How to Solve a Common Problem of Organic Luminescent Materials: Concentration Quenching of Luminescence

Abstract

Concentration quenching is a common problem in organic luminescent materials, significantly reducing the efficiency of luminescent devices and luminescence-based tools. Although the mechanism of this phenomenon has been studied for a long time, it remains still not fully understood. It is a great challenge to find the most efficient ways to diminish or to overcome concentration quenching. This mini-review examines the progress made in biological and optoelectronic research to address this problem, mainly over the last decade. All known mechanisms of concentration quenching (except for light reabsorption and energy migration) are based on intermolecular interactions. Thus, to prevent or diminish concentration quenching of luminescence in organic molecules, one can only remove or reduce short-range interactions between the emitting molecules. Internal (adjusting the mutual orientation of the emitting molecules, designing molecules with bulky side chains, and sterically wrapping additional molecular parts, which results in increasing the distance between molecules) and external (host-guest systems, which isolate emitting molecules by means of creating a shielding barrier between them) tools for minimizing concentration quenching are considered. Shielding barriers can be obtained by doping and encapsulating molecules. Organic, metal-organic, and inorganic cages, organic, metal-organic, and inorganic frameworks, polymeric and inorganic nanoporous materials, as well as carbon and other nanomaterials, are being successfully developed for dye encapsulation. All the proposed tools have resulted in diminishing concentration quenching. However, for further progress in overcoming of concentration quenching, a series of new proposed approaches such as the synthesis of new sterically wrapped and Aggregation-Induced Emission (AIE) molecules, hyperfluorescent structures, and the embedding of luminescent molecules into organic, metal-organic, inorganic, and carbon-based cages as well as covalent organic and metal-organic frameworks are considered to be the most prospective, because they make it possible to apply the highest concentrations without essential luminescence quenching.