Identifying (BN)2-pyrene as a new class of singlet fission chromophores: significance of azaborine substitution

Singlet fission converts one photoexcited singlet state to two triplet excited states and raises photoelectric conversion efficiency in photovoltaic devices. However, only a handful of chromophores have been known to undergo this process, which greatly limits the application of singlet fission in photovoltaics. We hereby identify a recently synthesized diazadiborine-pyrene ((BN)2-pyrene) as a singlet fission chromophore. Theoretical calculations indicate that it satisfies the thermodynamics criteria for singlet fission. More importantly, the calculations provide a physical chemistry insight into how the BN substitution makes this happen. Both calculation and transient absorption spectroscopy experiment indicate that the chromophore has a better absorption than pentacene. The convenient synthesis pathway of the (BN)2-pyrene suggests an in situ chromophore generation in photovoltaic devices. Two more (BN)2-pyrene isomers are proposed as singlet fission chromophores. This study sets a step forward in the cross-link of singlet fission and azaborine chemistry

Automated reasoning with function evaluation for COCOLOG

We introduced a logic for the study of dynamical control systems which we called a Conditional Observer Logic for finite machines (Cocolog). In that paper the properties of consistency and completeness for each first order logical theory in the tree of such theories in a Cocolog were established. The efficacy of automatic theorem proving is a crucial issue in the implementation of Cocolog. In this paper, we present a function evaluation based resolution, called FE-resolution, for Cocolog. The unique model property of Cocolog is first proved via the complete axiomatization property and then the decidability property of any theory in a Cocolog is deduced. Finally, completeness and complexity reduction of FE-resolution is discussed in terms of relative truthfulness and validity

COCOLOG: a conditional observer and controller logic for finite machines

The problem of observation and control for partially observed input-state-output machines is formulated in terms of a tree of first order logical theories. A set of first order languages for the description of the controlled evolution and state estimation of any given machine M is specified ; further, conditional control axioms are formulated so that closed loop control actions occur when specified past observation dependent conditions are fulfilled. In particular, conditional control axioms may include commands that steer the system state from a current partially observed state (estimate) to a target state, if such of sequence of controls can be proven to exist. Starting from a general theory of M at the initial instant, observations on the input-output behaviour of the system at any later instant are accepted by the system as new axioms these are then used together with the previously generated theory to generate the current theory. We use the acronym Cocolog to denote the family of first order conditional observer and controller logics for any given input-state-output system. A semantics is supplied for each Cocolog in terms of interpretations of controlled transitions on a tree indexed by the possible sequences of input-output observations. Extra-logical rules relating members of the family of theories of a Cocolog are then presented in the form of meta-level axioms and inference rules. In this paper consistency and completeness of the first order theories in a Cocolog family are established, decidability is obtained using a unique model property and examples of the operation of a Cocolog logic control system are given

Threshold Recognition Based on Non-stationarity of Extreme Rainfall in the Middle and Lower Reaches of the Yangtze River Basin

Analyzing the hydrological sequence from the non-stationary characteristics can better understand the responses of changes in extreme rainfall to climate change. Taking the plain area in the middle and lower reaches of the Yangtze River basin (MLRYRB) as the study area, this study adopted a set of extreme rainfall indices and used the Bernaola-Galvan Segmentation Algorithm (BGSA) method to test the non-stationarity of extreme rainfall events. The General Pareto Distribution (GPD) was used to fit extreme rainfall and was calculated to select the optimal threshold of extreme rainfall. In addition, the cross-wavelet technique was used to explore the correlations of extreme rainfall with El Niño-Southern Oscillation (ENSO) and Western Pacific Subtropical High (WPSH) events. The results showed that: (1) extreme rainfall under different thresholds had different non-stationary characteristics; (2) the GPD distribution could well fit the extreme rainfall in the MLRYRB, and 40–60 mm was considered as the suitable optimal threshold by comparing the uncertainty of the return period; and (3) ENSO and WPSH had significant periodic effects on extreme rainfall in the MLRYRB. These findings highlighted the significance of non-stationary assumptions in hydrological frequency analysis, which were of great importance for hydrological forecasting and water conservancy project management

Self Assembly of Copper(I) and Silver(I) Butterfly Clusters with 2-Mercaptothiazoline

