Engineering Intramolecular π‐Stacking Interactions of Through‐Space Charge‐Transfer TADF Emitters for Highly Efficient OLEDs with Improved Color Purity

Abstract

Purely organic compounds with thermally activated delayed fluorescence (TADF) are promising sustainable emitters for organic light‐emitting diodes. But the simultaneous realization of a high efficiency, short lifetime, and good color purity in single TADF molecule remains challenging. Herein it is reported that the confinement of rigid and planar N‐ and B‐centered donor and acceptor in sandwich‐type structures, named BNB‐m and BNB‐p, can lead to green TADF emissions with up to unity efficiency and improved color purity from through‐space charge‐transfer excited states. The full width at half maximum of 58 nm (0.28 eV) for BNB‐m is significantly smaller than those for most of the TADF emitters having a twisted donor‐acceptor structure. Single‐crystal structures, NMR spectroscopy, and theoretical simulations manifest the presence of strong noncovalent π‐stacking interactions in BNB‐m which account for the reduced intramolecular motions and enhanced through‐space electronic coupling. With a relatively short delayed fluorescence lifetime of 11 µs, the emitter BNB‐m demonstrates attractive green electroluminescence with a maximum external quantum efficiency (EQE) of 34.9% and an EQE of 27.4% at 1000 cd m−2. This work validates a promising molecular design to TADF emitters which can realize a balanced emission property in terms of color purity and emission lifetime.

Regulating the Distance Between Donor and Acceptor in Space‐Confined Through‐Space Charge Transfer Emitters for Fast Radiative Decays and High‐Efficiency Organic Light‐Emitting Diodes With Low Efficiency Roll‐Offs

“…Li et al previously reported doubledecker TSCT molecules featuring donor/acceptor/donor or acceptor/donor/acceptor sandwich structures, which show strong through-space electronic interactions and noticeable 1 CT absorption bands. [37][38][39] It is worth noting that emitters 1-3 with a donor/acceptor sandwich structure also show 1 bands, indicating the molecular design presented here is effective to promote through-space electronic interactions.…”

“…Emitter R was synthesized and characterized in a previous report. [54] various bridges, such as 9,9-dimethyl-9,10-dihydroacridin or phenoxazine, [32] carbazole, [33][34][35][36][37][38][39] triptycene, [24] acenaphthene, [40] [2.2]paracyclophane, [41] dithia [3.3]paracyclophane, [42] and aromatic macrocycle, [43] have been employed to develop intramolecular TSCT emitters with cofacially aligned donor/acceptor. In these emitters, neither the donor nor the acceptor is fixed, which would cause non-radiative deactivation of the emissive 1 CT state by intramolecular rotation or vibration.…”

Recent advances and prospects for organoboron-based thermally activated delayed fluorescence emitters

“…With a relatively short delayed fluorescence lifetime of 11 ms, 73 demonstrated attractive green electroluminescence with an EQE max of 34.9% and an EQE of 27.4% at 1000 cd m À2 . 49 Because of the weak electron-accepting ability of boron acceptors, the TADF materials discussed above tend to show excellent performance in blue OLEDs. The red light-emitting materials remain limited.…”

“…With a relatively short delayed fluorescence lifetime of 11 μs, 73 demonstrated attractive green electroluminescence with an EQE max of 34.9% and an EQE of 27.4% at 1000 cd m −2 . 49…”

Metal‐Perturbed Multiresonance TADF Emitter Enables High‐Efficiency and Ultralow Efficiency Roll‐Off Nonsensitized OLEDs with Pure Green Gamut

“…[11][12][13][14][15][16] A number of molecules with short-lived delayed fluorescence of <10 µs have been obtained. [17][18][19][20][21][22] However, both phosphorescent metal complexes and purely organic TADF compounds have unsatisfactory color purity, as revealed by the large full width at half maximum (FWHM) values. Although it has been well recognized that increasing molecular rigidity and thus suppressing the excited state structural changes are useful for narrowing the emission spectral bandwidth, emission color purity of these two types of emitters is not as good as the quantum dots and perovskite emitters.…”