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An undergraduate organic chemistry laboratory experiment that provides an introduction to the concepts and practices of photoredox catalysis is reported. While undergraduate-level photochemistry experiments typically place emphasis on analytical properties of catalysts rather than synthetic applications, this experiment showcases the power and versatility of photoredox chemistry in modern organic syntheses. A hypothesis-driven approach is utilized as students apply chemical reasoning to formulate hypotheses predicting the relative catalytic activity of Ru(bpy)32+ and Ru(bpm)32+, which differ slightly in ligand structure. Students work collaboratively to obtain conversion data in [2 + 2] cycloadditions catalyzed by Ru(bpy)32+ and Ru(bpm)32+, and use the data to support or refute their hypotheses. The operationally straightforward experimental protocol has been shown to be robust and reproducible, providing unambiguous results that facilitate student interpretation. Furthermore, the experiment trains students in chemical thinking needed for conducting research. [ABSTRACT FROM AUTHOR]

Triphenylamine (TPA) is a well-known hole-transporting material but suffers aggregation-caused emission quenching in the solid state. Tetraphenylethene (TPE), on the other hand, is an archetypal luminogen that shows the phenomenon of aggregation-induced emission (AIE). In this work, TPA is attached to the TPE core as peripheral group to generate new AIE luminogens with enhanced hole-transporting property. The TPA-TPE adducts, named 1-[4′-(diphenylamino)biphenyl-4-yl]-1,2,2-triphenylethene (TPATPE) and 1,2-bis[4′-(diphenylamino)biphenyl-4-yl]-1,2-diphenylethene (2TPATPE) are synthesized in satisfactory yields by Suzuki coupling of 4-(diphenylamino)phenylboronic acid with 1-(4-bromophenyl)-1,2,2-triphenylethene and 1,2-bis(4-bromophenyl)-1,2-diphenylethene, respectively. Whereas the hybrid molecules are practically nonluminescent in the solution state, their aggregates in poor solvents and thin films emit intensely with fluorescence quantum yields up to 100%. Both TPATPE and 2TPATPE are thermally and morphologically stable, showing high thermal-degradation (Tdup to 430 °C) and glass transition (Tg= 119 °C) temperatures. Multilayer electroluminescence (EL) devices are constructed, which emit sky blue and green EL with maximum luminance of 32230 cd/m2and current efficiency up to 13.0 cd/A. The devices without hole-transporting layers (HTL) show performances comparable to or better than those with HTL, presumably because of the high hole mobility of TPATPE and 2TPATPE coupled with the matching of their energy levels with the anode. [ABSTRACT FROM AUTHOR]

A Rh(III)-catalyzedC–H functionalization approach was developedfor the preparation of multisubstituted 3-fluoropyridines from α-fluoro-α,β-unsaturatedoximes and alkynes. Oximes substituted with aryl, heteroaryl, andalkyl β-substituents were effective coupling partners, as weresymmetrical and unsymmetrical alkynes with aryl and alkyl substituents.The first examples of coupling α,β-unsaturated oximeswith terminal alkynes was also demonstrated and proceeded with uniformlyhigh regioselectivity to provide single 3-fluoropyridine regioisomers.Reactions were also conveniently set up in air on the benchtop. [ABSTRACT FROM AUTHOR]

A straightforward and general strategy for the catalytic asymmetric synthesis of β 3 -tryptophans by carboxylic-acid-directed intermolecular C-H amination has been developed. The iron-catalyzed C-H amination of 3-indolepropionic acids with BocNHOMs (Boc, tert -butyloxycarbonyl; OMs, methylsulfonate) in the presence of the base piperidine provides N-Boc-protected β 3 -tryptophans in a single step with high enantiomeric excess (ee) of up to >99%. Mechanistic experiments and density functional theory calculations support a mechanism through carboxylate-directed iron-mediated C(sp 3 )-H nitrene insertion. The method incorporates two key sustainability criteria: the use of iron as an abundant, non-toxic, and environmentally benign metal, along with the achievement of streamlined enantioselective C-H functionalization.

