Recent Submissions

  • Chemoselective Hydrogenation of Alkynes to (Z)-Alkenes Using an Air-Stable Base Metal Catalyst

    Zubar, Viktoriia; Sklyaruk, Jan; Brzozowska, Aleksandra; Rueping, Magnus (Organic Letters, American Chemical Society (ACS), 2020-07-08) [Article]
    A highly selective hydrogenation of alkynes using an air-stable and readily available manganese catalyst has been achieved. The reaction proceeds under mild reaction conditions and tolerates various functional groups, resulting in (Z)-alkenes and allylic alcohols in high yields. Mechanistic experiments suggest that the reaction proceeds via a bifunctional activation involving metal–ligand cooperativity.
  • Unrealistic energy and materials requirement for direct air capture in deep mitigation pathways

    Chatterjee, Sudipta; Huang, Kuo-Wei (Nature Communications, Springer Science and Business Media LLC, 2020-07-03) [Article]
    The increasing global atmospheric CO2 concentration due to heavy reliance on fossil fuels as the primary energy sources (~410 ppm in 2019)1 has made direct extraction or removal of CO2 from ambient air (direct air carbon capture (DACC)) the most logical alternative over traditional modes of carbon capture from large stationary sources because of many of the perceived advantages and compelling arguments2. With the current level of CO2 emissions (32.6 gigatons (Gt)-CO2/year2017)1, Realmonte and co-workers recently imposed the global capacity at 30 Gt-CO2/year as a case study for DACC, and concluded that “in theory DACCS can be an enabling factor for the Paris Agreement objectives” and recommended the policy makers to “support an acceleration in development and deployment of DACCS”3. While challenges of large-scale CO2 utilization and sequestration were recognized and these approaches were deemed impractical4,5, our analysis further showed that the energy and materials requirements for DACC are unrealistic even when the most promising technologies are employed. Thus, DACC is unfortunately only an energetically and financially costly distraction in effective mitigation of climate changes at a meaningful scale before we achieve the status of a significant surplus of carbon-neutral/low-carbon energy.
  • Evidence for Silica Surface Three- and Five-Membered Metallacycle Intermediates in the Catalytic Cycle of Hydroaminoalkylation of Olefins Using Single-Ti-Metal Catalysts

    Yaacoub, Layal F.; Aljuhani, Maha A.; Jedidi, Abdesslem; Al-Harbi, Manal S.; Almaksoud, Walid; Wackerow, Wiebke; Abou-Hamad, Edy; Pelletier, Jeremie; El Eter, Mohamad; Cavallo, Luigi; Basset, Jean-Marie (Organometallics, American Chemical Society (ACS), 2020-06-30) [Article]
    The single-site silica-supported group IV metal amido complex [Ti(NMe2)4] gives the tris(amido)-supported fragment [(=Si−O−)Ti(−NMe2)3], which transforms into a three-membered metallacycle (called a metallaaziridine) by an αH transfer between two amido ligands. When the three-membered metallacycle reacts with 1-octene, it gives a five-membered metallacycle by insertion of the double bond into the M−C bond of the metallaziridine. These two metallacycles, key intermediates in the catalytic cycle of the hydroaminoalkylation of terminal olefins, were isolated and fully characterized following the surface organometallic chemistry (SOMC) concept and procedures. This paper shows that surface organometallic chemistry can be used to identify and fully characterize three- and five-membered metallacycles of Ti in the hydroaminoalkylation of olefins.
  • All-Polycarbonate Thermoplastic Elastomers Based on Triblock Copolymers Derived from Triethylborane-Mediated Sequential Copolymerization of CO2 with Various Epoxides

