Now showing items 21-40 of 3239

    • Novel Enzymes From the Red Sea Brine Pools: Current State and Potential

      Renn, Dominik; Shepard, Lera; Vancea, Alexandra; Karan, Ram; Arold, Stefan T.; Rueping, Magnus (Frontiers in Microbiology, Frontiers Media SA, 2021-10-27) [Article]
      The Red Sea is a marine environment with unique chemical characteristics and physical topographies. Among the various habitats offered by the Red Sea, the deep-sea brine pools are the most extreme in terms of salinity, temperature and metal contents. Nonetheless, the brine pools host rich polyextremophilic bacterial and archaeal communities. These microbial communities are promising sources for various classes of enzymes adapted to harsh environments – extremozymes. Extremozymes are emerging as novel biocatalysts for biotechnological applications due to their ability to perform catalytic reactions under harsh biophysical conditions, such as those used in many industrial processes. In this review, we provide an overview of the extremozymes from different Red Sea brine pools and discuss the overall biotechnological potential of the Red Sea proteome.
    • Printed Memtransistor Utilizing a Hybrid Perovskite/Organic Heterojunction Channel

      Ma, Chun; Chen, Hu; Yengel, Emre; Faber, Hendrik; Khan, Jafar Iqbal; Tang, Ming-Chun; Li, Ruipeng; Loganathan, Kalaivanan; Lin, Yuanbao; Zhang, Weimin; Laquai, Frédéric; McCulloch, Iain; Anthopoulos, Thomas D. (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-10-25) [Article]
      Neuromorphic computing has the potential to address the inherent limitations of conventional integrated circuit technology, ranging from perception, pattern recognition, to memory and decision-making ( Acc. Chem. Res. 2019, 52 (4), 964−974) ( Nature 2004, 431 (7010), 796−803) ( Nat. Nanotechnol. 2013, 8 (1), 13−24). Despite their low power consumption ( Nano Lett. 2016, 16 (11), 6724−6732), traditional two-terminal memristors can perform only a single function while lacking heterosynaptic plasticity ( Nanotechnology 2013, 24 (38), 382001). Inspired by the unconditioned reflex, multiterminal memristive transistors (memtransistor) were developed to realize complex functions, such as multiterminal modulation and heterosynaptic plasticity ( Nature 2018, 554, (7693), 500−504). Here we combine a hybrid metal halide perovskite with an organic conjugated polymer to form heterojunction transistors that are responsive to both electrical and optical stimuli. We show that the synergistic effects of photoinduced ion migration in the perovskite and electronic transport in the polymer layers can be exploited to realize memristive functions. The device combines reversible, nonvolatile conductance modulation with large switching current ratios, high endurance, and long retention times. Using in situ scanning Kelvin probe microscopy and variable-temperature charge transport measurement, we correlate the collective effects of bias-induced and photoinduced ion migration with the heterosynaptic behavior observed in this hybrid memtransistor. The hybrid heterojunction channel concept is expected to be applicable to other material combinations making it a promising platform for deployment in innovative neuromorphic devices of the future.
    • Cyanamide Passivation Enables Robust Elemental Imaging of Metal Halide Perovskites at Atomic Resolution