We describe the first total synthesis of the unusual cyclopropane-containing indole alkaloid (-)-rauvomine B via a strategy centered upon intramolecular cyclopropanation of a tetracyclic N -sulfonyltriazole. Preparation of this precursor evolved through two generations of synthesis, with the ultimately successful route involving a palladium-catalyzed stereospecific allylic amination, a cis -selective Pictet-Spengler reaction, and ring-closing metathesis as important bond-forming reactions. The key cyclopropanation step was found to be highly dependent on the structure and conformational strain of the indoloquinolizidine N -sulfonyltriazole precursor, the origins of which are explored computationally through DFT studies. Overall, our synthesis proceeds in 11 total steps and 2.4% yield from commercial materials.

Theoretically, tandem quantum-dot light-emitting diodes (QLEDs) hold great promise for achieving both high efficiency and high stability in display applications. However, in practice, their operational stability remains considerably inferior to that of state-of-the-art devices. In this study, we developed a new tandem structure with optimal electrical and optical performance to simultaneously improve the efficiency and stability of tandem QLEDs. Electrically, upon development of a barrier-free interconnecting layer enabled by an indium-zinc oxide bridging layer and a conductive ZnMgO layer, the driving voltage of the tandem QLEDs is remarkably reduced. Optically, upon development of a top-emitting structure and optimization of the cavity length guided by a theoretical simulation, a maximum light extraction efficiency is achieved. As a result, the red tandem QLEDs exhibit a maximum external quantum efficiency of 49.01% and a T 95 lifetime at 1000 cd/m 2 of >50 000 h, making them one of the most efficient and stable QLEDs ever reported.

Developing new strategies to enable chemo- and regioselective reductions is an important topic in chemical research. Herein, an efficient and regioselective Pd/IPr BIDEA -catalyzed ring-opening hydrodefluorination of gem -difluorocyclopropanes to access terminal fluoroalkenes is developed. The success of this transformation was attributed to the use of 3,3-dimethylallyl Bpin as a novel hydride donor. DFT calculations suggest that a direct 3,4'-hydride transfer via a 9-membered cyclic transition state is more favorable, which combined with the irreversibility of the reaction enables the unusual selectivity for the less thermodynamically stable terminal alkene isomer. This reaction mode is also applicable to a variety of regioselective allylic and propargyl reductions.

The mechanism of the Ru(II)-catalyzed anti-Markovnikov formal hydroalkylation of 1,3-dienes and enynes by hydrazones has been elucidated using density functional theory (DFT) calculations. Our results indicate that the C-C bond formation proceeds through a highly polar outer-sphere transition state (TS) stabilized by the THF solvent, not the ordered inner-sphere TS as originally proposed. The regioselectivity for 1,2-anti-Markovnikov addition is primarily due to the formation of an extensively π-conjugated intermediate after the nucleophilic attack on the 1-position of the diene. The stability of this intermediate means that nucleophilic attack at the 1-position is able to utilize the outer-sphere pathway, while attacks on all other positions of the diene must proceed through more crowded and less-favorable inner-sphere TSs. We show that the electronics of substituents on the hydrazone and the diene have a significant impact on the C-C formation barrier, which rationalizes the limitations on the substrate scope. The preferred coordination sphere around Ru(II) and the rigidity of the reacting substrates lead to a sterically demanding TS geometry, which explains the sensitivity of the reaction to the ligand size.

This study reports the catalytic deracemization of ketones bearing stereocenters in the α-position in a single reaction via deprotonation, followed by enantioselective protonation. The principle of microscopic reversibility, which has previously rendered this strategy elusive, is overcome by a photoredox deprotonation through single electron transfer and subsequent hydrogen atom transfer (HAT). Specifically, the irradiation of racemic pyridylketones in the presence of a single photocatalyst and a tertiary amine provides nonracemic carbonyl compounds with up to 97% enantiomeric excess. The photocatalyst harvests the visible light, induces the redox process, and is responsible for the asymmetric induction, while the amine serves as a single electron donor, HAT reagent, and proton source. This conceptually simple light-driven strategy of coupling a photoredox deprotonation with a stereocontrolled protonation, in conjunction with an enrichment process, serves as a blueprint for other deracemizations of ubiquitous carbonyl compounds.

Mechanisms and regioselectivities in 1,3-dipolar cycloadditions of diazomethane with alkenes have been investigated with density functional theory (DFT) and DLPNO-CCSD(T) computations. The concerted but asynchronous pathway is shown to be favored by at least 6 kcal/mol over the stepwise diradical pathway in all diazomethane-alkene cycloadditions. Frontier molecular orbital calculations indicate a dominant HOMO dipole → LUMO dipolarophile interaction in diazomethane cycloadditions involving electron-deficient alkenes, whereas for electron-rich alkenes, both frontier interactions contribute significantly, and the regioselectivity is governed by frontier coefficients.

