Herein, we demonstrate that the strategic implementation of electron-accepting tricoordinate boron and electron-donating carbazole subunits into polycyclic aromatic hydrocarbons (PAHs) produces a family of attractive full-color luminophores that can emit narrowband and efficient thermally activated delayed fluorescence (TADF). A versatile modular design for these boron- and carbazole-embedded PAHs can facilitate the systematic modulation of their photophysical and optoelectronic properties. Organic light-emitting diodes that utilize these PAHs as TADF emitters demonstrate narrowband electroluminescence from blue to red, achieving high maximum external quantum efficiencies of 29.3%, 31.8%, and 22.0% for blue, green, and red, respectively.

Aromatic organic deep-blue emitters that exhibit thermally activated delayed fluorescence (TADF) can harvest all excitons in electrically generated singlets and triplets as light emission. However, blue TADF emitters generally have long exciton lifetimes, leading to severe efficiency decrease, i.e., rolloff, at high current density and luminance by exciton annihilations in organic light-emitting diodes (OLEDs). Here, we report a deep-blue TADF emitter employing simple molecular design, in which an activation energy as well as spin-orbit coupling between excited states with different spin multiplicities, were simultaneously controlled. An extremely fast exciton lifetime of 750 ns was realized in a donor-acceptor-type molecular structure without heavy metal elements. An OLED utilizing this TADF emitter displayed deep-blue electroluminescence (EL) with CIE chromaticity coordinates of (0.14, 0.18) and a high maximum EL quantum efficiency of 20.7%. Further, the high maximum efficiency were retained to be 20.2% and 17.4% even at high luminance.

Thermally activated delayed fluorescence (TADF) materials, which enable the full harvesting of singlet and triplet excited states for light emission, are expected as the third-generation emitters for organic light-emitting diodes (OLEDs), superseding the conventional fluorescence and phosphorescence materials. High photoluminescence quantum yield (Φ PL ), narrow-band emission (or high color purity), and short delayed fluorescence lifetime are all strongly desired for practical applications. However, to date, no rational design strategy of TADF emitters is established to fulfill these requirements.Here, an epoch-making design strategy is proposed for producing high-performance TADF emitters that concurrently exhibiting high Φ PL values close to 100%, narrow emission bandwidths, and short emission lifetimes of ≈1 µs, with a fast reverse intersystem crossing rate of over 10 6 s −1 . A new family of TADF emitters based on dibenzoheteraborins is introduced, which enable both doped and non-doped TADF-OLEDs to achieve markedly high external electroluminescence quantum efficiencies, exceeding 20%, and negligible efficiency roll-offs at a practical high luminance. Systematic photophysical and theoretical investigations and device evaluations for these dibenzoheteraborin-based TADF emitters are reported here.

Luminescent materials consisting of boron clusters, such as carboranes, have attracted immense interest in recent years. In this study, luminescent organic-inorganic conjugated systems based on o-carboranes directly bonded to electron-donating and electron-accepting π-conjugated units were elaborated as novel optoelectronic materials. These o-carborane derivatives simultaneously possessed aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF) capabilities, and showed strong yellow-to-red emissions with high photoluminescence quantum efficiencies of up to 97 % in their aggregated states or in solid neat films. Organic light-emitting diodes utilizing these o-carborane derivatives as a nondoped emission layer exhibited maximum external electroluminescence quantum efficiencies as high as 11 %, originating from TADF.

To achieve an ultimate wide color gamut for ultrahigh‐definition displays, there is great demand for the development of organic light‐emitting diodes (OLEDs) enabling monochromatic, ultrapure blue electroluminescence (EL). Herein, high‐efficiency and ultrapure blue OLEDs based on polycyclo‐heteraborin multi‐resonance thermally activated delayed fluorescence (MR‐TADF) materials, BOBO‐Z, BOBS‐Z, and BSBS‐Z, are reported. The key to the design of the present luminophores is the exquisite combination and interplay of multiple boron, nitrogen, oxygen, and sulfur heteroatoms embedded in a fused polycyclic π‐system. Comprehensive photophysical and computational investigations of this family of MR‐TADF materials reveal that the systematic implementation of chalcogen (oxygen and sulfur) atoms can finely modulate the emission color while maintaining a narrow bandwidth, as well as the spin‐flipping rates between the excited singlet and triplet states. Consequently, OLEDs based on BOBO‐Z, BOBS‐Z, and BSBS‐Z demonstrate narrowband and ultrapure blue EL emission, with peaks at 445–463 nm and full width at half maxima of 18–23 nm, leading to Commission Internationale de l'Éclairage‐y coordinates in the range of 0.04–0.08. Particularly, for OLEDs incorporating sulfur‐doped BOBS‐Z and BSBS‐Z, notably high maximum external EL quantum efficiencies of 26.9% and 26.8%, respectively, and small efficiency roll‐offs are achieved concurrently.