X-ray data obtained from poor crystals which formed from the reaction of copper(II) acetate with 2-mercaptothiazoline reveal the formation of a product that is a polymer formed of tetranuclear, butterfly shaped Cu4(MT)4, 1, clusters. Preparation, isolation and structural characterization of a series of isostructural butterfly complexes was accomplished by addition of a Lewis base (pyridine, PPh3, or ASPI13) to the precipitate obtained from the reaction of copper(II) and/or silver(I) acetate with the appropriate stoichiometric amount of 2-mercaptothiazoline. The general formula of these clusters is L2M4(MT)4; 2, L = PPI13 and M = Cu; 3, L = AsPh3 and M = Cu; 6, L = PPI13 and M = Ag; MT = C3H4NS2_, known as 2-mer- captothiazolinate. The polymer [pyCu4(MT)4]„, 4, formed by the addition of pyridine to 1, was also characterized crystallographically. A mixed metal butterfly complex, (PPh3)2Ag2Cu2(MT)4, 8, is formed by addition of PPI13 to a suspension of the precipitate formed upon reaction of the free HMT ligand with a 1:1 mixture of copper(II) and silver(I) acetates in CH2CI2. FD-MS results of each of the precipitates obtained from the metal acetates and the free ligand indicate that the monomeric unit is M4(MT)4. 1H-NMR and 31P{1H}-NMR, both in solution and in the solid state are presented and interpreted

Intramolecular borylation via sequential B-Mes bond cleavage for the divergent synthesis of B,N,B-doped benzo[4]helicenes

Authors thank the Natural Sciences and Engineering Research Council of Canada and the Leverhulme Trust (RPG-2016-47) for financial support. J. A. Knöller thanks the Baden Württemberg Stiftung for a scholarship as well as Queen's and Stuttgart University for enabling this research through the Dual Degree Masters program.New symmetric and unsymmetric B,N,B-doped benzo[4]helicenes 3 - 6a/b have been achieved in good yields, using a three-step process, starting from N(tolyl)3 in a highly divergent manner (7 examples). A borinic acid functionalized 1,4-B,N- anthracene 1 was found to display unprecedented reactivity, acting as a convenient and highly effective precursor for selective formation of bromo substituted B,N,B-benzo[4]helicenes 2a/2b via intramolecular borylation and sequential B-Mes bond cleavage in presence of BBr3. Subsequent reaction of 2a/2b with Ar-Li provided a highly effective toolbox for the preparation of symmetrically/unsymmetrically functionalized B,N,B-helicenes. Their high photoluminescence quantum yields along with the small ∆EST suggest the potential as thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs).PostprintPeer reviewe

Probing thermally-induced structural evolution during the synthesis of layered Li-, Na-, or K-containing 3d transition-metal oxides

Layered alkali-containing 3d transition-metal oxides are of the utmost importance in the use of electrode materials for advanced energy storage applications such as Li-, Na-, or K-ion batteries. A significant challenge in the field of materials chemistry is understanding the dynamics of the chemical reactions between alkali-free precursors and alkali species during the synthesis of these compounds. In this study, in situ high-resolution synchrotron-based X-ray diffraction was applied to reveal the Li/Na/K-ion insertion-induced structural transformation mechanism during high-temperature solid-state reaction. The in situ diffraction results demonstrate that the chemical reaction pathway strongly depends on the alkali-free precursor type, which is a structural matrix enabling phase transitions. Quantitative phase analysis identifies for the first time the decomposition of lithium sources as the most critical factor for the formation of metastable intermediates or impurities during the entire process of Li-rich layered Li[Li0.2Ni0.2Mn0.6]O2 formation. Since the alkali ions have different ionic radii, Na/K ions tend to be located on prismatic sites in the defective layered structure (Na2/3-x[Ni0.25Mn0.75]O2 or K2/3-x[Ni0.25Mn0.75]O2) during calcination, whereas the Li ions prefer to be localized on the tetrahedral and/or octahedral sites, forming O-type structures

Structural Origin of Suppressed Voltage Decay in Single‐Crystalline Li‐Rich Layered Li[Li0.2_{0.2}Ni0.2_{0.2}Mn0.6_{0.6}]O2_{2} Cathodes

Lithium- and manganese-rich layered oxides (LMLOs, ≥ 250 mAh g$^{−1}$) with polycrystalline morphology always suffer from severe voltage decay upon cycling because of the anisotropic lattice strain and oxygen release induced chemo-mechanical breakdown. Herein, a Co-free single-crystalline LMLO, that is, Li[Li$_{0.2}$Ni$_{0.2}$Mn$_{0.6}$]O$_{2}$ (LLNMO-SC), is prepared via a Li$^+$/Na$^+$ ion-exchange reaction. In situ synchrotron-based X-ray diffraction (sXRD) results demonstrate that relatively small changes in lattice parameters and reduced average micro-strain are observed in LLNMO-SC compared to its polycrystalline counterpart (LLNMO-PC) during the charge–discharge process. Specifically, the as-synthesized LLNMO-SC exhibits a unit cell volume change as low as 1.1% during electrochemical cycling. Such low strain characteristics ensure a stable framework for Li-ion insertion/extraction, which considerably enhances the structural stability of LLNMO during long-term cycling. Due to these peculiar benefits, the average discharge voltage of LLNMO-SC decreases by only ≈0.2 V after 100 cycles at 28 mA g$^{-1}$ between 2.0 and 4.8 V, which is much lower than that of LLNMO-PC (≈0.5 V). Such a single-crystalline strategy offers a promising solution to constructing stable high-energy lithium-ion batteries (LIBs)