Computational studies with ωB97X-D density functional theory of the mechanisms of the steps in Trauner's biomimetic synthesis of preuisolactone A have elaborated and refined mechanisms of several unique processes. An ambimodal transition state has been identified for the cycloaddition between an o- quinone and a hydroxy- o- quinone; this leads to both (5 + 2) (with H shift) and (4 + 2) cycloaddition products, which can in principle interconvert via α-ketol rearrangements. The origins of periselectivity of this ambimodal cycloaddition have been investigated computationally with molecular dynamics simulations and tested further by an experimental study. In the presence of bicarbonate ions, the deprotonated hydroxy- o- quinone leads to only the (5 + 2) cycloaddition adduct. A new mechanism for a benzilic acid rearrangement resulting in ring contraction is proposed.

Zero-dimensional perovskite nanocrystals (NCs) are becoming the most attractive material due to their excellent optical performance and better stability compared with high-dimensional perovskite. However, their application in electroluminescent (EL) emitters for high-quality displays is still limited. In this work, we successfully achieved CsPbBr 3 @Cs 4 PbBr 6 NCs around 13.9 ± 0.2 nm by using the hot-injection method. Additional SnBr 2 was mixed in the PbBr 2 precursor to provide extra Br - ions and reduce the excessive amount of Pb 2+ ions to promote the formation of CsPbBr 3 @Cs 4 PbBr 6 . Time resolution photoluminescence analysis indicated that the green emission of our CsPbBr 3 @Cs 4 PbBr 6 NCs originated from the embedded CsPbBr 3 NCs, which corresponds to our previous research. The Cs 4 PbBr 6 crystals passivated the surface of CsPbBr 3 NCs, resulting in the absence of trions for the high photoluminescence quantum yield. The as-synthesized CsPbBr 3 @Cs 4 PbBr 6 NCs were used to fabricate quantum dot light-emitting diode (QLED) devices with the highest current efficiency of 4.89 cd/A. This is the best performance of the CsPbBr 3 @Cs 4 PbBr 6 -system QLED device, which reveals the great potential of CsPbBr 3 @Cs 4 PbBr 6 NCs and will inspire further study of zero-dimensional perovskite composite NCs for EL emitters.

Here we interrogate the structurally dense (1.64 mcbits/Å 3 ) GABA A receptor antagonist bilobalide, intermediates en route to its synthesis, and related mechanistic questions. 13 C isotope labeling identifies an unexpected bromine migration en route to an α-selective, catalytic asymmetric Reformatsky reaction, ruling out an asymmetric allylation pathway. Experiment and computation converge on the driving forces behind two surprising observations. First, an oxetane acetal persists in concentrated mineral acid (1.5 M DCl in THF- d 8 /D 2 O); its longevity is correlated to destabilizing steric clash between substituents upon ring-opening. Second, a regioselective oxidation of des -hydroxybilobalide is found to rely on lactone acidification through lone-pair delocalization, which leads to extremely rapid intermolecular enolate equilibration. We also establish equivalent effects of (-)-bilobalide and the nonconvulsive sesquiterpene (-)-jiadifenolide on action potential-independent inhibitory currents at GABAergic synapses, using (+)-bilobalide as a negative control. The high information density of bilobalide distinguishes it from other scaffolds and may characterize natural product (NP) space more generally. Therefore, we also include a Python script to quickly (ca. 132 000 molecules/min) calculate information content (Böttcher scores), which may prove helpful to identify important features of NP space.

We report a photoredox-catalyzed α-amino C-H arylation reaction of highly substituted piperidine derivatives with electron-deficient cyano(hetero)arenes. The scope and limitations of the reaction were explored, with piperidines bearing multiple substitution patterns providing the arylated products in good yields and with high diastereoselectivity. To probe the mechanism of the overall transformation, optical and fluorescent spectroscopic methods were used to investigate the reaction. By employing flash-quench transient absorption spectroscopy, we were able to observe electron transfer processes associated with radical formation beyond the initial excited-state Ir(ppy) 3 oxidation. Following the rapid and unselective C-H arylation reaction, a slower epimerization occurs to provide the high diastereomer ratio observed for a majority of the products. Several stereoisomerically pure products were resubjected to the reaction conditions, each of which converged to the experimentally observed diastereomer ratios. The observed distribution of diastereomers corresponds to a thermodynamic ratio of isomers based upon their calculated relative energies using density functional theory (DFT).

