From an excellent Review Article, published 12 April 2021,
“Circularly Polarized Luminescence from Organic Micro/nano-Structures.”
https://www.nature.com/articles/s41377-021-00516-7
From the Abstract:
“Circularly polarized light exhibits promising applications in future displays and photonic technologies. Circularly polarized luminescence (CPL) from chiral luminophores is an ideal approach to directly generating circularly polarized light, in which the energy loss induced by the circularly polarized filters can be reduced. Among various chiral luminophores, organic micro-/nano-structures have attracted increasing attention owing to the high quantum efficiency and luminescence dissymmetry factor. Herein, the recent progress of CPL from organic micro-/nano-structures is summarized.”
From the Introduction:
“This review focuses on the latest progress of organic micro-/nano-structures with CPL activity, aiming to provide a comprehensive insight into the relationship among molecular designs, assembly structures, and chiroptical properties. Firstly, we highlight the design principles of various micro-/nano-structures and the approaches for regulating CPL signals. Then, we introduce the applications of CPL-active materials in organic light-emitting diodes (OLEDs), optical information processing, and chemical and biological sensing. Finally, we will present the challenges and perspectives in this emerging field.”
“Unlike inorganic materials, organic materials are soft and flexible. Therefore, the hard top-down strategy is difficult to be applied to construct organic micro-/nano-structures. Fortunately, self-assembly, as a bottom-up method, provides a facile and universal method for constructing micro-/nano-structures through intermolecular non-covalent interactions. So far, various CPL-active organic micro-/nano-assemblies have been developed, and the highest |g lum | of the assembly has exceeded 1.4, which is close to the theoretical maximum44. In this section, we will introduce several typical examples:
self-assembly of small molecules;
“In general, self-assembly of organic small molecules provides exciting approaches to constructing CPL-active organic micro-/nano-structures, and the |g lum | can be further amplified by various strategies, particularly the energy and charge transfer.”
self-assembly of π-conjugated polymers;
“CPL-active conjugated polymer assemblies have drawn great attention owing to their well-defined structure modification, tunable luminescent properties, and easy processing63 , 64. They can be constructed through the following two approaches: (1) self-assembly of chiral conjugated polymers, including main-chain chiral conjugated polymers and conjugated polymers with chiral side-chain; (2) doping a chiral conjugated polymers with chiral additives.”
self-assembly on micro-/nanoscale architectures
“Pre-existing micro-/nano-structures can serve as templates to obtain CPL-active micro-/nano-assemblies with specific functions by assembling active molecules into the pores or surface of the templates. Such a method has been considered to be a simple and effective strategy for preparing micro-/nano-structures due to its high preparation efficiency, regular morphologies, and good structural stability. According to the properties of the templates, it can be divided into achiral nanotemplates and chiral nanotemplates.”
Regulation of CPL through external stimuli
Solvent
pH value
Metal ions
Mechanical force
Temperature
Applications of CPL-active organic micro-/nano-structures
CP-OLEDs
Optical information processing
Chemical and biological sensing
Conclusions and perspectives
“Overall, it is foreseeable that the study of CPL at micro-/nanoscale will accelerate the development of CPL-active materials. In future work, more efforts should be made to develop CPL-active organic micro-/nano-structures with high φ a value and study the mechanism of chirality amplification in self-
assembly systems.”