Controlling crystal growth and reducing the number of grain boundaries are crucial to maximize the charge carrier transport in organic–inorganic perovskite field-effect transistors (FETs). Herein, the crystallization and growth kinetics of a Sn(II)-based 2D perovskite, using 2-thiopheneethylammonium (TEA) as the organic cation spacer, were effectively regulated by the hot-casting method. With increasing crystalline grain size, the local charge carrier mobility is found to increase moderately from 13 cm2 V−1 s−1 to 16 cm2 V−1 s−1, as inferred from terahertz (THz) spectroscopy. In contrast, the FET operation parameters, including mobility, threshold voltage, hysteresis, and subthreshold swing, improve substantially with larger grain size. The optimized 2D (TEA)2SnI4 transistor exhibits hole mobility of up to 0.34 cm2 V−1 s−1 at 295 K and a higher value of 1.8 cm2 V−1 s−1 at 100 K. Our work provides an important insight into the grain engineering of 2D perovskites for high-performance FETs.

The performance of perovskite solar cells with inverted polarity (p-i-n) is still limited by recombination at their electron extraction interface, which also lowers the power conversion efficiency (PCE) of p-i-n perovskite-silicon tandem solar cells. A MgFx interlayer with thickness of ~1 nanometer at the perovskite/C60 interface favorably adjusts the surface energy of the perovskite layer through thermal evaporation, which facilitates efficient electron extraction and displaces C60 from the perovskite surface to mitigate nonradiative recombination. These effects enable a champion open-circuit voltage of 1.92 volts, an improved fill factor of 80.7%, and an independently certified stabilized PCE of 29.3% for a monolithic perovskite-silicon tandem solar cell ~1 square centimeter in area. The tandem retained ~95% of its initial performance after damp-heat testing (85°C at 85% relative humidity) for >1000 hours.

All-inorganic metal halide perovskite nanocrystals (NCs) having the general formula ABX3, where A is a monovalent cation, for example, Cs+, B is a divalent cation, typically Pb2+, and X is Cl–, Br–, I–, or their binary mixture, show potential in optoelectronic devices. In this work, we explore the effect of B-site doping on the optoelectronic properties of CsPbX3 NCs (X = Br, Cl). First, the Pb2+ ions in the pristine CsPbBr3 NC are partially substituted by Mn2+ ions. The alkaline earth metal strontium is then doped on both pristine and the Mn2+-substituted NCs. We found that a small percentage of Sr2+ doping remarkably improves the photoluminescence quantum yield of CsPbBr3 and Mn2+-state emission in Mn2+:CsPb(Br,Cl)3 NCs. Perovskite NC film/poly(methyl methacrylate) composites with all four NC variants were used in a white light-emitting diode (WLED), where Sr2+ doping increased the luminous efficiency of the WLED by ∼4.7%. We attribute this performance enhancement to a reduced defect density and an attenuated microstrain in the local NC structure.

Surface-defect passivation is key to achieving a high photoluminescence quantum yield in lead halide perovskite nanocrystals. However, in perovskite light-emitting diodes, these surface ligands also have to enable balanced charge injection into the nanocrystals to yield high efficiency and operational lifetime. In this respect, alkaline halides have been reported to passivate surface trap states and increase the overall stability of perovskite light emitters. On the one side, the incorporation of alkaline ions into the lead halide perovskite crystal structure is considered to counterbalance cation vacancies, whereas on the other side, the excess halides are believed to stabilize the colloids. Here, we report an organic lithium salt, viz. LiTFSI, as a halide-free surface passivation on perovskite nanocrystals. We show that treatment with LiTFSI has multiple beneficial effects on lead halide perovskite nanocrystals and LEDs derived from them. We obtain a higher photoluminescence quantum yield and a longer exciton lifetime and a radiation pattern that is more favorable for light outcoupling. The ligand-induced dipoles on the nanocrystal surface shift their energy levels toward a lower hole-injection barrier. Overall, these effects add up to a 4- to 7-fold boost of the external quantum efficiency in proof-of-concept LED structures, depending on the color of the used lead halide perovskite nanocrystal emitters.