      Liu, Jiakai; Song, Kepeng; Zheng, Xiaopeng; Yin, Jun; Yao, Ke Xin; Chen, Cailing; Yang, Haoze; Hedhili, Mohamed N.; Zhang, Wang; Han, Peigang; Mohammed, Omar F.; Han, Yu; Bakr, Osman (The Journal of Physical Chemistry Letters, American Chemical Society (ACS), 2021-10-21) [Article]
      Lead halide perovskites (LHPs) have attracted a tremendous amount of attention because of their applications in solar cells, lighting, and optoelectronics. However, the atomistic principles underlying their decomposition processes remain in large part obscure, likely due to the lack of precise information about their local structures and composition along regions with dimensions on the angstrom scale, such as crystal interfaces. Aberration-corrected scanning transmission electron microscopy combined with X-ray energy dispersive spectroscopy (EDS) is an ideal tool, in principle, for probing such information. However, atomic-resolution EDS has not been achieved for LHPs because of their instability under electron-beam irradiation. We report the fabrication of CsPbBr3 nanoplates with high beam stability through an interface-assisted regrowth strategy using cyanamide. The ultrahigh stability of the nanoplates primarily stems from two contributions: defect-healing self-assembly/regrowth processes and surface modulation by strong electron-withdrawing cyanamide molecules. The ultrahigh stability of as-prepared CsPbBr3 nanoplates enabled atomic-resolution EDS elemental mapping, which revealed atomically and elementally resolved details of the LHP nanostructures at an unprecedented level. While improving the stability of LHPs is critical for device applications, this work illustrates how improving the beam stability of LHPs is essential for addressing fundamental questions on structure–property relations in LHPs.
    • Light and heat team up: tunable selectivity in CO2 photo-thermal reduction by perovskite-supported Pd nanoparticles

      Mateo, Diego; Maity, Partha; Shterk, Genrikh; Mohammed, Omar F.; Gascon, Jorge (ChemSusChem, Wiley, 2021-10-21) [Article]
      Photo-thermal catalysis has recently emerged as a promising alternative to overcome the limitations of traditional photocatalysis. Despite its potential, most of the photo-thermal systems still lack adequate selectivity patterns and appropriate analysis on the underlying reaction pathways, thus hampering a wide implementation. Herein, we report the preparation of a novel photocatalyst based on Pd nanoparticles (NPs) supported on barium titanate (BTO) for the selective photo-thermal reduction of CO 2 that displays catalytic rates of up to 8.2 mol CO /g Pd ·h. The photocatalyst allows for a tailored selectivity towards CO or CH 4 as a function of the metal loading or the light intensity. Mechanistic studies indicate that both thermal and non-thermal contributions of light play a role in the overall reaction pathway, each of them being dominant upon changing reaction conditions.
    • Redox induced oxidative C-C coupling of non-innocent bis(heterocyclo)methanides

      Panda, Sanjib; Baliyan, Rupal; Dhara, Suman; Huang, Kuo-Wei; Lahiri, Goutam Kumar (DALTON TRANSACTIONS, Royal Society of Chemistry (RSC), 2021-10-21) [Article]
      <jats:p>Redox driven oxidative homocoupling <jats:italic>versus</jats:italic> oxygenation of bis(heterocyclo)methanides (BHMs) has been shown to be a function of varying BHM backbones and metal precursors.</jats:p>
    • Nickel-Catalyzed Reductive Cross-Couplings: New Opportunities for Carbon–Carbon Bond Formations through Photochemistry and Electrochemistry

      Yi, Liang; Ji, Tengfei; Chen, Kun-Quan; Chen, Xiang-Yu; Rueping, Magnus (CCS Chemistry, Chinese Chemical Society, 2021-10-15) [Article]
      Metal-catalyzed cross-electrophile couplings have become a valuable tool for carbon–carbon bond formation. This minireview provides a comprehensive overview of the recent developments in the topical field of cross-electrophile couplings, provides explanations of the current state-of-the-art, and highlights new opportunities arising in the emerging fields of photoredox catalysis and electrochemistry.
    • Selectivity descriptors for the direct hydrogenation of CO2 to hydrocarbons during zeolite-mediated bifunctional catalysis

