Research Projects

In the last decade, thermally activated delayed fluorescent (TADF) materials have emerged as a forerunner for the next generation Organic light-emitting diodes (OLEDs) due to their internal quantum efficiency (IQE) of 100% via the triplet to singlet reverse intersystem crossing channel (RISC).¹ Efficient RISC is attained by minimizing the energy gap (ΔEST) between the lowest excited singlet (S₁) and triplet (T₁) states. This is typically achieved by designing molecules with a twisted donor (D)-acceptor (A) configuration. Though conventional TADF materials still suffer from low photoluminescence quantum yield (PLQY) due to greater separation of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), and show broad emission, which means less colour purity. To overcome these shortcomings, Hatakeyama et al. introduced multiple-resonance (MR) induced TADF wherein the molecules were designed to take advantage of the complementary resonance effect which enables atomically separated HOMO and LUMO orbitals.² MR-TADF emitters have sufficiently small ΔEST while showing narrowband emission (FWHM ≤ 40 nm) and PLQY near unity. In recent years, many research groups have developed blue and green colour-based MR-TADF emitters, while examples of orange or red MR-TADF emitters are a bit scarce, as they require even lower ΔEST to obtain emission bands in the range of 600-690 nm.³ Some strategies employed to achieve red-emitting MR-TADF include constructing para-boron (B-π-B) in the molecule and increasing the electron-donation ability of the donors.⁴ This proposal aims to fabricate red-emitting OLED by developing MR-TADF materials using phenazine as donor. Phenazine, which has been utilized in conventional TADF and is more powerful than donors like carbazole, phenoxazine, etc.,⁵ has not been employed in MR-TADF. Employment of phenazine in the para-boron framework will increase the electron-donating ability and will potentially lead to a stronger D-A association, leading to a robust system. The purpose of this proposal is to synthesize di- and tetra-boron-embedded molecules that can act as red MR-TADF by using phenazine as a donor and fabricating OLEDs using these emitters. Reference: 1. Nagata, M.; Min, H.; Watanabe, E.; Fukumoto, H.; Mizuhata, Y.; Tokitoh, N.; Agou, T.; Yasuda, T. Angew. Chem. Int. Ed. 2021, 60, 20280-20285 2. Kondo, Y.; Yoshiura, K.; Kitera, S.; Nishi, H.; Oda, S.; Gotoh, H.; Sasada, Y.; Yanai, M.; Hatakeyama, T. Nat. Photonics 2019, 13, 678. 3. Keerthika, P.; Konidena, R. K. Adv. Optical Mater. 2023, 11, 2301732. 4. Hua, T.; Li, N.; Huang, Z.; Zhang, Y.; Wang, L.; Chen, Z.; Miao, J.; Cao, X.; Wang, X.; Yang, C. Angew. Chem. Int. Ed. 2024, 63, e202318433. 5. a) Im, Y.; Kim, M.; Cho, Y. J.; Seo, J.; Yook, K. S.; Lee, J. Y. Chem. Mater. 2017, 29, 1946; b) Tonge, C. M.; Paisley, N. R.; Polgar, A.; Lix, K.; Algar, W. R.; Hudson, Z. M. ACS Appl. Mater. Interfaces 2020, 12, 6525.