Temperature can affect many biological and chemical processes within a body. During in vivo measurements, varied temperature can impact the accurate quantification of additional abiotic factors such as oxygen. During magnetic resonance imaging (MRI) measurements, the temperature of the sample can increase with the absorption of radiofrequency energy, which needs to be well-regulated for thermal therapies and long exposure. To address this potentially confounding effect, temperature can be probed intentionally using reporter molecules to determine the temperature in vivo. This work describes a combined experimental and computational approach for the design of fluorinated molecular temperature sensors with the potential to improve the accuracy and sensitivity of 19F MRI-based temperature monitoring. These fluorinated sensors are being developed to overcome the temperature sensitivity and tissue limitations of the proton resonance frequency (10 × 10–3 ppm °C–1), a standard parameter used for temperature mapping in MRI. Here, we develop (perfluoro-[1,1′-biphenyl]-4,4′-diyl)bis((heptadecafluorodecyl)sulfane), which has a nearly 2-fold increase in temperature responsiveness, compared to the proton resonance frequency and the 19F MRI temperature sensor perfluorotributylamine, when tested under identical NMR conditions. While 19F MRI is in the early stages of translation into clinical practice, development of alternative sensors with improved diagnostic abilities will help advance the development and incorporation of fluorine magnetic resonance techniques for clinical use.

Combining strong light absorption and outstanding electrical conductivity, hybrid nanographene–graphene (NG–Gr) van der Waals heterostructures (vdWHs) represent an emerging material platform for versatile optoelectronic devices. Interfacial charge transfer (CT), a fundamental process whose full control remains limited, plays a paramount role in determining the final device performance. Here, we demonstrate that the interlayer vdW interactions can be engineered by tuning the sizes of bottom-up synthesized NGs to control the interfacial electronic coupling strength and, thus, the CT process in NG–Gr vdWHs. By increasing the dimensions of NGs from 42 to 96 sp2 carbon atoms in the polyaromatic core to enhance the interfacial coupling strength, we find that the CT efficiency and rate in NG–Gr vdWHs display a drastic increase of one order of magnitude, despite the fact that the interfacial energy driving the CT process is unfavorably reduced. Our results shed light on the CT mechanism and provide an effective knob to tune the electronic coupling at NG–Gr interfaces by controlling the size-dependent vdW interactions.

We correlate spatially resolved fluorescence (-lifetime) measurements with X-ray nanodiffraction to reveal surface defects in supercrystals of self-assembled cesium lead halide perovskite nanocrystals and study their effect on the fluorescence properties. Upon comparison with density functional modeling, we show that a loss in structural coherence, an increasing atomic misalignment between adjacent nanocrystals, and growing compressive strain near the surface of the supercrystal are responsible for the observed fluorescence blueshift and decreased fluorescence lifetimes. Such surface defect-related optical properties extend the frequently assumed analogy between atoms and nanocrystals as so-called quasi-atoms. Our results emphasize the importance of minimizing strain during the self-assembly of perovskite nanocrystals into supercrystals for lighting application such as superfluorescent emitters.

Surface ligand exchange on all-inorganic perovskite nanocrystals of composition CsPbBrI2 reveals improved optoelectronic properties due to strong interactions of the nanocrystal with mono-functionalized porphyrin derivatives. The interaction is verified experimentally with an array of spectroscopic measurements as well as computationally by exploiting density functional theory calculations. The enhanced current efficiency is attributed to a lowering of the charging energy by a factor of 2–3, which is determined by combining electronic and optical measurements on a selection of ligands. The coupled organic–inorganic nanostructures are successfully deployed in a light-emitting device with higher current efficacy and improved charge carrier balance, magnifying the efficiency almost fivefold compared to the native ligand.