    Jia, Mingchen; Zhang, Dongyue; de Kort, Gijs W.; Wilsens, Carolus H. R. M.; Rastogi, Sanjay; Hadjichristidis, Nikos; Gnanou, Yves; Feng, Xiaoshuang (Macromolecules, American Chemical Society (ACS), 2020-06-29) [Article]
    Various oxirane monomers including alkyl ether or allyl-substituted ones such as 1-butene oxide, 1-hexene oxide, 1-octene oxide, butyl glycidyl ether, allyl glycidyl ether, and 2-ethylhexyl glycidyl ether were anionically copolymerized with CO2 into polycarbonates using onium salts as initiator in the presence of triethylborane. All copolymerizations exhibited a “living” character, and the monomer consumption was monitored by in situ Fourier-transform infrared spectroscopy. The various polycarbonate samples obtained were characterized by 1H NMR, GPC, and differential scanning calorimetry. In a second step, all-polycarbonate triblock copolymers demonstrating elastomeric behavior were obtained in one pot by sequential copolymerization of CO2 with two different epoxides, using a difunctional initiator. 1-Octene oxide was first copolymerized with CO2 to form the central soft poly(octene carbonate) block which was flanked by two external rigid poly(cyclohexene carbonate) blocks obtained through subsequent copolymerization of cyclohexene oxide with CO2. Upon varying the ratio of 1-octene oxide to cyclohexene oxide and their respective ratios to the initiator, three all-polycarbonate triblock samples were prepared with molar masses of about 350 kg/mol and 22, 26, and 29 mol % hard block content, respectively. The resulting triblock copolymers were analyzed using 1H NMR, GPC, thermogravimetric analysis, differential scanning calorimetry, and atomic force microscopy. All three samples demonstrated typical elastomeric behavior characterized by a high elongation at break and ultimate tensile strength in the same range as those of other natural and synthetic rubbers, in particular those used in applications such as tissue engineering.
  • Facile Green Synthesis of New Copper-Based Metal–Organic Frameworks: Experimental and Theoretical Study of the CO2 Fixation Reaction

    Kurisingal, Jintu Francis; Rachuri, Yadagiri; Gu, Yunjang; Chitumalla, Ramesh Kumar; Vuppala, Srimai; Jang, Joonkyung; Bisht, Kamal Kumar; Suresh, Eringathodi; Park, Dae-Won (ACS Sustainable Chemistry & Engineering, American Chemical Society (ACS), 2020-06-29) [Article]
    Two new entangled Cu(II)-based metal–organic frameworks (MOFs) have been synthesized, namely [Cu(BDC)(BPDB)0.5]n (PNU-25) and [Cu(NH2-BDC)(BPDB)0.5]n (PNU-25-NH2), using a H2O-MeOH solvent mixture. Both the PNU-25 and PNU-25-NH2 MOF materials were characterized by various analytical techniques and their catalytic potential of CO2 fixation into cyclic carbonates at an atmospheric pressure, a low reaction temperature, and in the neat conditions were demonstrated. The amine-functionalized PNU-25-NH2 exhibited a significant high conversion of epichlorohydrin (ECH) at the 1 bar of CO2 pressure, at 55 °C, and a moderate catalyst amount (1 mol%), with over 99% selectivity toward the corresponding cyclic carbonate of ECH. The superior catalytic activity of PNU-25-NH2 may be attributed to its high amount of acidic-basic sites and large BET surface area in comparison with the PNU-25. The PNU-25-NH2 catalyst could be reused up to four cycles without compromising its structural integrity and the ECH conversion. The reaction mechanism of CO2 and ECH cycloaddition reaction mediated by the PNU-25-NH2 was investigated in detail based on the experimental inferences and periodic calculations of density functional theory (DFT). The energy barrier of the rate-determining step of the PNU-25-NH2/TBAB-catalyzed reaction was significantly lower than those of the rate-determining steps of un-catalyzed and TBAB-catalyzed reactions.
  • Racemic alcohols to optically pure amine precursors enabled by catalyst dynamic kinetic resolution: experiment and computation

    Azofra, Luis Miguel; Tran, Mai Anh; Zubar, Viktoriia; Cavallo, Luigi; Rueping, Magnus; El-Sepelgy, Osama (Chemical Communications, Royal Society of Chemistry (RSC), 2020-06-29) [Article]
    <p>An unprecedented base metal catalysed asymmetric synthesis of α-chiral amine precursors from racemic alcohols is reported. This redox-neutral reaction utilises a bench-stable manganese complex and Ellman’s sulfinamide as versatile ammonia...</p>
  • Significant Impact of Exposed Facets on the BiVO4 Material Performance for Photocatalytic Water Splitting Reactions

    Lardhi, Sheikha F.; Cavallo, Luigi; Harb, Moussab (The Journal of Physical Chemistry Letters, American Chemical Society (ACS), 2020-06-26) [Article]
    The impact of the four predominant (010), (110), (001), and (121) exposed facets obtained experimentally for monoclinic BiVO4 on its photocatalytic performance for water splitting reactions is investigated on the basis of the hybrid density functional theory including the spin–orbit coupling. Although their electronic structure is similar, their transport and redox properties reveal anisotropic characters based on the crystal orientation and termination. The particular role of each facet in proton reduction was correlated with the surface Bi coordination number and their geometrical distribution. Our work predicts the (001) facet as the only good candidate for both HER and OER, while the (010) facet is a fitting candidate for OER only. The (110) and (121) surfaces are acceptable candidates only for OER but less potential than (001) and (010). These outcomes will efficiently conduct experimentalists for an attentive design of facet-oriented BiVO4 samples toward improving water oxidation and proton reduction.
  • Using sodium acetate for the synthesis of [Au(NHC)X] complexes

