Through‐Space Charge‐Transfer Polynorbornenes with Fixed and Controllable Spatial Alignment of Donor and Acceptor for High‐Efficiency Blue Thermally Activated Delayed Fluorescence

Pillararene-Induced Intramolecular Through-Space Charge Transfer and Single-Molecule White-Light Emission

The fabrication of single-molecule white-light emission (SMWLE) materials has become a highly studied topic in recent years and through-space charge transfer (TSCT) is emerging as an important concept in this field. However, the preparation of ideal TSCT-based SMWLE materials is still a big challenge. Herein, we report a bifunctional pillar[5]arene (TPCN-P5-TPA) with a linear donor-spacer-acceptor structure and aggregation-induced emission (AIE) property. The bulky pillar[5]arene between the donor and acceptor induces a twisted conformation and a non-conjugated structure, resulting in intramolecular TSCT. In addition, the AIE feature and pillar[5]arene cavity endow TPCN-P5-TPA with responsiveness to viscosity and polar guests, by which the TSCT emission is triggered. The combination of blue locally-excited state emission and yellow TSCT emission of TPCN-P5-TPA generates SMWLE. Therefore, we provide a new and versatile strategy for the construction of TSCT-based SMWLE materials.

Asymmetrical-Dendronized TADF Emitters for Efficient Non-doped Solution-Processed OLEDs by Eliminating Degenerate Excited States and Creating Solely Thermal Equilibrium Routes

The mechanism of thermally activated delayed fluorescence (TADF) in dendrimers is not clear. We report that fully‐conjugated or fully‐nonconjugated structures cause unwanted degenerate excited states due to multiple identical dendrons, which limit their TADF efficiency. We have synthesized asymmetrical “half‐dendronized” and “half‐dendronized‐half‐encapsulated” emitters. By eliminating degenerate excited states, the triplet locally excited state is ≥0.3 eV above the lowest triplet charge‐transfer state, assuring a solely thermal equilibrium route for an effective spin‐flip process. The isolated encapsulating tricarbazole unit can protect the TADF unit, reducing nonradiative decay and enhancing TADF performance. Non‐doped solution‐processed devices reach a high external quantum efficiency (EQE_max) of 24.0 % (65.9 cd A⁻¹, 59.2 lm W⁻¹) with CIE coordinates of (0.24, 0.45) with a low efficiency roll‐off and EQEs of 23.6 % and 21.3 % at 100 and 500 cd m⁻².

Simultaneously Enhanced Reverse Intersystem Crossing and Radiative Decay in Thermally Activated Delayed Fluorophors with Multiple Through-space Charge Transfers

Thermally activated delayed fluorescence (TADF) materials with through-space charge transfers (CT) have attracted particularly interest recently. However, the slow reverse intersystem crossing (RISC) and radiative decay always limit their electroluminescence performances. Herein, TADF molecules with ortho-linked multiple donors-acceptor (ortho-D_n -A) motif are developed to create near-degenerate excited states for the reinforcement of spin-orbit coupling. The incorporation of both through-bond and through-space CT enlarges oscillator strength. The optimal ortho-D₃ -A compound exhibits a photoluminescence quantum yield of ca. 100 %, a high RISC rate of 2.57×10⁶  s^-1 and a high radiative decay rate of 1.00×10⁷  s^-1 simultaneously. With this compound as the sensitizer, a TADF-sensitized-fluorescent organic light-emitting diode shows a maximum external quantum efficiency of 31.6 % with an ultrapure green Commission Internationale de L'Eclairage y coordinate value of 0.69.

π-Stacked Donor-Acceptor Dendrimers for Highly Efficient White Electroluminescence

π-Stacked dendrimers consisting of cofacially aligned donors and acceptors are developed by introducing three dendritic teracridan donors with orthogonal configuration and three triazine acceptors in periphery of hexaphenylbenzene skeleton. The dendritic structure and orthogonal configuration of teracridan not only make their outer acridan segments approaching to acceptor in close distance, but also fix donor and acceptor in face-to-face alignment, leading to through-space charge transfer emission with thermally activated delayed fluorescence (TADF) effect. By regulating charge transfer strength via substituent effect of acceptor, emission color of the dendrimers can be tuned from blue to yellow/red region. Solution-processed two-color white organic light-emitting diodes (OLEDs) based on blue and yellow π-stacked donor-acceptor dendrimers exhibit the maximum external quantum efficiency of 20.6 % and maximum power efficiency of 58.9 lm W^-1 , representing the state-of-the-art efficiency for all-TADF white OLEDs by solution process.

Face-to-Face Orientation of Quasiplanar Donor and Acceptor Enables Highly Efficient Intramolecular Exciplex Fluorescence

Intramolecular through-space charge-transfer (TSCT) excited states have been exploited for developing thermally activated delayed fluorescence (TADF) emitters, but the tuning of excited state dynamics by conformational engineering remains sparse. Designed here is a series of TSCT emitters with precisely controlled alignment of the donor and acceptor segments. With increasing intramolecular π-π interactions, the radiative decay rate of the lowest singlet excited state (S₁ ) progressively increased together with a suppression of nonradiative decay, leading to significantly enhanced photoluminescence quantum yields of up to 0.99 in doped thin films. A high-efficiency electroluminescence device, with a maximum external quantum efficiency (EQE) of 23.96 %, was achieved and maintains >20 % at a brightness of 1000 cd m^-2 . This work sheds light on the importance of conformation control for achieving high-efficiency intramolecular exciplex emitters.