Single-site catalysts with active species anchored over metal–organic framework (MOF) supports have garnered significant interest in recent years. Catalysts with vanadium oxide (VOx) species immobilized over Zr-NU-1000 and Hf-MOF-808 (which have nodes containing six Zr(IV) or Hf(IV) ions, respectively) were recently characterized experimentally (Otake et al. J. Am. Chem. Soc.2018,140, 8652) and were reported to be active for the selective oxidation of benzyl alcohol to benzaldehyde. Here, we report a detailed computational investigation of these VOx-incorporated MOF catalysts (V-MOF) by employing density functional theory. Based on the mode of VOx attachment, various structures are explored, and their relative stabilities and computed IR spectral features are reported. Mechanisms for the selective oxidation reaction are investigated. The analysis of electron flow in the turnover-limiting C–H activation step shows that the hydrogen-atom abstraction process involves a concerted proton-coupled electron-transfer mechanism. The results of this study suggest that in addition to the identity of the metal in the node, the MOF node architecture plays a crucial role in driving the catalytic activities of V-MOFs.

Site selectivity represents a key challenge for non-directed C–H functionalization, even when the C–H bond is intrinsically reactive. Here, we report a copper-catalyzed method for benzylic C–H azidation of diverse molecules. Experimental and density functional theory studies suggest the benzyl radical reacts with a CuII-azide species via a radical-polar crossover pathway. Comparison of this method with other C–H azidation methods highlights its unique site selectivity, and conversions of the benzyl azide products into amine, triazole, tetrazole, and pyrrole functional groups highlight the broad utility of this method for target molecule synthesis and medicinal chemistry.

Cross-coupling reactions enable rapid, convergent synthesis of diverse molecules and provide the foundation for modern chemical synthesis. The most widely used methods employ sp2-hybridized coupling partners, such as aryl halides or related pre-functionalized substrates. Here, we demonstrate copper-catalysed oxidative cross-coupling of benzylic C–H bonds with alcohols to afford benzyl ethers, enabled by a redox buffering strategy that maintains the activity of the copper catalyst throughout the reaction. The reactions employ the C–H substrate as the limiting reagent and exhibit broad scope with respect to both coupling partners. This approach to direct site-selective functionalization of C(sp3)–H bonds provides the basis for efficient three-dimensional diversification of organic molecules and should find widespread utility in organic synthesis, particularly for medicinal chemistry applications.

The solid state and fluxional behaviors in solution of complexes L2AlOBn and L7AlOBn (Bn = benzyl) supported by an analog of salen incorporating indolide arms connected via their 2- and 7-positions were defined by experiment and theory. The complexes catalyze the stereoselective conversion of rac-lactide (rac-LA) to isotactically enriched polylactide. A key aspect of the stereocontrol was examined through study of the initiation reactions via NMR spectroscopy, X-ray crystal structures of the ring-opened products, and theory. The results include the first unambiguous structural definition of stereocontrol in ring-opening of LA by a metal–alkoxide complex and the finding that definition of the stereochemistry of initiation by the studied system is governed thermodynamically rather than kinetically.

A series of complexes {[NBu4][LCuII(O2CR)] (R = −C6F5, −C6H4(NO2), −C6H5, −C6H4(OMe), −CH3, and −C6H2(iPr)3)} were characterized (with the complex R = −C6H4(m-Cl) having been published elsewhere (Mandal et al. J. Am. Chem. Soc. 2019, 141, 17236)). All feature N,N′,N″-coordination of the supporting L2– ligand, except for the complex with R = −C6H2(iPr)3, which exhibits N,N′,O-coordination. For the N,N′,N″-bound complexes, redox properties, UV–vis ligand-to-metal charge transfer (LMCT) features, and rates of hydrogen atom abstraction from 2,4,6,-tri-t-butylphenol using the oxidized, formally Cu(III) compounds LCuIII(O2CR) correlated well with the electron donating nature of R as measured both experimentally and computationally. Specifically, the greater the electron donation, the lower is the energy for LMCT and the slower is the reaction rate. The results are interpreted to support an oxidatively asynchronous proton-coupled electron transfer mechanism that is sensitive to the oxidative power of the [CuIII(O2CR)]2+ core.