      Galilea, Adrian; Gong, Xuan; Caglayan, Mustafa; Nastase, Stefan-Adrian F.; Abou-Hamad, Edy; Gevers, Lieven; Cavallo, Luigi; Chowdhury, Abhishek Dutta; Gascon, Jorge (Nature Communications, Springer Science and Business Media LLC, 2021-10-08) [Article]
      AbstractCascade processes are gaining momentum in heterogeneous catalysis. The combination of several catalytic solids within one reactor has shown great promise for the one-step valorization of C1-feedstocks. The combination of metal-based catalysts and zeolites in the gas phase hydrogenation of CO2 leads to a large degree of product selectivity control, defined mainly by zeolites. However, a great deal of mechanistic understanding remains unclear: metal-based catalysts usually lead to complex product compositions that may result in unexpected zeolite reactivity. Here we present an in-depth multivariate analysis of the chemistry involved in eight different zeolite topologies when combined with a highly active Fe-based catalyst in the hydrogenation of CO2 to olefins, aromatics, and paraffins. Solid-state NMR spectroscopy and computational analysis demonstrate that the hybrid nature of the active zeolite catalyst and its preferred CO2-derived reaction intermediates (CO/ester/ketone/hydrocarbons, i.e., inorganic-organic supramolecular reactive centers), along with 10 MR-zeolite topology, act as descriptors governing the ultimate product selectivity.
    • Alternating Copolymerization of Epoxides with Isothiocyanates

      Chen, Chao; Gnanou, Yves; Feng, Xiaoshuang (Macromolecules, American Chemical Society (ACS), 2021-10-08) [Article]
      The ring-opening copolymerization of epoxides with isothiocyanates (ITCs) is explored for the first time. In the presence of phosphazenium benzoxide, epoxides investigated in this work including propylene oxide, ethylene oxide, and cyclohexene oxide were successfully copolymerized with both an aromatic ITC, phenyl isothiocyanate, and two aliphatic ITCs, ethyl isothiocyanate and hexyl isothiocyanate. Effects of the phosphazene bases used, of the temperature, and of the presence of Lewis acids, triethyl borane and diethyl zinc (ZnEt2), on the alternating copolymerization were investigated respectively. The thermal properties of the obtained copolymers were analyzed by differential scanning calorimetry and thermogravimetric analysis. The present work reports new ITC heteroallene monomers being alternating copolymerized with epoxides.
    • Chemical Design Rules for Non-Fullerene Acceptors in Organic Solar Cells

      Markina, Anastasia; Lin, Kun-Han; Liu, Wenlan; Poelking, Carl; Firdaus, Yuliar; Villalva, Diego Rosas; Khan, Jafar Iqbal; Paleti, Sri Harish Kumar; Harrison, George T.; Gorenflot, Julien; Zhang, Weimin; De Wolf, Stefaan; McCulloch, Iain; Anthopoulos, Thomas D.; Baran, Derya; Laquai, Frédéric; Andrienko, Denis (Advanced Energy Materials, Wiley, 2021-10-08) [Article]
      Efficiencies of organic solar cells have practically doubled since the development of non-fullerene acceptors (NFAs). However, generic chemical design rules for donor-NFA combinations are still needed. Such rules are proposed by analyzing inhomogeneous electrostatic fields at the donor–acceptor interface. It is shown that an acceptor–donor–acceptor molecular architecture, and molecular alignment parallel to the interface, results in energy level bending that destabilizes the charge transfer state, thus promoting its dissociation into free charges. By analyzing a series of PCE10:NFA solar cells, with NFAs including Y6, IEICO, and ITIC, as well as their halogenated derivatives, it is suggested that the molecular quadrupole moment of ≈75 Debye Å balances the losses in the open circuit voltage and gains in charge generation efficiency.
    • Electrolyte-gated transistors for enhanced performance bioelectronics

      Torricelli, Fabrizio; Adrahtas, Demetra Z.; Bao, Zhenan; Berggren, Magnus; Biscarini, Fabio; Bonfiglio, Annalisa; Bortolotti, Carlo A.; Frisbie, C. Daniel; Macchia, Eleonora; Malliaras, George G.; McCulloch, Iain; Moser, Maximilian; Nguyen, Thuc-Quyen; Owens, Róisín M.; Salleo, Alberto; Spanu, Andrea; Torsi, Luisa (Nature Reviews Methods Primers, Springer Science and Business Media LLC, 2021-10-07) [Article]
      Electrolyte-gated transistors (EGTs), capable of transducing biological and biochemical inputs into amplified electronic signals and stably operating in aqueous environments, have emerged as fundamental building blocks in bioelectronics. In this Primer, the different EGT architectures are described with the fundamental mechanisms underpinning their functional operation, providing insight into key experiments including necessary data analysis and validation. Several organic and inorganic materials used in the EGT structures and the different fabrication approaches for an optimal experimental design are presented and compared. The functional bio-layers and/or biosystems integrated into or interfaced to EGTs, including self-organization and self-assembly strategies, are reviewed. Relevant and promising applications are discussed, including two-dimensional and three-dimensional cell monitoring, ultra-sensitive biosensors, electrophysiology, synaptic and neuromorphic bio-interfaces, prosthetics and robotics. Advantages, limitations and possible optimizations are also surveyed. Finally, current issues and future directions for further developments and applications are discussed.
    • Unraveling the Unconventional Order of a High-Mobility Indacenodithiophene–Benzothiadiazole Copolymer