    Scattolin, Thomas; Tzouras, Nikolaos V.; Falivene, Laura; Cavallo, Luigi; Nolan, Steven P. (Dalton Transactions, Royal Society of Chemistry (RSC), 2020-06-26) [Article]
    <p>Sodium acetate enables the synthesis of [Au(NHC)Cl] complexes, as well as their Au-alkynyl and -thiolato derivatives in high yields, under air and in technical grade, green solvents. The mild synthetic methods are also investigated computationally.</p>
  • Structurally Tunable Two-Dimensional Layered Perovskites: From Confinement and Enhanced Charge Transport to Prolonged Hot Carrier Cooling Dynamics.

    El-Ballouli, Ala’a O.; Bakr, Osman; Mohammed, Omar F. (The journal of physical chemistry letters, American Chemical Society (ACS), 2020-06-24) [Article]
    Two-dimensional (2D) layered metal halide perovskites are potential alternatives to three-dimensional perovskites in optoelectronic applications owing to their improved photostabilities and chemical stabilities. Recent investigations of 2D metal halide perovskites have demonstrated interesting optical and electronic properties of various structures that are controlled by their elemental composition and organic spacers. However, photovoltaic devices that utilize 2D perovskites suffer from poor device efficiency due to inefficient charge carrier separation and extraction. In this Perspective, we shed light on confinement control and structural variation strategies that provide better parameters for the efficient collection of charges. The influence of these strategies on the exciton binding energies, charge-carrier mobilities, hot-carrier dynamics, and electron-phonon coupling in 2D perovskites is thoroughly discussed; these parameters highlight unique opportunities for further system optimization. Beyond the tunability of these fundamental parameters, we conclude this Perspective with the most notable strategies for attaining 2D perovskites with reduced bandgaps to better suit photovoltaic applications.
  • Theoretical study of the physicochemical characteristics for Boron-Germanium BGen (n = 1–20) clusters

    Benaida, Meriem; Aiadi, Kamal Eddine; Mahtout, Sofiane; Harb, Moussab (Computational and Theoretical Chemistry, Elsevier BV, 2020-06-16) [Article]
    We present a theoretical study on the equilibrium geometries, energetic, electronic, and magnetic characteristics of BGen (n = 1–20) clusters using the density functional theory (DFT) calculations. The most stable structures display a B atom located at the surface of BGen clusters, except for BGe9, 12, 16, 18, 19, 20. Larger clusters reveal higher binding energy, suggesting their greater stability compared to the corresponding Gen+1 clusters. The calculated fragmentation energy, second-order energy difference, and HOMO-LUMO energy gap reveal that the BGe9, 12 clusters are more stable than other cluster sizes. The calculated magnetic properties of the lowest-energy BGen clusters display a total spin magnetic moment equal to 1 μB, except for the BGe cluster, which takes the value 3 μB. These findings can be useful to the experimentalists in designing new Nano-catalytic systems.
  • Illuminating Initial Carbon-Carbon Bond Formation during the Early Stages of Methane Dehydroaromatization.

    Caglayan, Mustafa; Paioni, Alessandra Lucini; Abou-Hamad, Edy; Shterk, Genrikh; Pustovarenko, Alexey; Baldus, Marc; Chowdhury, Abhishek Dutta; Gascon, Jorge (Angewandte Chemie (International ed. in English), Wiley, 2020-06-11) [Article]
    Still in 2020, methane dehydroaromatization (MDA) is among the most challenging processes in catalysis science due to the inherent harsh reaction conditions and fast catalyst deactivation. To improve it further, understanding the initial C-C bond formation mechanism is sine qua non. However, consensus about the actual reaction mechanism is still to be achieved. In this work, using advanced magic angle spinning (MAS) solid-state NMR spectroscopy, we study in detail the early stages of the reaction over a well-dispersed Mo/H-ZSM-5 catalyst. Simultaneous detection of acetylene (i.e., presumably the direct C-C bond forming product from methane), methylidene, allenes, acetal and surface-formate species along with the typical olefinic/aromatic species allow us to conclude the existence of two independent C-H activation pathways. Moreover, this study emphasizes the significance of mobility-dependent host-guest chemistry between inorganic zeolite and its organic trapped species during heterogeneous catalysis.
  • D936Y and Other Mutations in the Fusion Core of the SARS-Cov-2 Spike Protein Heptad Repeat 1 Undermine the Post-Fusion Assembly

