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BIT Makes Breakthrough in Field of Purely Organic Doping Phosphorescence Materials

release date :2019-11-17 08:37:00  |   [ close window ]ViewCount:

  Beijing Institute of Technology, Oct 29th, 2019: Recently, professor Dong Yuping and associate professor Cai Zhengxu from the School of Materials Science and Engineering of Beijing Institute of Technology (BIT) successfully designed to prepare a series of ultralong organic doping phosphorescence materials. Relevant results are published in the Journal of physical chemistry Letters (link: https://pubs.acs.org/doi/full/10.1021/acs.jpclett.9b02411 ), a top academic magazine. Lei Yunxiang, doctoral student of the School of Materials Science and Engineering of BIT, is the first author of the paper. Professor Dong Yuping and Cai Zhengxu are co-corresponding authors.

 

  Due to their delayed luminescent properties which are not possessed by fluorescent materials, materials with organic room temperature phosphorescent properties have an alluring application prospect in the fields of anti-fake, biological detection and photochemistry. Compared with inorganic precious metal phosphorescent materials, organic phosphorescent materials have advantages of low cost, strong plasticity and low toxicity. Conventional organic phosphorescent materials contain carbazole, carbonyl or halogen heavy atoms such as chlorine. Recently, a Japanese professor Adachi reported a purely organic host-guest system with lutralong luminescence, but the host and guest of such materials must be one donor and the other acceptor. In order to expand the usability of host and guest, the group of Dong Yuping first demonstrated a new guest molecule DOB with a donor moiety (triphenylamine, TPA) and an acceptor moiety (benzo nitrile). The guest molecule shows weak fluorescence and nonphosphorescence at room temperature. Two precursors of DOB (TPA and 4-(cyan methyl) benzo nitrile, CBN) are selected as donor host and acceptor host, respectively. The interaction between acceptor and donor hosts will occur between the tramline unit in DOB and the host CBN, and the phenyl acetonitrile unit in DOB will also interact with the host TPA as acceptor and donor, respectively. And because DOB contains tramline and phenyl acetonitrile, it is easy for DOB to enter the main lattice. The doped materials containing CBN/DOB and TPA/DOB were obtained by recrystallization (guest: main molar body =0.0005:1). Compared with the original host possessing solely weak fluorescence, the new doped material has an enhanced fluorescence (Ф = 63-76%) and room-temperature phosphorescence (Ф = 7.6-14.5%, tau =119ms -317ms). The authors thinks that the strong intermolecular interactions mainly determined by both the crystalline state and molecular energy levels accounted for their persistent luminescence.

  

  In addition, the author also explored other compounds featuring similar structure to TPA or CBN. These compounds, as the hosts, can be doped with DOB to obtain doped materials with fluorescence and phosphorescence under ambient conditions, indicating that the new system developed by the author has strong universality. Besides, the material shows a high environmental stability to water, light and heat.

  

Figure 1 (a) molecular structure of guest and host molecules.

(b) CBN, TPA, CBN/DOB, and TPA/DOB powders before and after the removal of irradiation

(c) Fluorescence spectra of CBN, TPA, and DOB crystalline powders and their doped crystalline powders at room temperature.

(d) Delayed phosphorescence spectra of DOB powder and doped crystalline powders at room temperature. (image from ACS)

Figure 2 Jablonski diagram for a TPA/DOB- and CBN/DOB-doped crystalline powders. S1, D and T1, D indicate the singlet and triplet states of TPA, S1, A and T1, A indicate the singlet and triplet states of CBN, S1, G and T1, G indicate the singlet and triplet states of the guest molecule (DOB), and S1, C and T1, C indicate the singlet and triplet states of the charge transfer state formed between host and guest molecules.

(image from ACS)

The research was supported by the National Natural Science Foundation of China (51803009,51673024, 51328302, 21404010) and the Academic Start-Up Fund of BIT.

 

Introduction to the organic luminescent materials research group:

  Dong Yuping, professor at the school of Materials Science and Engineering of BIT,winner of the State Natural Science Prize, is mainly engaged in the research of organic luminescent materials.

  Cai Zhengxu, associate professor at school of Materials Science and Engineering of BIT, got bachelor's degree in Wuhan University, completed both graduate and doctoral study in the Institute of Chemistry of Chinese Academy of Sciences, and finished post-doctoral research in University of Chicago.

  He is mainly engaged in the research of luminescent materials with field effect and AIE characteristics, having published many academic papers as the first author in high-level journals such as j. Am. Chem. Soc., Angew. Chem., Int. Ed. Chem.

 

News Source: School of Materials Science and Engineering

Editor: News Agency of BIT

Translator: News Agency of BIT, Miao Yufei

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