Controlling the thermally activated delayed fluorescence of axially chiral organic emitters and their racemate for information encryption.

Bingjia Xu,Zicun Song,Cong Liu,Fengqiang Sun,Zujin Zhao,Zhenguo Chi,Changlin Su,Yi Zhang,Cao Xu,Lijun Zhong,Qiqi Ban,Qingqing Zhang,Minmin Zhang,Long Jiang,Guang Shi

doi:10.1039/d1sc04738h

Abstract

A pair of axially chiral organic enantiomers were facilely prepared through a one-pot sequential synthesis. They exhibit circularly polarized luminescence activities and have thermally activated delayed fluorescence (TADF) and aggregation-induced emission enhancement properties. Meanwhile, these two enantiomers present remarkable and reversible thermochromism in the crystalline state, enabling dual-colour TADF switching between orange and red. However, when they form cocrystals, the resulting racemate shows opposite thermochromic behaviors. These intriguing results probably emanate from their different optical activities, leading to distinct molecular packing modes and molecular conformation variations. Moreover, information encryption based on thermochromism of organic enantiomers and their racemate has been presented for the first time. This work may expand the application scope of chiral organic luminogens and pave a new way to construct intelligent luminescent systems.

Highlights

They exhibit circularly polarized luminescence activities and have thermally activated delayed fluorescence (TADF) and aggregation-induced emission enhancement properties. These two enantiomers present remarkable and reversible thermochromism in the crystalline state, enabling dual-colour TADF switching between orange and red
The resulting enantiomers exhibited CP-TADF characteristics and aggregation-induced emission enhancement (AIEE) properties. They displayed remarkable and reversible thermochromism in the crystalline state, enabling dual-colour TADF switching between orange and red
The enantiomers (R)-CzACN and (S)-CzACN with circular polarized luminescence (CPL) and AIEE properties exhibit dual-colour TADF switching between orange and red a er being heated and fumed, which may be applied to anti-counterfeiting and optoelectronic devices

Summary

Introduction

Chiral organic luminophores have received considerable attention recently due to their promising applications in optoelectronic devices, optical data storage, bioencoding, quantum computing, and asymmetric photochemical synthesis.[1,2,3,4] In general, they can be constructed by introducing chiral luminescent center(s) or using the concept of chiral perturbation by tethering an enantiopure unit to a chromophore.[4,5,6] Under the guidance of these design strategies, lots of chiral organic luminogens with unique luminescence properties such as thermally activated delayed uorescence (TADF), roomtemperature phosphorescence, and a erglow have been sequentially developed in the last few years.[2,4,7,8,9,10,11,12,13,14] Despite theseNotably, purely organic materials with circularly polarized thermally activated delayed uorescence (CP-TADF) have attracted great interest in recent years.[4,7,23,24,25,26,27] They can harvest both singlet and triplet excitons and produce CP light directly, which are favorable for elevating the internal quantum efficiencies of organic light-emitting diodes (OLEDs) and diminishing the electroluminescence absorption loss on the polarizer to reduce energy consumption in OLED displays.[28,29,30] probably due to the more complicated molecular design than common TADF emitters, only a few organic compounds with CP-TADF characteristics have been reported to date. We present a pair of CP-TADF active organic enantiomers and their racemate, which show different thermochromic behaviors, and demonstrate the possibility of their application in information encryption.

Results

Conclusion