Sterically Wrapped Multiple Resonance Fluorophors for Suppression of Concentration Quenching and Spectrum Broadening

Abstract

Multiple resonance (MR) emitters are promising for highly efficient organic light-emitting diodes (OLEDs) with narrowband emission;h owever,t hey still face intractable challenges with concentration-caused emission quenching, exciton annihilation, and spectral broadening. In this study, sterically wrapped MR dopants with af luorescent MR core sandwiched by bulk substituents were developed to address the intractable challenges by reducing intermolecular interactions. Consequently,h igh photo-luminance quantum yields of ! 90 %a nd small full width at half maximums (FWHMs) of 25 nm over aw ide range of dopant concentrations (1-20 wt %) were recorded. In addition, we demonstrated that the sandwiched MR emitter can effectively suppress Dexter interaction when doped in at hermally activated delayed fluorescence sensitizer,eliminating exciton loss through dopant triplet. Within the above dopant concentration range,t he optimal emitter realizes remarkably high maximum external quantum efficiencies of 36.3-37.2 %, identical small FWHMs of 24 nm, and alleviated efficiency roll-offs in OLEDs.

73‐1: Invited Paper: Decoration Strategy in Para Boron Position: An Effective Way to Achieve Ideal Multi‐Resonance Emitters

“…Moreover, inspired by the 2F-BN structure, a more advanced molecular motif named Ph-BCz-BN is further proposed by our group through adopting a peripheral benzene ring on the para position of the B-substituted phenyl in BCz-BN core to construct the high-purity, high-efficiency, quenching-resistant and stable MR emitters (Figure 2). [5] As demonstrated above, the introduction of peripheral benzene ring could not only increase the low-frequency rotational components, but also provide more easy-to-modify reaction sites to construct MR molecules with different functions. As exemplified by S-Cz-BN and D-Cz-BN, [5] where bulk substituents were introduced onto Ph-BCz-BN, the sterically wrapped MR dopants could effectively solve the challenges of concentration-caused emission quenching, exciton annihilation, and spectral broadening by enlarging the intermolecular distance between the MR-emitting core and the adjacent molecules.…”

“…[5] As demonstrated above, the introduction of peripheral benzene ring could not only increase the low-frequency rotational components, but also provide more easy-to-modify reaction sites to construct MR molecules with different functions. As exemplified by S-Cz-BN and D-Cz-BN, [5] where bulk substituents were introduced onto Ph-BCz-BN, the sterically wrapped MR dopants could effectively solve the challenges of concentration-caused emission quenching, exciton annihilation, and spectral broadening by enlarging the intermolecular distance between the MR-emitting core and the adjacent molecules. With the optimal emitter of D-Cz-BN, the TSF-OLED showed remarkably high EQEmaxs of 36.3-37.0% over a large dopant concentration range of 1 wt%-20 wt%, with significantly relieved efficiency roll-off and a small FWHM of merely 24 nm.…”

“…Chemical structures, photophysical properties and device performances of S-Cz-BN, D-Cz-BN (Adapted with permission. [5] Copyright 2021, Wiley-VCH), BN-CP1, BN-CP2 (Adapted with permission. [7] Copyright 2021, Wiley-VCH), TW-BN, TPh-BN, pCz-BN, and mCz-BN (Adapted with permission.…”

Synergetic Insulation and Induction Effects Selectively Optimize Multiresonance Thermally Activated Delayed Fluorescence

“…Therefore, high structural rigidity and effective ICT can be integrated to realize narrowband TADF emission [23]. Through conjugation extension and functional modification, blue [27][28][29][30][31][32][33], green [34][35][36][37][38][39], yellow [40,41], and red [42] TADF emitters were developed, whose device efficiencies were comparable to those of the most efficient counterparts, e.g., the maximum external quantum efficiencies (EQE, η EQE ) >20%. Modifying MR core with the electroactive D and A groups can markedly improve device performance but simultaneously induce bathochromic shifts and increased FWHM (>40 nm).…”

Pressure-Induced Local Excitation Promotion: New Route toward High-Efficiency Aggregate Emission Based on Multimer Excited State Modulation

“…Organic luminescent materials have been the focus of research for decades because of their structural abundance, flexibility of molecular design, and superior properties. − However, compared to their monomeric counterparts, solid state organic luminophores usually suffer from emission quenching due to the complicated interactions and severe electronic coupling in molecular stacking, which hinders their practical applications. − To address this issue, an aggregation-induced emission (AIE) strategy has been developed to improve single-molecule emission by restricting intramolecular motions. − In AIE systems, the single-molecule emissive transitions are limitedly disturbed, preserving the excellent optical properties of monomeric luminophores in aggregated states. Other strategies are also developed following this idea. − Nonetheless, more generally, intermolecular interactions such as π–π interaction, hydrogen bonding, the hydrophobic effect, and electrostatic attraction commonly exist in molecular aggregates, − naturally causing the formation of multimeric aggregated excited states, − which makes it extremely challenging to conserve single-molecule emission. Because the multimer excited states are usually non-emissive or weakly emissive in essence, achieving efficient emission in such aggregates is particularly difficult.…”