      Cendra, Camila; Balhorn, Luke; Zhang, Weimin; O’Hara, Kathryn; Bruening, Karsten; Tassone, Christopher J.; Steinrück, Hans-Georg; Liang, Mengning; Toney, Michael F.; McCulloch, Iain; Chabinyc, Michael L; Salleo, Alberto; Takacs, Christopher J. (ACS Macro Letters, American Chemical Society (ACS), 2021-10-05) [Article]
      A new class of donor–acceptor (D–A) copolymers found to produce high charge carrier mobilities competitive with amorphous silicon (>1 cm2 V–1 s–1) exhibit the puzzling microstructure of substantial local order, however lacking long-range order and crystallinity previously deemed necessary for achieving high mobility. Here, we demonstrate the application of low-dose transmission electron microscopy to image and quantify the nanoscale and mesoscale organization of an archetypal D–A copolymer across areas comparable to electronic devices (≈9 μm2). The local structure is spatially resolved by mapping the backbone (001) spacing reflection, revealing nanocrystallites of aligned polymer chains throughout nearly the entire film. Analysis of the nanoscale structure of its ordered domains suggests significant short- and medium-range order and preferential grain boundary orientations. Moreover, we provide insights into the rich, interconnected mesoscale organization of this new family of D–A copolymers by analysis of the local orientational spatial autocorrelations.
    • The Complex Crystal Structure and Abundant Local Defects of Zeolite EMM-17 Unraveled by Combined Electron Crystallography and Microscopy

      Liu, Xiaona; Liu, Lingmei; Pan, Tingting; Yan, Nana; Dong, Xinglong; Li, Yuanhao; Chen, Lu; Tian, Peng; Han, Yu; Guo, Peng; Liu, Zhongmin (Angewandte Chemie International Edition, Wiley, 2021-10-04) [Article]
      Structure determination of zeolites is of great significance for understanding their fascinating properties. In this study, we successfully solve one of polymorphic structures (polymorph A) of zeolite EMM-17, which can only crystallize in sub-micron-sized crystals while containing complex stacking disorders, from the three-dimensional (3D) electron diffraction (ED) data. This is the first time that the atomic structure of this polymorph has been ab initio solved, and the result reveals a unique 10(12) X 10(12) X 11-ring channel system. Moreover, we acquire the first atomic-resolution images of EMM-17 using integrated differential phase-contrast scanning transmission electron microscopy. The images allow us to directly observe polymorphs B and C and discover a large number of local structural defects. Based on structural features unraveled from the reciprocal-space 3D ED data and real-space images, we propose a series of energetically feasible local structures in EMM-17. In addition, we demonstrate that the unique porous structure of EMM-17 enables efficient kinetic separation of C6 alkane isomers.
    • Understanding Halide Counterion Effects in Enantioselective Ruthenium-Catalyzed Carbonyl (α-Aryl)allylation: Alkynes as Latent Allenes and Trifluoroethanol-Enhanced Turnover in The Conversion of Ethanol to Higher Alcohols via Hydrogen Auto-transfer

