Design and synthesis of multi-resonant thermally activated delayed fluorescence materials and chiral emitters

Abstract

Multi-resonant thermally activated delayed fluorescence (MR-TADF) materials have been widely investigated as emitters in organic light-emitting diodes (OLEDs) due to their bright and narrowband emission that results from their rigid structures and short-range charge transfer (SRCT) character of the emissive excited state. However, their planar geometry and relatively large singlet-triplet energy gap lead to, respectively, severe aggregation-caused quenching (ACQ) and slow reverse intersystem crossing (RISC). This thesis is partially centered on developing new MR-TADF emitters to solve these two problems.

Using chiral compounds that can emit circularly polarized luminescence (CPL) is beneficial for their potential to increase the light out-coupling efficiency of OLEDs that use anti-glare filters. This thesis also investigates the design of chiral MR-TADF emitters, aiming to achieve bright, narrowband emission showing a strong CPL signal.

Chapter 1 introduces what is an OLED and how it works. The design of TADF emitters along with overviews of the development of heavy-atom-based MR-TADF emitters and chiral MR-TADF emitters are also discussed.

Chapter 2 presents the design of two MR-TADF emitters, TPPO-tBu-DiKTa and TPA-tBu-DiKTa, and the effect of twisted peripheral groups on the alleviation of ACQ and improvement of RISC.

Chapter 3 demonstrates two heavy-atom-based MR-TADF emitters, DiKTaSe and tBuCz-DiKTaSe, and the contribution of heavy atom effect to the TADF performance and efficiency roll-off in OLEDs.

Chapter 4 describes two chiral MR-TADF emitters tBuPh-BN and DPA-tBuPh-BN and their TADF and chiroptical properties.

Chapter 5 demonstrates the design of a propeller-shaped triple helicene DiKTa3 and explores its chiroptical properties through Density Functional Theory calculations.

Chapter 6 reports the design of a series of TADF polymers. Their TADF performance is investigated. The formation of chiral phase in polymer film through blending with chiral additives and their chiroptical properties are explored.

Chapter 7 includes the experimental methods used in this thesis.