In a possibly biomimetic fashion, formally copper(III)–oxygen complexes LCu(III)–OH (1) and LCu(III)–OOCm (2) (L2– = N,N′-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide, Cm = α,α-dimethylbenzyl) have been shown to activate X–H bonds (X = C, O). Herein, we demonstrate similar X–H bond activation by a formally Cu(III) complex supported by the same dicarboxamido ligand, LCu(III)–O2CAr1 (3, Ar1 = meta-chlorophenyl), and we compare its reactivity to that of 1 and 2. Kinetic measurements revealed a second order reaction with distinct differences in the rates: 1 reacts the fastest in the presence of O–H or C–H based substrates, followed by 3, which is followed by (unreactive) 2. The difference in reactivity is attributed to both a varying oxidizing ability of the studied complexes and to a variation in X–H bond functionalization mechanisms, which in these cases are characterized as either a hydrogen-atom transfer (HAT) or a concerted proton-coupled electron transfer (cPCET). Select theoretical tools have been employed to distinguish these two cases, both of which generally focus on whether the electron (e–) and proton (H+) travel “together” as a true H atom, (HAT), or whether the H+ and e– are transferred in concert, but travel between different donor/acceptor centers (cPCET). In this work, we reveal that both mechanisms are active for X–H bond activation by 1–3, with interesting variations as a function of substrate and copper functionality.

Single-site heterogeneous catalysts (SSHCs) play important roles in fundamental science and technology, owing to the molecular level control of structure–support interactions that is possible in these systems. Recently, SSHCs supported by acidic oxides have attracted particular interest because catalytically active metal centers can be formed at the surface sites. Here, we incorporated a palladium SSHC in phosphated and sulfated metal–organic frameworks (MOFs), hafnium-based MOF-808 (Hf-MOF-808-PO4 and Hf-MOF-808-SO4). The structural and electronic properties of the Pd(II) sites coordinated to the acidic sites in these MOFs were investigated through X-ray photoelectron spectroscopy, vibrational spectroscopy, X-ray crystallographic techniques, catalytic studies, and quantum mechanical electronic structure calculations employing density functional theory. We demonstrated that the presence of node-bound acidic functional groups stabilizes the Pd(II) site in these MOFs, resulting in enhanced catalytic activities (compared to in the nonacid functionalized Hf-MOF-808) in the oxidative Heck reaction where Pd(II) is the active species. The density functional calculations support the interpretation that the acid functionalization of the MOF node can stabilize the Pd(0) intermediate state during the catalytic reactions, thereby suppressing Pd(0) aggregation leading to catalyst deactivation. These findings offer insights and methodology for the catalytic investigation of SSHCs in MOFs.

Isosorbide is a rigid, sugar-derived building block that has shown promise in high-performance materials, albeit with a lack of available controlled polymerization methods. To this end, we provide mechanistic insights into the cationic and quasi-zwitterionic ring-opening polymerization (ROP) of an annulated isosorbide derivative (1,4:2,5:3,6-trianhydro-d-mannitol, 5). Ring-opening selectivity of this tricyclic ether was achieved, and the polymerization is selectively directed toward different macromolecular architectures, allowing for formation of either linear or cyclic polymers. Notably, straightforward recycling of unreacted monomer can be accomplished via sublimation. This work provides the first platform for tailored polymer architectures from isosorbide via ROP.

Computational screening of a series of aluminum complexes for their activity in the ring-opening transesterification polymerization (ROTEP) of ε-caprolactone (CL) was performed using a “framework distortion energy” (FDE) hypothesis. An {N,N,N,N}-aluminum complex with a bis-indolide Schiff-base ligand was predicted on the basis of that screening to be an efficient catalyst, and this prediction was tested and verified experimentally through the synthesis and characterization of the complex and evaluation of its ROTEP reactivity.

Aluminum alkoxide complexes supported by salen ligands [salen = N,N′-bis(salicylaldimine)-2-methylpropane-1,2-diamine or N,N′-bis(salicylaldimine)-2,2-dimethylpropane-1,3-diamine] with o-adamantyl substituents have been synthesized and investigated for the polymerization of ε-caprolactone. Geometric analysis of the catalysts used for the reaction reveals the metal coordination geometries to be intermediate between square-pyramidal and trigonal-bipyramidal. A detailed kinetic study accompanied by density functional theory modeling of key mechanistic steps of the reaction suggest that, in addition to the length of the backbone linker, the o-aryl substituents have a significant impact on the catalyst’s reactivity. Bulky ortho substituents favorably distort the precatalyst geometry and thereby foster the achievement of the rate-limiting transition-state geometry at low energetic cost, thus accelerating the reaction.