      Ortiz, Eliezer; Shezaf, Jonathan Z.; Chang, Yu-Hsiang; Goncalves, Theo; Huang, Kuo-Wei; Krische, Michael J. (Journal of the American Chemical Society, American Chemical Society (ACS), 2021-10-04) [Article]
      Crystallographic characterization of RuX(CO)(η3-C3H5)(JOSIPHOS), where X = Cl, Br, or I, reveals a halide-dependent diastereomeric preference that defines metal-centered stereogenicity and, therefrom, the enantioselectivity of C-C coupling in ruthenium-catalyzed anti-diastereo- and enantioselective C-C couplings of primary alcohols with 1-aryl-1-propynes to form products of carbonyl anti-(α-aryl)allylation. Computational studies reveal that a non-classical hydrogen bond between iodide and the aldehyde formyl CH bond stabilizes the favored transition state for carbonyl addition. An improved catalytic system enabling previously unattainable transformations was developed that employs an iodide-containing precatalyst, RuI(CO)3(η3-C3H5), in combination with trifluoroethanol, as illustrated by the first enantioselective ruthenium-catalyzed C-C couplings of ethanol to form higher alcohols.
    • Boron-Catalyzed Polymerization of Phenyl-Substituted Allylic Arsonium Ylides toward Nonconjugated Emissive Materials from C3/C1 Monomeric Units

      Liu, Pibo; Hadjichristidis, Nikos (ACS Macro Letters, American Chemical Society (ACS), 2021-10-04) [Article]
      Two novel allylic arsonium ylide monomers with a phenyl (steric and electronic effect) group at different positions were synthesized and used in boron-catalyzed polymerization to produce a series of well-defined polymers, poly(2-phenyl-propenylene-co-2-phenyl-propenylidene) (P2-PhAY) and poly(3-phenyl-propenylene-co-3-phenyl-propenylidene) (P3-PhAY), with unusual structures but a controllable molecular weight and relatively low polydispersity. The backbone of these polymers consists of a mixture of C1 (chain grows by one carbon atom at a time) and C3 (chain grows by three carbon atoms at a time) monomeric units, as determined by 1H, 13C, and 1H–13C HSQC 2D NMR. Based on the experimental results and density functional theoretical (DFT) calculations, we were able to propose a mechanism that takes into account not only the steric hindrance, but also the electron effect of the phenyl group. In addition, a nontraditional intrinsic luminescence was observed from the nonconjugated P2-PhAY and P3-PhAY; such unexpected emission is attributed to the formation of C3-unit clusters, as evidenced by ultraviolet–visible and fluorescence spectroscopy.
    • Advances and Challenges in Tin Halide Perovskite Nanocrystals

      Chen, Jia-Kai; Zhang, Bin-Bin; Liu, Qi; Shirahata, Naoto; Mohammed, Omar F.; Bakr, Osman; Sun, Hong-Tao (ACS Materials Letters, American Chemical Society (ACS), 2021-10-01) [Article]
      A major application limit for lead halide perovskite nanocrystals (NCs) is the presence of the highly toxic lead element, raising critical concerns of environmental pollution and health problems. To address this issue, tin halide perovskite NCs have been pushed to the forefront of perovskite research owing to their eco-friendly merit and tantalizing photophysical properties. In this Review, we critically summarize and assess the latest advances in the synthesis approaches of tin halide perovskite NCs including the hot injection, ligand-assisted reprecipitation, and chemical vapor deposition. More specifically, we detail the state-of-the-art preliminary studies in modulating their photophysical properties and in enhancing the stability with a variety of strategies such as precursor engineering, ligand engineering, and alloyed structure construction. Finally, we highlight the remaining challenges that need to be overcome to attain tin halide perovskite NCs with clear structure–property relationships and comparable physical and chemical properties to their lead-based cousins.
    • A molecular design approach towards elastic and multifunctional polymer electronics

