Self‐Assembly of Aggregation‐Induced‐Emission Molecules

Abstract

The last decade has witnessed rapid developments in aggregation‐induced emission (AIE). In contrast to traditional aggregation, which causes luminescence quenching (ACQ), AIE is a reverse phenomenon that allows robust luminescence to be retained in aggregated and solid states. This makes it possible to fabricate various highly efficient luminescent materials, which opens new paradigms in a number of fields, such as imaging, sensing, medical therapy, light harvesting, light‐emitting devices, and organic electronic devices. Of the various important features of AIE molecules, their self‐assembly behavior is very attractive because the formation of a well‐defined emissive nanostructure may lead to advanced applications in diverse fields. However, due to the nonplanar topology of AIEgens, it is not easy for them to self‐assemble into well‐defined structures. To date, some strategies have been proposed to achieve the self‐assembly of AIEgens. Herein, we summarize the most recent approaches for the self‐assembly of AIE molecules. These approaches can be sorted into two classes: 1) covalent molecular design and 2) noncovalent supramolecular interactions. We hope this will inspire more excellent work in the field of AIE.

Understanding the Driving Mechanisms of Enhanced Luminescence Emission of Oligo(styryl)benzenes and Tri(styryl)‐s‐triazine

“…Fluorescence spectroscopy is one of the most used techniques to study molecular self‐assembly because fluorescence is very sensitive to changes in the molecular microenvironment, to restrictions of intramolecular motions, and to the electronic coupling between molecules . Sometimes, the aim goes beyond investigating the type of aggregate and the target is control of the molecular self‐assembly to improve the emissive properties of the material . This is not a trivial issue because molecular aggregation generally leads to quenching of the luminescence emission (aggregation‐caused quenching (ACQ)).…”

“…This is not a trivial issue because molecular aggregation generally leads to quenching of the luminescence emission (aggregation‐caused quenching (ACQ)). Fortunately, some compounds show enhanced luminescence upon aggregation (aggregation‐induced enhanced emission (AIEE)), which increases their possible applications . Different perspectives are used to explain this phenomenon: from conventional H or J aggregates, originating from Coulombic coupling in the framework of the theory of molecular excitons, to the short‐range excitonic coupling mechanism, due to wavefunction overlap between adjacent molecules .…”

“…[1,2] Consequently,c ontrol of the molecular self-assembly (dynamic or static)i sc urrently ah ot topic in different scientific disciplines, such as biology,c hemistry, and materials science. [1][2][3][4][5][6][7][8][9][10][11][12] In-trinsicc haracteristics of molecules, such as size, shape, and noncovalent forces, added to external factors, such as concentration, environmental polarity,v iscosity,o rt emperature, govern the molecular arrangemento fa ggregates in the liquid phase. [2][3][4][5][6] In the solid state, these factors, linked to bulk material processing,d etermine the competition of multiplea ggregation pathways for molecularb uilding blocks (pathway complexity).…”

“…[24] Sometimes, the aim goes beyondi nvestigating the type of aggregate and the targeti sc ontrol of the molecular self-assembly to improve the emissive properties of the material. [7,8,[25][26][27][28][29][30][31] This is not at rivial issue because molecular aggregation generally leads to quenching of the luminescence emission (aggregation-caused quenching (ACQ)). Fortunately,s ome compounds show enhanced luminescence upon aggregation( aggregation-induced enhanced emission (AIEE)), which increases their possible applications.…”

“…Fortunately,s ome compounds show enhanced luminescence upon aggregation( aggregation-induced enhanced emission (AIEE)), which increases their possible applications. [7,8,[25][26][27][28] Different perspectives are used to explain this phenomenon:f rom conventional Ho rJa ggregates, originating from Coulombic coupling in the framework of the theory of molecular excitons, [32][33][34] to the short-range excitonic coupling mechanism, due to wavefunction overlap between adjacent molecules. [35,36] On the other hand, the blockingo fn onradiative relaxation by restriction of intramolecular vibrations (RIVs), [25,26] as well as restricted access to conical intersections (RACIs) between excited and ground states and the blocking of Z/E photoisomerizations are other mechanisms commonly used to interpret AIEE phenomena.…”