Acceptor-Donor-Acceptor π -Stacking Boosts Intramolecular Through-Space Charge Transfer towards Efficient Red TADF and High-Performance OLEDs

Abstract

Organic push-pull systems featuring through-space charge transfer (TSCT) excited states have been disclosed to be capable of exhibiting thermally activated delayed fluorescence (TADF), but to realize high-efficiency long-wavelength emission still remains a challenge. Herein, we report a series of strongly emissive orange-red and red TSCT-TADF emitters having (quasi)planar and rigid donor and acceptor segments which are placed in close proximity and orientated in a cofacial manner. Emission maxima (λem) of 594−599 nm with photoluminescence quantum yields (PLQYs) of up to 91% and delayed fluorescence lifetimes of down to 4.9 μs have been achieved for new acceptor-donor-acceptor (A-D-A) molecules in doped thin films. The presence of multiple acceptors and the strong intramolecular π-stacking interactions have been unveiled to be crucial for the efficient low-energy TSCT-TADF emissions. Organic light-emitting diodes (OLEDs) based on the new A-D-A emitters demonstrated electroluminescence with maximum external quantum efficiencies (EQEs) of up to 23.2% for the red TSCT-TADF emitters. An EQE of 18.9% at the brightness of 1000 cd m-2 represents one of the highest values for red TADF OLEDs. This work demonstrates a modular approach for developing high-performance red TADF emitters through engineering through-space interactions, and it may also provide implications to the design of TADF emitter with other colours.

Donor Extension on Spiro‐Acridine Enables Highly Efficient TADF‐OLEDs with Relieved Efficiency Roll‐Off

“…Spiro-acridine (SA) as one of the most popular building blocks is well adopted in different types of TADF compounds such as twisted donor-acceptor (D-A), space confined charge transfer and multi-resonance (MR) emitters. [23][24][25][26][27][28][29][30][31] The well demonstrated electroluminescent performance of the TADF molecules pronounces the superiority of SAs. The unique rigid cross configuration of SAs leads to excellent thermal stability and well suppressed non-radiative decay.…”

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

“…previously reported double‐decker 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. [ 37–39 ] It is worth noting that emitters 1–3 with a donor/acceptor sandwich structure also show 1 CT absorption 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.…”

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.…”