Thermally activated triplet exciton release for highly efficient tri-mode organic afterglow

Jibiao Jin,Qiang Zhao,Lele Tang,Yuanyuan Li,Ye Tao,Runfeng Chen,Qingqing Yang,Chao Zheng,He Jiang,Quli Fan,Wei Huang,Kenneth Yin Zhang

doi:10.1038/s41467-020-14669-3

Abstract

Developing high-efficient afterglow from metal-free organic molecules remains a formidable challenge due to the intrinsically spin-forbidden phosphorescence emission nature of organic afterglow, and only a few examples exhibit afterglow efficiency over 10%. Here, we demonstrate that the organic afterglow can be enhanced dramatically by thermally activated processes to release the excitons on the stabilized triplet state (T1*) to the lowest triplet state (T1) and to the singlet excited state (S1) for spin-allowed emission. Designed in a twisted donor–acceptor architecture with small singlet-triplet splitting energy and shallow exciton trapping depth, the thermally activated organic afterglow shows an efficiency up to 45%. This afterglow is an extraordinary tri-mode emission at room temperature from the radiative decays of S1, T1, and T1*. With the highest afterglow efficiency reported so far, the tri-mode afterglow represents an important concept advance in designing high-efficient organic afterglow materials through facilitating thermally activated release of stabilized triplet excitons.

Highlights

Developing high-efficient afterglow from metal-free organic molecules remains a formidable challenge due to the intrinsically spin-forbidden phosphorescence emission nature of organic afterglow, and only a few examples exhibit afterglow efficiency over 10%
DCzB displays a maximum absorption band centered around 380 nm in toluene and 400 nm in film (Fig. 2a) for visible-light excitable photoluminance ascribed to the intramolecular charge transfer (ICT) state of this D–A–D molecule[26,27,28]
This ICT character becomes more apparent in photoluminescence (PL) spectrum in solution, showing a broad PL band that redshifts with the increase of solvent polarity (Supplementary Fig. 10)[28]

Summary

Introduction

Developing high-efficient afterglow from metal-free organic molecules remains a formidable challenge due to the intrinsically spin-forbidden phosphorescence emission nature of organic afterglow, and only a few examples exhibit afterglow efficiency over 10%. Designed in a twisted donor–acceptor architecture with small singlet-triplet splitting energy and shallow exciton trapping depth, the thermally activated organic afterglow shows an efficiency up to 45%. This afterglow is an extraordinary tri-mode emission at room temperature from the radiative decays of S1, T1, and T1*. Organic afterglow efficiency is doomed to be low, considering that only a small part of photoexcited singlet excitons can be transformed to triplet ones through ISC under weak SOC values of purely organic molecules and the nonradiative transitions dominate the triplet exciton decay with the low phosphorescence efficiency at room temperature[8].

Methods

Results

Conclusion