Enhanced Thermally Activated Delayed Fluorescence by Sole Coordination: From an Organic Molecule to Its Zinc Complex.

A BPAPTPyC organic molecule containing a sandwich structural chromophore is designed and synthesized to produce blue thermally activated delayed fluorescence (TADF). The chromophore is composed of two di(4-tert-butylphenyl)amino donors and one inserted terpyridyl acceptor hitched at positions 1, 8, and 9 of a single carbazole via the p-phenylene group, in which the multiple space π-π interactions between the donor and acceptor enable the molecule to possess the TADF feature with a high energy emission at 470 nm but a low photoluminescence quantum yield (PLQY) and a small proportion of the delayed component. In contrast, the corresponding Zn(BPAPTPyC)Cl2 complex has a high PLQY and a short lifetime with a red-shifted emission due to the enhanced rigidity and electron accepting ability of the terpyridyl group from coordination. A solution-processed organic light-emitting diode (OLED) based on the complex achieves a maximum external quantum efficiency (EQE) of 17.9% with an emission peak at 585 nm, while an OLED of the organic molecule produces blue emission with a maximum EQE of 2.7%.

The Biosynthesis of 1-octene-3-ol by a Multifunctional Fatty Acid Dioxygenase and Hydroperoxide Lyase in Agaricus bisporus.

The biosynthetic pathway from linoleic acid to 1-octen-3-ol in Agaricus bisporus has long been established, in which linoleic acid is converted to 10-hydroperoxide (10-HPOD) by deoxygenation, and 10-HPOD is subsequently cleaved to yield 1-octene-3-ol and 10-oxodecanoic acid. However, the corresponding enzymes have not been identified and cloned. In the present study, four putative genes involved in oxylipid biosynthesis, including one lipoxygenase gene named AbLOX, two linoleate diol synthase genes named AbLDS1 and AbLDS2, and one hydroperoxide lyase gene named AbHPL were retrieved from the A. bisporus genome by a homology search and cloned and expressed prokaryotically. AbLOX, AbLDS1, and AbLDS2 all exhibited fatty acid dioxygenase activity, catalyzing the conversion of linoleic acid to generate hydroperoxide, and AbHPL showed a cleaving hydroperoxide activity, as was determined by the KI-starch method. AbLOX and AbHPL catalyzed linoleic acid to 1-octen-3-ol with an optimum temperature of 35 °C and an optimum pH of 7.2, whereas AbLDS1, AbLDS2, and AbHPL catalyzed linoleic acid without 1-octen-3-ol. Reduced AbLOX expression in antisense AbLOX transformants was correlated with a decrease in the yield of 1-octen-3-ol. AbLOX and AbHPL were highly homologous to the sesquiterpene synthase Cop4 of Coprinus cinerea and the yeast sterol C-22 desaturase, respectively. These results reveal that the enzymes for the oxidative cleavage of linoleic acid to synthesize 1-octen-3-ol in A. bisporus are the multifunctional fatty acid dioxygenase AbLOX and hydroperoxide lyase AbHPL.

Impact of ΔEST on Delayed Fluorescence Rate, Lifetime, and Intensity Ratio of Tetrahedral Cu(I) Complexes: Theoretical Simulation in Solution and Solid Phases.

Profound understanding of the luminescence mechanism and structure-property relationship is vital for Cu(I) thermally activated delayed fluorescence (TADF) emitters. Herein, we theoretically simulated luminescent behavior in both solution and solid phases for two Cu(I) complexes and found the following: (i) The strengthened spin-orbit coupling (SOC) effect by more dx2-y2 orbital contributions and well-restricted structural distortion via remarkable intramolecular interaction in [Cu(dmp)(POP)]+ enable the emission at room temperature to be a mixture of direct phosphorescence (10%) and TADF (90%). (ii) Benefiting from enhanced steric hindrance and the electron-donating ability of the paracyclophane group, the narrowed S1-T1 energy separation (ΔEST) in [Cu(dmp)(phanephos)]+ accelerates the reverse intersystem crossing, promoting the TADF rate (1.88 × 105 s-1) and intensity ratio (98.3%). These results indicate that the small ΔEST is superior for reducing the lifetime and that the strong SOC stimulates the phosphorescence to compete with TADF, which are both conducive to avoiding collision-induced exciton quenching and reducing the roll-off in devices.

Molecular-Level Insight of Cu(I) Complexes with the 7,8-Bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate Ligand as a Thermally Activated Delayed Fluorescence Emitter: Luminescent Mechanism and Design Strategy.

