Development of Efficient, Stable and Inexpensive Deep-Red and Near-Infrared OLEDs Based On AIE-Active Thermally Activated Delayed Fluorescence Emitters.

Project Information

DR NIR TADF-OLEDs

Grant agreement ID: 101024874

DOI

10.3030/101024874

Project terminated on 9 July 2023

EC signature date 21 April 2021

Start date 2 November 2021

End date 1 November 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 224 933,76

EU contribution

€ 224 933,76

Coordinated by

THE UNIVERSITY COURT OF THE UNIVERSITY OF ST ANDREWS
United Kingdom

Periodic Reporting for period 1 - DR NIR TADF-OLEDs (Development of Efficient, Stable and Inexpensive Deep-Red and Near-Infrared OLEDs Based On AIE-Active Thermally Activated Delayed Fluorescence Emitters.)

Reporting period: 2021-11-02 to 2023-11-01

Summary of the context and overall objectives of the project

This action aimed to develop efficient, stable, and inexpensive deep-red (DR) and near-infrared (NIR) organic light-emitting diodes (OLEDs) using aggregation-induced emission (AIE)-active thermally activated delayed fluorescence (TADF) emitters. The development of highly efficient DR and NIR TADF OLEDs is challenging, primarily due to the inherent limited brightness of DR and NIR emissive materials, which tend to have naturally low photoluminescence quantum yields (PLQY). This work thus aims to overcome the challenges posed by the low PLQYs of DR and NIR emissive materials by developing new emitters containing boron-dominant AIE and TADF characteristics.

The significance of this action lies in the potential applications of these DR and NIR OLEDs beyond their use in displays and lighting, encompassing a wide array of domains such as bioimaging, photodynamic therapy, night vision technology, secure information displays, and optical communication.

The objectives of this Marie Skłodowska Curie Action (MSCA) have been (1) to develop DR and NIR TADF emitters exhibiting high PLQY and (2) to demonstrate superior external quantum efficiency (EQE) in non-doped OLEDs, which will be accomplished through efficient AIE-active emitters, as these emitters show enhanced PLQY in the condensed phase.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project consisted of four work packages (WPs). In WP1, we modeled four proposed target deep-red (DR) boron diiminate (BDI) emitters containing two strong donor 9,9-dimethyl-9,10-dihydroacridine (DMAC) using DFT/TD-DFT calculations at the PBE0/6-31G(d,p) level of theory in the gas phase. These calculations indicated that these emitters have the potential to be TADF emitters. WP2 involved the synthesis of these TADF BDI emitters and their chemical characterization using modern analytical techniques such as NMR spectroscopy, ESI-HRMS, XRD, and HPLC. In WP3, we investigated the detailed photophysical and electrochemical properties of the BDI TADF emitters to assess their suitability for OLED fabrication. To ensure high purity, the BDI emitters were sublimed and the purity evaluated using melting point measurements, elemental analysis, and HPLC analysis. Photophysical measurements were conducted both in a solution state and as films doped in 10 wt% PMMA, as well as neat films. The optical gap of the BDI emitters was determined from UV-Vis absorption spectra measured in toluene, and singlet and triplet state energies were estimated from the steady-state PL measurements in air and nitrogen at low temperatures. The aggregation-induced emission (AIE) properties of these emitters were demonstrated in THF/water or CHCl3/hexane solvent mixtures, showing a significant increase in emission from 4- to 32-fold in the aggregate state compared to the solution state. Oxidation and reduction potentials were measured by cyclic voltammetry. Unfortunately, the photoluminescence quantum yields (PLQYs) of the emitters were relatively low, measuring below 39% in the 10 wt% doped films in PMMA and even lower as neat films (below 11%). As a result, these compounds were not suitable for OLEDs, and OLED devices were not fabricated due to cost-benefit considerations, as initially planned in WP4. However, it is worth noting that these emitters displayed mechanochromism and enhanced emission induced by crystallization, offering interesting properties beyond their TADF and AIE properties.

Results of this Marie Skłodowska Curie Action (MSCA) project will be published in forthcoming papers on the synthesis of boron diiminate (BDI) emitters with aggregation-induced emission and thermally activated delayed fluorescence characteristics.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Beyond the state of the art: The project has made progress beyond the state-of-the-art in the field of development of DR and NIR TADF emitters. (a) Utilizing advanced DFT/TD-DFT calculations for the modelling of potential DR boron diiminate (BDI) emitters, representing a cutting-edge approach in material design for OLEDs. (b) Successfully synthesizing and characterizing four novel BDI emitters. (c) Conducting optoelectronic characterization, revealing valuable insights into their emission properties. These emitters not only exhibit TADF behaviour but also demonstrate attributes such as aggregation-induced enhanced emission. These compounds unexpectedly showed mechanochromism, and enhanced emission induced by crystallization. The combination of these findings not only expanded the scientific understanding in the field of materials development but also provides valuable insights into the potential applications and limitations of these new BDI emitters. While they may not be directly applicable to OLED technology due to low PLQYs, their unique properties may find use in other emerging technologies or research areas.

Expected results: The project is expected to result in a forthcoming paper that will disseminate knowledge about the synthesis of BDI emitters with AIE and TADF characteristics. This will significantly contribute to the OLED research community in understanding of these BDI emitting materials.

Potential Impacts: The project has advanced our understanding of DR and NIR TADF-emitting materials, providing valuable insights into the synthesis, characterization, and optoelectronic properties of BDI emitters. Although these emitters may not find immediate application in OLEDs due to low PLQYs, this research provides insight for future materials design of efficient DR and NIR OLED materials. These improvements could have a positive impact on crucial sectors like healthcare, security, and communication, as DR and NIR-emitting OLEDs are essential for applications such as bioimaging, photodynamic therapy, night vision, secure displays, and optical communication.

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