Manipulating Aggregation‐Induced Emission with Supramolecular Macrocycles

Abstract

host and guest bears excellent selectivity. [5] On the other hand, the noncovalent interactions are sensitive to various influential elements in the surrounding environment, including light irradiation, [6] redox reactions, [7] pH variations, [8] competitive factors, [9] and chemical or biological interfering. [10,11] Owing to the highly desired characteristics of host-guest systems comprising of supramolecular macrocycles and their guests, the dynamic nature of their molecular activities, the reversibility between assembly and disassembly, the particular intermolecular recognition and the responsiveness toward external stimuli, supramolecular host-guest systems become outstanding candidates as building blocks in the construction of nanoscaled smart materials with controllable properties, which are substantial in the research ranges of nanotechnology and materials science. Up till today, a number of host compounds, such as crown ethers, [12,13] cyclodextrins (CDs), [14] calixarenes, [15] cucurbit[n]urils (CB[n]s), [16][17][18] and pillararenes, [19,20] on account of their developed synthetic procedures, relatively high yieldings, numerous modification possibilities and tunability, [21,22] along with their well-explored host-guest properties, [5] have been utilized to construct stimuliresponsive smart materials to serve as either supramolecular recognizing agents or the major building blocks for reversible artificial complexes. [1,23,24] An important use of macrocyclic compounds to create functional smart materials lies in the construction of controllable fluorescent systems. [25] In the literature, one can find considerable examples of fluorescent systems manipulated by supramolecular macrocycles through their distinctive inclusion complexation activities. [26][27][28][29] The concept of aggregation-induced emission (AIE) was first proposed by Tang and co-workers in 2001, [30] demonstrating an unprecedented fluorescent phenomenon, which bears luminescent features in sharp contrast to the traditional aggregation-caused quenching (ACQ) that is typical for conventional organic fluorophores. While the ACQ effect stands as a major hindrance for the solidation of luminescent materials since luminophores with planar molecular structures undergo fluorescence quenching in aggregated state, dye molecules possessing unplanar conformations, on the contrary, are able to exhibit stronger emission upon aggregation according to the restriction of intramolecular motions (RIM) or rotations (RIR), which suppresses nonradiative relaxation and actuates the energy release through radiative pathway. [31,32] Two essential elements of smart materials are their capabilities of responding to external stimuli and the specific recognition toward different targets, which renders supramolecular macrocycles an ideal type of building blocks for materials construction. Aggregation-induced emission (AIE) has been intensively investigated for two decades not only for the realization of solid-state fluorescent materials, but also for the fabrication...

Multistimuli Response and Polymorphism of a Novel Tetraphenylethylene Derivative

“…Stimuli‐responsive materials are defined as the materials that show physical or chemical responses to external stimuli, such as pH, vapors, temperature, pressure, electricity, light, and so on . Fluorescence upon external stimuli is a most commonly used property that has the advantage of easy detection and low cost.…”

Organic-Inorganic Hybrid Pillarene-Based Nanomaterial for Label-Free Sensing and Catalysis

“…[32][33][34][35] Supramolecular chemistry based on macrocycles such as crown ethers, 36 cyclodextrins, 37 cucurbiturils, 38 calixarenes, 39 pillararenes, 40 and other synthetic macrocycles [41][42][43][44][45][46][47] has drawn tremendous attention in terms of the design, synthesis, and functionalization of macrocyclic compounds and their versatile potential applications, particularly in hybrid nanomaterials utilizing their recognition properties. [48][49][50][51] Pillar[n]arenes (pillarenes for short), a relatively new class of macrocyclic host first reported by Ogoshi et al in 2008, 52 continue to be of interest due to their symmetric pillar-shaped structures, adjustable cavity size, ease of chemical modification, and host-guest recognition capabilities. 53 A series of water-soluble pillar[n]arenes have been investigated to stabilize noble metal nanoparticles, endowing them with water…”

Enhanced Solution and Solid‐State Emission and Tunable White‐Light Emission Harvested by Supramolecular Approaches

“…The supramolecular assembly approach based on macrocycles has proven to be an efficient way to fabricate fluorescent materials with tunable wavelength, with the charge and energy transfer being facilitated by host–guest interactions . Noncovalent interactions in supramolecular assemblies endow these fluorescent materials with controllable, stimuli‐responsive, and reversible features .…”

“…AIEgens exhibit enhanced emission in their aggregated state, ascribed to the propeller‐like structures that avoid intermolecular π–π stacking and result in the restriction of intramolecular rotation (RIR) . Inspired by this significant breakthrough, many researchers over the past two decades have devoted their efforts to the design and fabrication of fluorescent materials with AIE properties . However, synthetic macrocycles such as pillarenes have rarely been used to boost the properties of emissive compounds to obtain persistent and enhanced emission in both solution and the solid state, including single crystals, as well as tunable white‐light emission, no matter whether through covalent linkages or noncovalent host–guest complexation.…”