The ring-opening transesterification polymerization (ROTEP) of rac-lactide (rac-LA) using LXZn catalysts (LX = ligand having phenolate, amine, and pyridine donors with variable para substituents X on the bound phenolate donor; X = NO2, Br, t-Bu, OMe) was evaluated through kinetics experiments and density functional theory, with the aim of determining how electronic modulation of the ligand framework influences polymerization rate, selectivity, and control. After determination that zinc-ethyl precatalysts required 24 h of reaction with benzyl alcohol to convert to active alkoxide complexes, the subsequently formed species proved to be active and fairly selective, polymerizing up to 300 equiv of rac-LA in 6–10 min while yielding isotactic (Pm = 0.72–0.78) polylactide (PLA) with low dispersities: Đ = 1.06–1.17. In contrast to previous work with aluminum catalysts for which electronic effects of ligand substituents were significant (Hammett ρ = +1.2–1.4), the LXZn systems exhibited much less of an effect (ρ = +0.3). Density functional calculations revealed details of the initiation and propagation steps, enabling insights into the high isotacticity and the insensitivity of the rate on the identity of X.

Mechanistic studies involving synergistic experiment and theory were performed on the perfectly alternating copolymerization of 1-butene oxide and carbic anhydride using a (salph)AlCl/[PPN]Cl catalytic pair. These studies showed a first-order dependence of the polymerization rate on the epoxide, a zero-order dependence on the cyclic anhydride, and a first-order dependence on the catalyst only if the two members of the catalytic pair are treated as a single unit. Studies of model complexes showed that a mixed alkoxide/carboxylate aluminum intermediate preferentially opens cyclic anhydride over epoxide. In addition, ring-opening of epoxide by an intermediate comprising multiple carboxylates was found to be rate-determining. On the basis of the experimental results and analysis by DFT calculations, a mechanism involving two catalytic cycles is proposed wherein the alternating copolymerization proceeds via intermediates that have carboxylate ligation in common, and a secondary cycle involving a bis-alkoxide species is avoided, thus explaining the lack of side reactions until the polymerization is complete.

Polymerization of ε-caprolactone (CL) using an aluminum alkoxide catalyst (1) designed to prevent unproductive trans binding was monitored at 110 °C in toluene-d8 by 1H NMR and the concentration versus time data fit to a first-order rate expression. A comparison of t1/2 for 1 to values for many other aluminum alkyl and alkoxide complexes shows much lower activity of 1 toward polymerization of CL. Density functional theory calculations were used to understand the basis for the slow kinetics. The optimized geometry of the ligand framework of 1 was found indeed to make CL trans binding difficult: no trans-bound intermediate could be identified as a local minimum. Nor were local minima for cis-bound precomplexes found, suggesting a concerted coordination–insertion for polymer initiation and propagation. The sluggish performance of 1 is attributed to a high-framework distortion energy required to deform the “resting” ligand geometry to that providing optimal catalysis in the corresponding transition-state structure geometry, thus suggesting a need to incorporate ligand flexibility in the design of efficient polymerization catalysts.

Melanin is the pigment found in human skin that is responsible for both photoprotection and photodamage. Recently there have been reports that greater photodamage of DNA occurs when cells containing melanin are irradiated with ultraviolet (UV) radiation, thus suggesting that the photoproducts of melanin cause DNA damage. Photoionization processes have also been implicated in the photodegradation of melanin. However, not much is known about the oxidation potential of melanin and its monomers. In this work we calculate the ionization energies of monomers, dimers, and few oligomers of eumelanin to estimate the threshold energy required for the ionization of eumelanin. We find that this threshold is within the UV-B region for eumelanin. We also look at the charge and spin distributions of the various ionized states of the monomers that are formed to understand which of the ionization channels might favor monomerization from a covalent dimer.