Investigation of the clear structure-property relationship and microscopic mechanism of thermally activated delayed fluorescence (TADF) emitters with high emission quantum yield is a direction worthy of continuous efforts. The instructive theoretical principle of TADF material design is critical and challenging. Here, we carried out theoretical calculation on two experimental Cu(I) complexes with the same 7,8-bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate (dppnc) but different N^N ligands [dmbpy = 6,6'-dimethyl-2,2'-bipyridine (1) or dmp = 2,9-dimethyl-1,10-phenanthroline (2)] to briefly elaborate the structure-TADF performance relationship and luminescence mechanism. It was found that enhanced rigidity by the fused benzene ring between two pyridyl units in complex 2 leads to (i) higher allowedness of S1 → S0, (ii) more effective reverse intersystem crossing (RISC), and (iii) better relative stability of the T1 state, which could be responsible for its excellent TADF behavior. Thus, a strategy of extending π conjugation in the N^N ligand could be deduced to further enhance the quantum yield. We validated it and have succeeded in designing analogue complex 4 by extending π conjugation with an electron-withdrawing pyrazinyl. Benefiting from the smaller energy gap (ΔEST) and plunged reorganization energy between the S1 and T1 states, the rate of RISC in complex 4 (1.05 × 108 s-1) increased 2 orders of magnitude relative to that of 2 (5.80 × 106 s-1), showing more superiority of the TADF behavior through a better balance of RISC, fluorescence, and phosphorescence decay. Meanwhile, the thermally activated temperature of 4 is only 165 K, implying that there is a low-energy barrier. All of these indicate that the designed complex 4 may be a potential TADF candidate.

Saturated Red Electroluminescence From Thermally Activated Delayed Fluorescence Conjugated Polymers.

Two sets of conjugated polymers with anthraquinone groups as pendant acceptors were designed and synthesized. The acceptor is tethered to an diphenylamine group via a phenylene bridge, constructing a thermally activated delayed fluorescence (TADF) unit, which is embedded into the polymer backbone through its donor fragment, while the backbone is composed of dibenzothiophene-S, S-dioxide and 2, 7-fluorene or 2, 7-carbazole groups. The polymers show distinct TADF characteristics, confirmed by transient photoluminescence spectra and theoretical calculations. The carbazole-based polymers exhibit shorter delay lifetimes and lower energy emission relative to the fluorene-based polymers. The non-doped organic light-emitting diodes fabricated via solution processing approach produce efficient red emissions with the wavelengths of 625-646 nm. The carbazole containing polymer with 2% molar content of the TADF unit exhibits the best maximum external quantum efficiency of 13.6% and saturated red electroluminescence with the Commission Internationale de l'Eclairage coordinates of (0.62, 0.37).

Rotation-restricted thermally activated delayed fluorescence compounds for efficient solution-processed OLEDs with EQEs of up to 24.3% and small roll-off.

Two triphenylamine or 4,4'-di(tert-butyl)triphenylamine groups are introduced at the 1,8-positions of 3,6-di(tert-butyl)-9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)carbazole to yield two emitters containing a cofacial donor-acceptor-donor chromophore, which exhibit strong TADF characteristics dominated by through-space charge-transfer. The solution-processed OLEDs achieve maximum external quantum efficiencies of up to 17.4% and 24.3% with small efficiency roll-off rates.

Theoretical study of radiative and nonradiative decay rates for Cu(i) complexes with double heteroleptic ligands.

In this paper, we conducted DFT and TDDFT calculations on three double heteroleptic Cu(i) complexes to understand how different substituents on N^N ligands influence the phosphorescence quantum yield (PLQY). Both radiative and nonradiative decay processes were thoroughly investigated. Factors that determine the rate of radiative process (kr) were considered, including the lowest triplet excited state E(T1), the transition dipole moment MSm,j of the Sm → S0 transition, the spin-coupled matrix element SOC, and the singlet-triplet splitting energies ΔE(Sm-T1). The results indicate that E(T1), MSm,j and SOC increase and ΔE(Sm-T1) decreases upon introducing -Ph and -CH2- groups on the N^N ligands. The net results lead to a gradual increase of kr in the three Cu(i) complexes, from 1 (0.48 × 104 s-1) to 2 (0.64 × 104 s-1) and then to 3 (1.61 × 104 s-1). The rate of nonradiative decay process (knr) was computed by a convolution method. We explored how knr is determined by SOC between T1 and S0 states (T1|SOC|S02), effective energy gap ΔE' and the Huang-Rhys factor (S). We found that T1|SOC|S02 and ΔE' contribute significantly to knr, but S does not determine the order of knr. knr gradually decreases from complex 1 (2.51 × 106 s-1) to 2 (0.32 × 106 s-1) and then to 3 (0.14 × 106 s-1) after introducing -Ph and -CH2- groups on the N^N ligands. The computed PLQYs for the three complexes are 1: 0.0019, 2: 0.0198, and 3: 0.1011. These are quantitatively consistent with the experimental observation (1: 0.0028, 2: 0.0061, and 3: 0.1000).