      Zheng, Yu; Yu, Zhiao; Zhang, Song; Kong, Xian; Michaels, Wesley; Wang, Weichen; Chen, Gan; Liu, Deyu; Lai, Jian-Cheng; Prine, Nathaniel; Zhang, Weimin; Nikzad, Shayla; Cooper, Christopher B.; Zhong, Donglai; Mun, Jaewan; Zhang, Zhitao; Kang, Jiheong; Tok, Jeffrey B.-H.; McCulloch, Iain; Qin, Jian; Gu, Xiaodan; Bao, Zhenan (Nature Communications, Springer Science and Business Media LLC, 2021-09-29) [Article]
      Next-generation wearable electronics require enhanced mechanical robustness and device complexity. Besides previously reported softness and stretchability, desired merits for practical use include elasticity, solvent resistance, facile patternability and high charge carrier mobility. Here, we show a molecular design concept that simultaneously achieves all these targeted properties in both polymeric semiconductors and dielectrics, without compromising electrical performance. This is enabled by covalently-embedded in-situ rubber matrix (iRUM) formation through good mixing of iRUM precursors with polymer electronic materials, and finely-controlled composite film morphology built on azide crosslinking chemistry which leverages different reactivities with C–H and C=C bonds. The high covalent crosslinking density results in both superior elasticity and solvent resistance. When applied in stretchable transistors, the iRUM-semiconductor film retained its mobility after stretching to 100% strain, and exhibited record-high mobility retention of 1 cm2 V−1 s−1 after 1000 stretching-releasing cycles at 50% strain. The cycling life was stably extended to 5000 cycles, five times longer than all reported semiconductors. Furthermore, we fabricated elastic transistors via consecutively photo-patterning of the dielectric and semiconducting layers, demonstrating the potential of solution-processed multilayer device manufacturing. The iRUM represents a molecule-level design approach towards robust skin-inspired electronics.
    • One-Pot Chemoenzymatic Conversion of Alkynes to Chiral Amines

      Mathew, Sam; Sagadevan, Arunachalam; Renn, Dominik; Rueping, Magnus (ACS Catalysis, American Chemical Society (ACS), 2021-09-29) [Article]
      A one-pot chemoenzymatic sequential cascade for the synthesis of chiral amines from alkynes was developed. In this integrated approach, just ppm amounts of gold catalysts enabled the conversion of alkynes to ketones (>99%) after which a transaminase was used to catalyze the production of biologically valuable chiral amines in a good yield (up to 99%) and enantiomeric excess (>99%). A preparative scale synthesis of (S)-methylbenzylamine and (S)-4-methoxy-methylbenzylamine from its alkyne form gave a yield of 59 and 92%, respectively, with ee > 99%.
    • Single-Particle Spectroscopy as a Versatile Tool to Explore Lower-Dimensional Structures of Inorganic Perovskites

      Bose, Riya; Zhou, Xiaohe; Guo, Tianle; Yang, Haoze; Yin, Jun; Mishra, Aditya; Slinker, Jason D.; Bakr, Osman; Mohammed, Omar F.; Malko, Anton V. (ACS Energy Letters, American Chemical Society (ACS), 2021-09-27) [Article]
      The remarkable defect-tolerant nature of inorganic cesium halide perovskites, leading to near unity photoluminescence (PL) quantum yield and narrow emission line width across the entire visible spectrum, has provided a tantalizing platform for the development of a plethora of light-emitting applications. Recently, lower-dimensional (2D, 1D, and 0D) perovskites have attracted further attention due to their enhanced thermal, photo, and chemical stability as compared to their three-dimensional (3D) analogues. The combination of external size quantization and internal octahedral organization provides a unique opportunity to study and harness “multi-dimensional” electronic properties engineered on both atomic scale and nanoscale. However, crucial research to understand the elementary charge carrier dynamics in lower-dimensional perovskites lags far behind the enormous effort to incorporate them into optoelectronic devices. In this Perspective, we provide a review of recent developments that focus on studies of the dynamics of excitonic complexes in Cs-based perovskite nanocrystals using single-particle time-resolved PL spectroscopy and photon correlation measurements. Single-photon statistical studies not only offer an unprecedented level of detail to directly assess various recombination pathways, but also provide insights into specifics of the charge carriers' localization. We discuss the underlying physicochemical processes that govern PL emission and draw attention to a number of attributes within this class of the materials, especially lower-dimensional perovskites, that may indicate the common origin of the PL emission as well as provide a route map for the vast unexplored territories where single-particle spectroscopy can be a powerful tool to unravel crucial information.
    • Fluorinated thin-film composite membranes for nonpolar organic solvent nanofiltration