The mechanism and stereoselectivity of the BF 3 -catalyzed, enamide-based domino reaction developed by Manolikakes et al. for tetrahydropyran synthesis have been studied using density functional theory calculations. All σ-bond formations were found to proceed through highly ordered cyclic or bicyclic transition states, leading to remarkable levels of diastereoselectivity. The role of the BF 3 catalyst was demonstrated to be essential in both substrate activation and stereocontrol.

The mechanism of the aza-Diels-Alder reaction catalyzed by tetraalkylammonium or trialkylsulfonium salts is explored with density functional theory. Favorable electrostatic interactions between the dienophile and the charged catalyst stabilize the highly polar transition state, leading to lower free energy barriers and higher dipole moments. Endo selectivity is predicted for both uncatalyzed and catalyzed systems. We also computationally evaluate the effects of oriented external electric fields (EEFs) on the same aza-Diels-Alder reaction, demonstrating that very strong EEFs would be needed to achieve the catalytic strength of these cationic catalysts.

A new class of chiral ruthenium catalysts is introduced in which ruthenium is cyclometalated by two 7-methyl-1,7-phenanthrolinium heterocycles, resulting in chelating pyridylidene remote N-heterocyclic carbene ligands (rNHCs). The overall chirality results from a stereogenic metal center featuring either a Λ or Δ absolute configuration. This work features the importance of the relative metal-centered stereochemistry. Only the non- C 2 -symmetric chiral-at-ruthenium complexes display unprecedented catalytic activity for the intramolecular C(sp 3 )-H amidation of 1,4,2-dioxazol-5-ones to provide chiral γ-lactams with up to 99:1 er and catalyst loadings down to 0.005 mol % (up to 11 200 TON), while the C 2 -symmetric diastereomer favors an undesired Curtius-type rearrangement. DFT calculations elucidate the origins of the superior C-H amidation reactivity displayed by the non- C 2 -symmetric catalysts compared to related C 2 -symmetric counterparts.

Quantum-dot light-emitting diodes (QLEDs) with high brightness have potential application in lighting and display. The high brightness is realized at high current density ( J ). However, at high J , the efficiency drops significantly, thereby limiting the achievable brightness. This notorious phenomenon has been known as efficiency roll-off, which is likely caused by the Auger- and/or thermal-induced emission quenching. In this work, we show that the Joule heat generated during device operation significantly affects the roll-off characteristics of QLEDs. To realize ultrabright and efficient QLEDs, the thermal stability of QDs is improved by replacing the conventional oleic acid ligands with 1-dodecanethiol. By further using a substrate with high thermal conductivity, the Joule heat generated at high J is effectively dissipated. Because of the effective thermal management, thermal-induced emission quenching is significantly suppressed, and consequently, the QLEDs exhibit a high external quantum efficiency (EQE) of 16.6%, which is virtually droop-free over a wide range of brightness ( e . g ., EQE = 16.1% @ 10 5 cd/m 2 and 140 mA/cm 2 ). Moreover, due to the reduced efficiency roll-off and enhanced heat dissipation, the demonstrated QLEDs can be operated at a very high J up to 3885 mA/cm 2 , thus enabling the devices to exhibit a record-high brightness of 1.6 × 10 6 cd/m 2 and a lumen density of 500 lm/cm 2 . Our work demonstrates the significance of thermal management for the development of droop-free and ultrabright QLED devices for a wide variety of applications including lighting, transparent display, projection display, outdoor digital signage, and phototherapy.

A formamidinium (FA)-based perovskite is an ideal option for the potential efficient light-emitting diode (LED) in view of its high tolerance factor closer to 1. In this work, FA cation-based perovskite nanocrystals FA 0.8 Cs 0.2 Pb x Br 3 ( x = 1.0, 0.8, 0.7, and 0.6) are fabricated with stoichiometric modification. The adoption of less-lead precursor is confirmed to be a feasible and effective approach in inhibiting nonradiative recombination by diminishing the presence of uncoordinated metallic Pb atoms. Note that the subsequent devices require the optimized lead ratio for an optimum behavior, a clear influence of Pb ratio on a perovskite LED has been established. No surprisingly, the less-lead perovskites exert positive roles on the perovskite LED performance, not only in terms of efficiency but also in stability. With an optimized composition FA 0.8 Cs 0.2 Pb 0.7 Br 3 , the perovskite LED displays the prominent performance with a current efficiency of 28.61 cd A -1 , about 11-fold improvement than the previous best record of pure FA-based perovskite. Additionally, the perovskite device degradation can be mitigated under operating conditions by properly altering precursor stoichiometry, which can be attributed to the hydrogen reaction under moisture-induced ambient. The stoichiometric optimization of the metal Pb in the perovskite is an important strategy on the road to the further development of perovskite LEDs.

