Blue Thermally Activated Delayed Fluorescence with Sub‐Microsecond Short Exciton Lifetimes: Acceleration of Triplet–Singlet Spin Interconversion via Quadrupolar Charge‐Transfer States. Issue 13 (12th May 2022)

• Record Type: Journal Article
• Authors: Min, Hyukgi; Park, In Seob; Yasuda, Takuma
• Is Part Of: Advanced optical materials. Volume 10:Issue 13(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-05-12
• Subjects: donor–acceptor systems -- organic light‐emitting diodes -- quadrupolar systems -- spin–orbit coupling -- thermally activated delayed fluorescence; Optical materials -- Periodicals; Photonics -- Periodicals; 620.11295
• DOI: 10.1002/adom.202200290
• Languages: English
• ISSNs: 2195-1071

Abstract

Abstract: Exciton lifetime is a critical factor in determining the performance of optoelectronic functional systems and devices. Thermally activated delayed fluorescence (TADF) emitters that can concurrently achieve a high fluorescence quantum yield and short exciton lifetime are desirable for application in organic light‐emitting diodes (OLEDs) with suppressed efficiency roll‐off. Herein, phenoxaborin and xanthone‐cored TADF emitters with quadrupolar electronic structures are reported to exhibit sub‐microsecond TADF lifetimes as short as 650 and 970 ns, respectively, while preserving high fluorescence quantum yields. By extending the El‐Sayed rule to the quadrupolar π‐systems, the contribution of doubly degenerate charge‐transfer excited states induced by dual donor units can enhance the spin–orbit coupling between them, leading to a spin‐flip acceleration between the excited triplet and singlet states. This electronic feature is advantageous for mitigating exciton annihilation processes in the emission layer, thereby reducing the efficiency roll‐offs in OLEDs. Consequently, a high external electroluminescence quantum efficiency over 20% can be retained, even under operating the device at a high luminance of 1000 cd m −2 . Abstract : A rational molecular design of thermally activated delayed fluorescence (TADF) emitters for enabling ultrashort exciton lifetimes (<1 µs) is presented. The effective utilization of quadrupolar π‐systems, which can induce degenerate charge‐transfer excited states contributing to the spin‐flip acceleration, endows the emitters with a high luminescence efficiency and short emission lifetime concurrently.