    Cavallo, Luigi; Oliva, Romina (Cold Spring Harbor Laboratory, 2020-06-09) [Preprint]
    <jats:title>Abstract</jats:title><jats:p>The iconic “red crown” of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is made of its spike (S) glycoprotein. The S protein is the Trojan horse of coronaviruses, mediating their entry into the host cells. While SARS-CoV-2 was becoming a global threat, scientists have been accumulating data on the virus at an impressive pace, both in terms of genomic sequences and of three-dimensional structures. On April 21$^{st}/$$, the GISAID resource had collected 10,823 SARS-CoV-2 genomic sequences. We extracted from them all the complete S protein sequences and identified point mutations thereof. Six mutations were located on a 14-residue segment (929-943) in the “fusion core” of the heptad repeat 1 (HR1). Our modeling in the pre- and post-fusion S protein conformations revealed, for three of them, the loss of interactions stabilizing the post-fusion assembly. On May 29$^{th}$$, the SARS-CoV-2 genomic sequences in GISAID were 34,805. An analysis of the occurrences of the HR1 mutations in this updated dataset revealed a significant increase for the S929I and S939F mutations and a dramatic increase for the D936Y mutation, which was particularly widespread in Sweden and Wales/England. We notice that this is also the mutation causing the loss of a strong inter-monomer interaction, the D936-R1185 salt bridge, thus clearly weakening the post-fusion assembly.</jats:p>
  • Monolayer Perovskite Bridges Enable Strong Quantum Dot Coupling for Efficient Solar Cells

    Sun, Bin; Johnston, Andrew; Xu, Chao; Wei, Mingyang; Huang, Ziru; Jiang, Zhang; Zhou, Hua; Gao, Yajun; Dong, Yitong; Ouellette, Olivier; Zheng, Xiaopeng; Liu, Jiakai; Choi, Min Jae; Gao, Yuan; Baek, Se Woong; Laquai, Frédéric; Bakr, Osman; Ban, Dayan; Voznyy, Oleksandr; García de Arquer, F. Pelayo; Sargent, Edward H. (Joule, Elsevier BV, 2020-06-09) [Article]
    Solution-processed colloidal quantum dots (CQDs) are promising optoelectronic materials; however, CQD solids have, to date, exhibited either excellent transport properties but fusion among CQDs or limited transport when QDs are strongly passivated. Here, we report the growth of monolayer perovskite bridges among quantum dots and show that this enables the union of surface passivation with improved charge transport. We grow the perovskite layer after forming the CQD solid rather than introducing perovskite precursors into the quantum dot solution: the monolayer of perovskite increases interdot coupling and decreases the distance over which carriers must tunnel. As a result, we double the diffusion length relative to reference CQD solids and report solar cells that achieve a stabilized power conversion efficiency (PCE) of 13.8%, a record among Pb chalcogenide CQD solar cells.
  • Triphenylphosphine-Based Covalent Organic Frameworks and Heterogeneous Rh-P-COFs Catalysts.

    Liu, Yubing; Dikhtiarenko, Alla; Xu, Naizhang; Sun, Jiawei; Tang, Jie; Wang, Kaiqiang; Xu, Bolian; Tong, Qing; Heeres, Hero Jan; He, Songbo; Gascon, Jorge; Fan, Yining (Chemistry (Weinheim an der Bergstrasse, Germany), Wiley, 2020-06-04) [Article]
    The synthesis of phosphine-based functional covalent organic frameworks (COFs) has attracted great attention recently. Here, we present two examples of triphenylphosphine-based COFs (termed as P-COFs) with well-defined crystalline structures, high specific surface areas and good thermal stability. Furthermore, the rhodium catalysts using the obtained P-COFs as support materials show high turnover frequency (TOF) for the hydroformylation of olefins, as well as the excellent recycling performance. This work not only extended phosphine-based COFs family, but also demonstrated their application in immobilizing homogeneous metal-based (e.g., Rh-phosphine) catalysts for heterogeneous catalysis application.
  • 3D Crumpled Ultrathin 1T MoS2 for Inkjet Printing of Mg-Ion Asymmetric Micro-supercapacitors.

