Search

Narrowband emitters possess great potential in organic light emitting diodes (OLEDs) to achieve high color purity. However, developing highly efficient pure blue emitters with a simultaneously narrow full width at half-maximum (FWHM) value is a major challenge due to the energy-gap law and molecular stacking effect. Few efforts have focused on this challenging pursuit. Herein, an ingenious synthetic method was devised to achieve pure blue emitters incorporating bulky rigid planes as donors and highly twisted steric units as acceptors. Four emitters with aggregation-induced emission (AIE) characteristics, namely BCzPPM, BC-zPSP, IDCz-DBPM, and IDCz-BPSP, have been developed and used to fabricate non-doped devices. IDCz-BPSP achieves narrowed photoluminescence (PL) and electroluminescence (EL) with the benefit of suppressing vibronic coupling. Non-doped OLEDs based on IDCz-BPSP have achieved maximum external quantum efficiency (EQE max) of 4.61% with a FWHM of 25 nm/0.20 eV. The Commission Internationale de L'Eclairage (CIE) coordinates was (0.154, 0.059), with CIE y being superior to the standard of European Broadcasting Union (EBU) 0.06. The hybridized local and charge-transfer (HLCT) states of IDCz-BPSP have simultaneously boosted the PL efficiency and exciton utilization. The EL process has even achieved exciton utilization at exceeding the theoretical limit of 25%. These results indicate that the strategy of combining bulky rigid plane donor units and steric hindrance effect is a favorable strategy for constructing emitters with narrow FWHM. [Display omitted] • A "single bond-linked" strategy for deep blue AIE emitters was proposed. • The HLCT states of IDCz-BPSP have simultaneously boosted the PL efficiency and exciton utilization. • IDCz-BPSP exhibits a narrow PL and EL FWHM of 24 nm (0.19 eV) and 25 nm (0.20 eV), respectively. • Non-doped OLEDs based on IDCz-BPSP provided ultrapure deep blue emission with CIE y ＜0.06. [ABSTRACT FROM AUTHOR]

Three aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF) blue light-emitting materials were successfully synthesized using bicarbazole and phenylsulfonyl/benzophenone moieties as electron donors and acceptors, respectively, via Buchwald-Hartwig reaction. Density functional theory calculations showed that the three emitters have a moderate dihedral angle between the two carbazole planes and between the donor and acceptor, resulting in a good conjugated structure and a trade-off between the small Δ E ST and high photoluminescence quantum yield of the BCzDPM molecule. The cyclic voltammetry, thermogravimetric analysis and differential scanning calorimetry tests demonstrated that the three materials had high electrochemical and thermal stability. The three emitters exhibited obvious intramolecular charge transfer characteristics in solution and film. According to the fluorescence and low-temperature phosphorescence spectra, the lowest singlet and triplet excited state energy levels of BCzDPM were 2.96 eV and 2.78 eV, respectively, with a Δ E ST of 0.18 eV. Using these emitters as non-doped emissive layers, efficient blue electroluminescent devices were fabricated. The maximum current efficiency and external quantum efficiency reached 15.4 cd/A and 7.05% for the BCzDPM device, respectively, and the efficiency roll-off of BCzDPM was smaller than that of PSOBCz and PBCzPM, under high current density. [Display omitted] • The twisted molecule has a moderate dihedral angle, resulting in a trade-off between small Δ E ST and high Φ PL. • BCzDPM simultaneous combination of AIE and TADF properties. • BCzDPM exhibit small Δ E ST of 0.18 eV and high Φ PL of 67%. • BCzDPM film has high k ISC , k RISC , and k F values implying rapid decay of T 1.→S 1 and S 1 →S 0 for emission. [ABSTRACT FROM AUTHOR]

