Azulene as a Modular Platform for Next-Generation MR-TADF Emitters

• Applicant: Dr. Martin Christian Dietl
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 574466748

The development of efficient, color-pure, and sustainable OLED emitters is a key challenge in materials science. Multiresonant thermally activated delayed fluorescence (MR-TADF) has proven to be a key strategy for maximizing the light output of fully organic emitter systems without the use of rare or toxic metals. However, existing MR-TADF emitters are based almost exclusively on benzoid aromatic hydrocarbons. This project proposes for the first time the use of azulenes, a topologically asymmetric, non-alternating aromatic compound, as a molecular platform for MR-TADF emitters. Azulene has an unconventional distribution of frontier orbitals (HOMO at positions 1,3,5,7; LUMO at 2,4,6,8), which enables intramolecular electronic decoupling within a rigid π system, a prerequisite for MR-TADF. Based on comprehensive quantum chemical preliminary studies, a virtual library of 150 azulene derivatives with targeted substitution was created and investigated for essential MR-TADF criteria such as low singlet-triplet energy difference, high oscillator strengths, and localized transition densities. From this library, 13 promising candidates were identified, whose synthesis, characterization, and OLED integration will be carried out in an integrative work program. The project combines organic synthesis, spectroscopy, quantum chemistry, and device fabrication in three closely interlinked work packages. Functionalized azulenes are produced by position-selective substitution of donor and acceptor units, characterized photophysically and electrochemically, and integrated into OLEDs. Particular attention is paid to the experimental determination of the singlet-triplet energy difference, the efficiency of the TADF process, and the optoelectronic device parameters. Complementary DFT calculations allow the theoretical description of structure-property correlations of these systems. By establishing azulenes as a novel MR-TADF framework, the project makes a conceptual contribution to expanding the molecular design logic in organic photonics, away from conventional alternating atoms to non-alternating systems. The project also forms the basis for the development of an independent research profile at the interface of molecular design, quantum chemistry, and functional materials.

• DFG Programme: WBP Fellowship
• International Connection: Japan
• Host: Professor Dr. Takuji Hatakeyama