    Shao, Yuanlong; Fu, Jui-Han; Cao, Zhen; Song, Kepeng; Sun, Ruofan; Wan, Yi; Shamim, Atif; Cavallo, Luigi; Han, Yu; Kaner, Richard B; Tung, Vincent (ACS nano, American Chemical Society (ACS), 2020-06-02) [Article]
    Metallic molybdenum disulfide (MoS2), e.g., 1T phase, is touted as a highly promising material for energy storage that already displays a great capacitive performance. However, due to its tendency to aggregate and restack, it remains a formidable challenge to assemble a high-performance electrode without scrambling the intrinsic structure. Here, we report an electrohydrodynamic-assisted fabrication of 3D crumpled MoS2 (c-MoS2) and its formation of an additive-free stable ink for scalable inkjet printing. The 3D c-MoS2 powders exhibited a high concentration of metallic 1T phase and an ultrathin structure. The aggregation-resistant properties of the 3D crumpled particles endow the electrodes with open space for electrolyte ion transport. Importantly, we experimentally discovered and theoretically validated that 3D 1T c-MoS2 enables an extended electrochemical stable working potential range and enhanced capacitive performance in a bivalent magnesium-ion aqueous electrolyte. With reduced graphene oxide (rGO) as the positive electrode material, we inkjet-printed 96 rigid asymmetric micro-supercapacitors (AMSCs) on a 4-in. Si/SiO2 wafer and 100 flexible AMSCs on photo paper. These AMSCs exhibited a wide stable working voltage of 1.75 V and excellent capacitance retention of 96% over 20 000 cycles for a single device. Our work highlights the promise of 3D layered materials as well-dispersed functional materials for large-scale printed flexible energy storage devices.
  • Complex Star Architectures of Well-Defined Polyethylene-Based Co/Terpolymers

    Ntetsikas, Konstantinos; Zapsas, Georgios; Bilalis, Panagiotis; Gnanou, Yves; Feng, Xueyan; Thomas, Edwin L.; Hadjichristidis, Nikos (Macromolecules, American Chemical Society (ACS), 2020-05-29) [Article]
    Well-defined polyethylene (PE)-based 3-miktoarm star copolymers (PI)2PE-OH, PI2(PI′-b-PE)-OH and terpolymer PI2(PS-b-PE)-OH (PI: polyisoprene, PS: polystyrene), bearing a functional group (−OH) at the PE chain end, were synthesized by combining anionic polymerization, polyhomologation, and linking reaction with a “bridge” molecule, BF3OEt2. 4-(Dichloromethylsilyl)diphenylethylene was first synthesized and linked with anionically prepared linear PI, through titration, to afford the “living” star precursors. Subsequently, boron-linked macroinitiators were synthesized through linking reaction with BF3OEt2 for the polyhomologation of dimethylsulfoxonium methylide to produce novel PE-based miktoarm star polymers. All intermediates and final products were characterized by high-temperature size exclusion chromatography, proton nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. The microdomain morphologies of the samples were elucidated by transmission electron microscopy imaging of microtomed sections as well as small-angle and wide-angle X-ray scattering as a function of the sample temperature. Depending on the relative degree of segregation (varying with the block molecular weight and the interaction parameter between blocks) versus the crystallization temperature of the PE block, both crystallization-driven microphase separation and segregation-driven order–disorder microphase separation can take place, resulting in various domain morphologies.
  • Modulation of Broadband Emissions in Two-dimensional <100>-oriented Ruddlesden-Popper Hybrid Perovskites

    Yin, Jun; Naphade, Rounak; Gutierrez Arzaluz, Luis; Bredas, Jean-Luc; Bakr, Osman; Mohammed, Omar F. (ACS Energy Letters, American Chemical Society (ACS), 2020-05-28) [Article]
    Two-dimensional (2D) Ruddlesden−Popper (RP) perovskites are emerging materials for light-emitting applications. Unfortunately, their desirable narrowband emission coexists with broadband emissions, which limits the color quality and performance of the light source. However, the origin of such broadband emission in ⟨100⟩-oriented perovskites is still under debate. Here, we experimentally and theoretically demonstrate that unlike ⟨110⟩-oriented RP perovskites, the broadband emission of the 2D ⟨100⟩-oriented RP (PEA)2PbI4 (PEA = C6H5C2H4NH3 +) perovskites originates from defect-related luminescence centers. We find that the broadband emission of this prototype 2D structure can be largely suppressed by using excess PEAI treatment. Density functional theory (DFT) calculations indicate that iodine (I) vacancies both in the bulk and on the surface are responsible for the broadband emission. We attribute the decreased broadband emission after PEAI treatment to the passivation of both under coordinated Pb2+ ions on the surface and I vacancies in the bulk through I− ion migration.
  • Bimetallic metal-organic framework mediated synthesis of Ni-Co catalysts for the dry reforming of methane