Abstract Currently, aggregation-induced delayed fluorescence (AIDF) is the most potential method that overcomes the limitations of thermally activated delayed fluorescence (TADF) emitters. Herein, to develop high efficient AIDF emitters, a novel strategy of introducing carbazole dendrites to a strengthen electron acceptor to construct D−π−A structure has been presented. Two emitters, namely diphenyl(4-(4-phenyl-6-(4-(3,3″,6,6″-tetra- tert -butyl-9′H-[9,3':6′,9″-tercarbazol]-9′-yl)phen yl)-1,3,5-triazin-2-yl)phenyl) phosphine oxide (CzTAZPO) and diphenyl(4-(4-phenyl-6-(4-(3,3″,6,6″-tetra- tert -butyl-9′H-[9,3':6′,9″-tercarbazol]-9′-yl)phenyl)-1,3,5-triazin-2-yl)phenyl)phosphine oxide (sCzTAZPO) with a twisted carbazole dendrites structure are synthesized and investigated theoretically and experimentally. Both compounds show aggregation-induced emission, a prominent TADF and bipolar properties. The reasonable molecular design strategy allows CzTAZPO to exhibit high oscillator strengths (f) and small singlet–triplet energy gap (Δ E ST) at the same time, which signifcantly increase the rate of reverse intersystem crossing process and fluorescence quantum efficiency. High-performance nondoped OLEDs are fabricated with CzTAZPO neat films as the emission layers, providing excellent maximum current efficiency (CE max) and maximum external quantum efficiency (EQE max) of 29.1 cd A−1 and 12.8%, respectively. More importantly, nondoped OLEDs provided negligible EQE roll-off of 1.6% from the maximum values to those at 1000 cd m−2. The AIDF emitters with small Δ E ST , high photoluminescence quantum yields (Φ PL), bipolar charge transport and high rate constant of reverse intersystem crossing process are promising candidates for OLEDs that are roll-off-free and possess high efficiency. Graphical abstract Image 1 Highlights • A strategy to construct solution-processed AIDF was proposed. • Two solution-processed AIDF emitters were designed and synthesized. • CzTAZPO exhibit high oscillator strengths and small singlet–triplet energy gap. • CzTAZPO based nondoped OLED shown high efficiencies (EQE>12%) and low roll-off (<1.6%). • This strategy would be a promising method for efficient and stable OLEDs. [ABSTRACT FROM AUTHOR]

Due to the limited molecular design strategy, the development of ultrahigh color purity deep blue aggregation-induced emission (AIE) emitters with excellent photophysical and electroluminescence performances is still facing challenges at present. In this study, an effective design strategy for deep blue emitters is proposed, which can improve the performances of non-doped organic light-emitting diodes (OLEDs) by adjusting the link mode of the phenyl bridge and utilizing the steric hindrance effect of the rigid plane. Two new emitters, 3BCzPT and 4BCzPT, were obtained with phenanthroline acceptor and carbazole donor for deep blue emitting OLEDs. Particularly, 3BCzPT has been proven to have AIE characteristics through photophysical properties. Non-doped OLEDs with 3BCzPT demonstrate prominent electroluminescence (EL) performances reaching a maximum current efficiency (CEmax) of 6.3 cd A−1 and maximum external quantum efficiency (EQEmax) of 3.81%, well as ultrahigh color purity with Commission Internationale de L'Eclairage (CIE) coordinates of (0.151, 0.053). While the parameters of non-doped OLED based 4BCzPT are 4.2 cd A−1, 1.96% and (0.147, 0.082). Both emitters exhibit narrow EL spectra with the full-width at half maximum (FWHM) of 56 and 52 nm. • A strategy to construct deep blue AIE emitters with D-π-A-π-D configuration was proposed. • Highly twisted configurations are beneficial to the formation of weak intra/intermolecular interaction. • Non-doped OLEDs provided ultrapure deep blue emission with CIE x ≤0.15 and CIE y ≤0.08. • This feasible strategy can enrich the design strategy of deep blue emitters and further extend their application in OLEDs. [ABSTRACT FROM AUTHOR]