The manipulation of the singlet-triplet energy gap (ΔES1T1) is an active area of research in the field of organic semiconductor materials. In polycyclic heteroaromatic (PHA) emitters, which possess a great potential for application in ultra-high-definition displays, the origin of a small ΔES1T1 and its relationship with molecular structure still remain poorly established.
To address these challenges, Prof. Xiao-Hong Zhang, Prof. Xian-Kai Chen and Prof. Kai Wang from the Institute of Functional Nano & Soft Materials (FUNSOM) at Soochow University, together with Prof. Chihaya Adachi from Kyushu University, have developed a novel physical picture that can precisely describe ΔES1T1 in PHA materials based on configuration-interaction theory: ΔES1T1 positively depends both on 2KHL (where KHL is the exchange energy between the HOMO and LUMO) and on the energy gap between the LUMO and LUMO+1 levels (ΔELUMO-LUMO+1). This physical picture is validated over a series of 100 reported PHA emitters with different heteroatoms and emissive colours. The proof-of-concept molecule has been synthesized and characterized experimentally to further confirm the validity of this physical picture. The corresponding OLED exhibited a remarkable maximum external quantum efficiency of ca. 40% with a largely suppressed roll-off (4.7%) at 1000 cd m-2. Overall, this work provides a new physical picture to not only modulate ΔES1T1 in emerging PHA emitters but also design and screen such materials with small ΔES1T1, which will accelerate the development of such high-efficiency systems. The related research results were published online in Nature Materials(DOI: 10.1038/s41563-025-02309-4). Co-first authors include postdoctoral researcher Rajat Walia, Ph.D. candidate Xin Xiong, and Assoc. Prof. Xiao-Chun Fan from FUNSOM.
Figure 1. Physical picture for reducing ΔES1T1.
Figure 2. Photophysical and electroluminescence properties of the proof-of-concept molecule.
Link to paper：https://www.nature.com/articles/s41563-025-02309-4
Title: Achieving small singlet–triplet energy gaps in polycyclic heteroaromatic emitters
Authors: Rajat Walia, Xin Xiong, Xiao-Chun Fan, Ting-Feng Chen, Hui Wang, Kai Wang*, Yi-Zhong Shi, Xun Tang, Jean-Luc Bredas, Chihaya Adachi*, Xian-Kai Chen*, and Xiao-Hong Zhang*
Editor: Guo Jia