The effect of postannealing on the device characteristics is systematically investigated. The external quantum efficiency (EQE) of blue quantum-dot light-emitting diodes (QLEDs) is significantly improved from 5.22 to 9.81% after postannealing. Similar results are obtained in green and red QLEDs, whose EQEs are enhanced from 11.47 and 13.60 to 15.57 and 16.59%, respectively. The annealed devices also exhibit a larger current density. The origin of efficiency improvement is thoroughly investigated. Our finding indicates that postannealing promotes the interfacial reaction of Al and ZnMgO and consequently leads to the metallization of the AlZnMgO contact and the formation of the AlO x interlayer. Because of the metallization of AlZnMgO, the contact resistance is effectively reduced, and thus the electron injection is enhanced. On the other hand, the formation of the AlO x interlayer can effectively suppress the quenching of excitons by the metal electrode. Because of the enhancement of electron injection and suppression of exciton quenching, the annealed blue, green, and red QLEDs exhibit a 1.9-, a 1.3-, and a 1.2-fold efficiency improvement, respectively. We envision the results offer a simple yet effective method to enhance the charge injection and the efficiency of QLED devices, which would promote the practical application of QLEDs.

ZnO nanoparticles (NPs) are widely used as the electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs) owing to their suitable electrical properties. However, because of the well-aligned conduction band levels, electrons in QDs can be spontaneously transferred to adjacent ZnO NPs, leading to severe exciton dissociation, which reduces the proportion of radiative recombination and deteriorates the device efficiency. In this work, Al-doped ZnO NPs are thoroughly investigated as a replacement of ZnO for QLEDs. The energy band structures of Al-doped ZnO are modified by adjusting the concentration of Al dopants. With the increasing Al content, the work function and the conduction band edge of ZnO are gradually raised, and thus the charge transfer at the interface of QDs/ETL is effectively suppressed. Consequently, the green QLEDs with 10% Al-doped ZnO NPs exhibit maximum current efficiency and external quantum efficiency of 59.7 cd/A and 14.1%, which are about 1.8-fold higher than 33.3 cd/A and 7.9% of the devices with undoped ZnO NPs. Our work suggests that Al-doped ZnO NPs can serve as a good electron transport/injection material in QLEDs and other optoelectronic devices.

The origin of enantioselectivity in the asymmetric alkynylation of trihalomethyl ketones catalyzed by octahedral stereogenic-at-ruthenium complexes has been investigated through density functional theory calculations. Computational results support a mechanism involving formation of a ruthenium acetylide, followed by pre-coordination of the trihalomethyl ketone through the carbonyl oxygen and intramolecular attack of the acetylide via a compact four-membered transition state. Differences in computed free energies of activation for the formation of the major and minor propargyl alcohol enantiomers are in good agreement with the experimentally observed levels of asymmetric induction. Analysis of fragment distortion energies shows that disfavored transition states are destabilized due to the more severe distortion and loss of π-conjugation in the coordinated arylketone fragments. Examination of the different substitution patterns in the ketone substrate and the catalyst reveals the key steric factors that control the enantioselectivity. Finally, calculations indicate promising directions for the simplification of the catalyst scaffold while preserving the high levels of enantioselectivity of these alkynylation reactions.

The origins of the enantio- and diastereoselectivities in the Mannich reactions between aldehydes and ketimines catalyzed by chiral vicinal diamines have been determined by density functional theory calculations and distortion-interaction analysis. Computational results indicate a strong energetic preference for hydrogen-bonded nine-membered cyclic transition states. The favored transition states involve eight heavy atoms in the crown (chair-chair) conformation using the nomenclature of the analogous cyclic hydrocarbons. Energetic discrimination in the chirality-imparting step arises from pseudogauche-butane-type interactions in the disfavored transition states, as well as steric clashes between the N-Boc protecting group and the ammonium N-substituents.