    Khan, Il Son; Galilea, Adrian; Shterk, Genrikh; Garzon Tovar, Luis Carlos; Gascon, Jorge (Catalysts, MDPI AG, 2020-05-25) [Article]
    Dry reforming of methane (DRM) involves the conversion of CO2 and CH4, the most important greenhouse gases, into syngas, a stoichiometric mixture of H2 and CO that can be further processed via Fischer–Tropsch chemistry into a wide variety of products. However, the devolvement of the coke resistant catalyst, especially at high pressures, is still hampering commercial applications. One of the relatively new approaches for the synthesis of metal nanoparticle based catalysts comprises the use of metal-organic frameworks (MOFs) as catalyst precursors. In this work we have explored MOF-74/CPO-27 MOFs as precursors for the synthesis of Ni, Co and bimetallic Ni-Co metal nanoparticles. Our results show that the bimetallic system produced through pyrolysis of a Ni-Co@CMOF-74 precursor displays the best activity at moderate pressures, with stable performance during at least 10 h at 700◦ C, 5 bar and 33 L·h−1·g−1.
  • Impact of small promoter amounts on coke structure in dry reforming of methane over Ni/ZrO2

    Franz, Robert; Kühlewind, Tobias; Shterk, Genrikh; Abou-Hamad, Edy; Parastaev, Alexander; Uslamin, Evgeny; Hensen, Emiel J.M.; Kapteijn, Freek; Gascon, Jorge; Pidko, Evgeny A. (Catalysis Science & Technology, Royal Society of Chemistry (RSC), 2020-05-22) [Article]
    Coke deposition is one of the main challenges in the commercialisation of dry reforming of methane over supported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for the catalyst lifetime. Accordingly, in this study, we analysed the effect of Na, K, and Cs promoters on both these variables over Ni/ZrO2 catalysts. Besides blocking the most active coke-forming sites already at low loading, the promoting effect of the alkali metals is also contributed to by their coke gasification activity. To evaluate the additional impact of the latter, the behaviour of alkali-doped catalysts was compared to that for Mn-doped catalysts, exclusively featuring the site-blocking promotion mechanism. While the conversion is barely affected by the type of promoter, it has a profound effect on the amount and the composition of carbon deposits formed during the reaction. Promoting with K or Mn reduces the coke content to a similar degree but with less carbon fibres observed in the case of K. The promotion by Cs and Na results in the lowest coke content. The superior performance of Cs and Na-doped Ni/ZrO2 catalysts is attributed to the enhanced coke gasification via carbonate species on top of the site blocking effects.
  • Boosting Self-Trapped Emissions in Zero-Dimensional Perovskite Heterostructures

    Yin, Jun; Bredas, Jean-Luc; Bakr, Osman; Mohammed, Omar F. (Chemistry of Materials, American Chemical Society (ACS), 2020-05-22) [Article]
    Zero-dimensional (0D) inorganic perovskites have attracted great interest for white-light-emitting applications due to their broadband emissions originating from self-trapped excitons. In this work, we explore and decipher exciton self-trapping in a series of 0D inorganic perovskites, A4PbX6 and A4SnX6 (A = K, Rb, and Cs; X = Cl, Br, and I) at the density functional theory level within the theoretical framework of the one-dimensional configuration coordinate diagram. We demonstrate that the formation of self-trapped states in A4PbX6 and A4SnX6 can be attributed to local structural distor-tions of individual [PbX6]4- and [SnX6]4- octahedra. Importantly, with the goal of both potentially improving the stability of the Sn derivatives and enhancing the emission efficiency, we further propose and design two types of 0D perovskite heter-ostructures, bulk A4PbX6/A4SnX6 mixtures and A4PbX6/A4SnX6 heterojunctions. We find that these 0D heterostructures exhibit type-I energy level alignment, in which energy transfer from A4PbX6 to A4SnX6 is strongly promoted. Interestingly, these heterostructures show an increase in the transition dipole moments between the ground and self-trapped states compared to the pristine 0D perovskites. Our findings provide a new material design strategy for boosting self-trapped emissions with improved air stability for white-light-emitting applications.

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