      Alduraiei, Fadhilah H.; Manchanda, Priyanka; Pulido Ponce de Leon, Bruno Antonio; Szekely, Gyorgy; Nunes, Suzana Pereira (Separation and Purification Technology, Elsevier BV, 2021-09-23) [Article]
      Polyamide (PA) is highly effective as a selective layer in case of nanofiltration (NF) membranes, mainly for filtering water and other polar solvents. The incorporation of fluorinated monomers in a polyamide network is a novel strategy for obtaining membranes with enhanced permeability in case of nonpolar solvents. In this study, PA thin-film composite membranes were prepared by interfacially reacting trimesoyl chloride (TMC) and 4,4ʹ-(hexafluoroisopropylidene)bis(benzoyl chloride) (HFBC) in an organic phase with 5-trifluoromethyl-1,3-phenylenediamine (TFMPD) in an aqueous phase in a single step. The resulting membrane obtained using HFBC exhibited a considerably increased nonpolar solvent flux and selectivity in the nanofiltration range. Thus, the hydrophobicity of the PA layer and its permeance are effectively enhanced because of the incorporation of the fluorinated monomer. Therefore, high-performance membranes can be obtained for nonpolar solvent separation in petroleum refineries and purification in the pharmaceutical industry.
    • Spin–Orbit Charge-Transfer Intersystem Crossing of Compact Naphthalenediimide-Carbazole Electron-Donor–Acceptor Triads

      Hussain, Mushraf; El-Zohry, Ahmed; Hou, Yuqi; Toffoletti, Antonio; Zhao, Jianzhang; Barbon, Antonio; Mohammed, Omar F. (The Journal of Physical Chemistry B, American Chemical Society (ACS), 2021-09-20) [Article]
      Compact electron donor-acceptor triads based on carbazole (Cz) and naphthalenediimide (NDI) were prepared to study the spin-orbit charge-transfer intersystem crossing (SOCT-ISC). By variation of the molecular conformation and electron-donating ability of the carbazole moieties, the electronic coupling between the two units was tuned, and as a result charge-transfer (CT) absorption bands with different magnitudes were observed (ε = 4000-18 000 M<sup>-1</sup> cm<sup>-1</sup>). Interestingly, the triads with NDI attached at the 3-C position or with a phenyl spacer at the <i>N</i> position of the Cz moiety, thermally activated delayed fluorescence (TADF) was observed. Femtosecond transient absorption (fs-TA) spectroscopy indicated fast electron transfer (0.8-1.5 ps) from the Cz to NDI unit, followed by population of the triplet state (150-600 ps). Long-lived triplet states (up to τ<sub>T</sub> = 45-50 μs) were observed for the triads. The solvent-polarity-dependent singlet-oxygen quantum yield (Φ<sub>Δ</sub>) is 0-26%. Time-resolved electron paramagnetic resonance (TREPR) spectral study of TADF molecules indicated the presence of the <sup>3</sup>CT state for <b>NDI-Cz-Ph</b> (zero-field-splitting parameter <i>D</i> = 21 G) and an <sup>3</sup>LE state for <b>NDI-Ph-Cz</b> (<i>D</i> = 586 G). The triads were used as triplet photosensitizers in triplet-triplet annihilation upconversion by excitation into the CT absorption band; the upconversion quantum yield was Φ<sub>UC</sub> = 8.2%, and there was a large anti-Stokes shift of 0.55 eV. Spatially confined photoexcitation is achieved with the upconversion using focusing laser beam excitation, and not the normally used collimated laser beam, i.e., the upconversion was only observed at the focal point of the laser beam. Photo-driven intermolecular electron transfer was demonstrated with reversible formation of the NDI<sup>-•</sup> radical anion in the presence of the sacrificial electron donor triethanolamine.