycle that undergoes reversible interconversion between the monomer and the dimer states in response to variations in the concentration and solvent, resulting in a switch between blue and green fluorescence. X-ray structure analysis reveals that hydrogen bonds between benzimidazole C-H and NO3- anions, along with π-π interactions between acridines, are the primary driving forces behind this behavior of the assembly. The stimuli-responsive supramolecular fluorescence switching originates from the monomer and excimer states. The addition of 2,4,6-trinitrophenol (TNP) leads to a fluorescence "turn-off" at 430 nm for the monomer and a "turn-on" at 520 nm for the dimer, thus facilitating the ratiometric detection of TNP with the detection limit being as low as 13 ppb. Our work provides valuable insights into the construction of stimuli-responsive materials for fluorescence sensing.

Self-assembly and dynamic exchange of cuboctahedral metal-organic cages

Due to their unique physical and chemical properties, metal-organic cage structures have great potential for applications in various fields. However, current studies have mainly focused on highly symmetric structures assembled from single metal ions and organic ligands, limiting their diversity and complexity, and there are still relatively few studies on the dynamic formation process of metal-organic cages. Herein, we constructed a series of metal-organic cages with different sizes assembled from the highly-stable coordination of 2,2':6',2''-terpyridine-based tetratopic ligands and various metals ions such as Zn, Cu, Co and Fe. Furthermore, the intermolecular exchange process between the metal-organic cages was explored through the dynamic exchange of ligands, and the formation of a series of hybrid supramolecular nanocages together with their final tendency to form a predominant structure of M24L14L28 was observed. In addition, the binding of metal-organic cages with 5,10,15,20-tetrakis(3,4,5-trimethoxyphenyl) porphyrin-Zn was also investigated. This study not only expands the complexity and diversity of metal-organic cages, but also provides a new perspective for studying the dynamic behaviour of metal-organic cages.

Aggregation-Induced Emission via the Restriction of the Intramolecular Vibration Mechanism of Pinacol Lanthanide Complexes

Pinacol lanthanide complexes PyraLn (Ln = Dy and Tb) with the restriction of intramolecular vibration were obtained for the first time via an in situ solvothermal coordination-catalyzed tandem reaction using cheap and simple starting materials, thereby avoiding complex, time-consuming, and expensive conventional organic synthesis strategies. A high-resolution electrospray ionization mass spectrometry (HRESI-MS) analysis confirmed the stability of PyraLn in an organic solution. The formation process of PyraLn was monitored in detail using time-dependent HRESI-MS, which allowed for proposing a mechanism for the formation of pinacol complexes via in situ tandem reactions under one-pot coordination-catalyzed conditions. The PyraLn complexes constructed using a pinacol ligand with a butterfly configuration exhibited distinct aggregation-induced emission (AIE) behavior, with the αAIE value as high as 60.42 according to the AIE titration curve. In addition, the PyraLn complexes in the aggregated state exhibit a rapid photoresponse to various 3d metal ions with low detection limits. These findings provide fast, facile, and high-yield access to dynamic, smart lanthanide complex emissions with bright emission and facilitate the rational construction of molecular machines for artificial intelligence.

Construction of 1,3,5-Triazine-Based Prisms and Their Enhanced Solid-State Emissions

In this study, two trigonal prisms based on the 1,3,5-triazine motif (SA and SB), distinguished by hydrophobic groups, were prepared by the self-assembly of tritopic terpyridine ligands and Zn(II) ions. SA and SB exhibited high luminescence efficiencies in the solid state, overcoming the fluorescence quenching of the 1,3,5-triazine group caused by π-π interactions. Notably, SA and SB exhibited different luminescence behaviors in the solution state and aggregation state. SB with 12 alkyl chains exhibited extremely weak fluorescence in a dilute solution, but its fluorescence intensity and photoluminescence quantum yield (PLQY) were significantly enhanced in the aggregated state (with the increase in the water fraction), especially in the solid state. Different from the gradually enhanced efficiency of SB, the PLQY of SA gradually decreased with the increase in aggregation but still maintained a high luminescence efficiency. These two complexes exhibited different modes to solve the fluorescence quenching of 1,3,5-triazine in the solid state. The hierarchical self-assembly of SB exhibited nanorods owing to the hydrophobic interactions of alky chains, while SA aggregated into spheres under the influence of π-π interactions.