A Stable Triplet-Ground-State Conjugated Diradical Based on a Diindenopyrazine Skeleton.

High-spin conjugated radicals have great potential in magnetic materials and organic spintronics. However, to obtain high-spin conjugated radicals is still quite challenging due to their poor stability. We report the successful synthesis and isolation of a stable triplet conjugated diradical, 10,12-diaryldiindeno[1,2-b:2',1'-e]pyrazine (m-DIP). With the m-xylylene analogue skeleton containing electron-deficient sp2 -nitrogen atoms, m-DIP displays significant aromatic character within its pyrazine ring and its spin density mainly delocalizes on the meta-pyrazine unit, making it a triplet ground state conjugated diradical. Our work provides an effective "spin density tuning" strategy for stable high-spin conjugated radicals.

Persistent Conjugated Backbone and Disordered Lamellar Packing Impart Polymers with Efficient n-Doping and High Conductivities.

Solution-processable highly conductive polymers are of great interest in emerging electronic applications. For p-doped polymers, conductivities as high a nearly 105 S cm-1 have been reported. In the case of n-doped polymers, they often fall well short of the high values noted above, which might be achievable, if much higher charge-carrier mobilities determined could be realized in combination with high charge-carrier densities. This is in part due to inefficient doping and dopant ions disturbing the ordering of polymers, limiting efficient charge transport and ultimately the achievable conductivities. Here, n-doped polymers that achieve a high conductivity of more than 90 S cm-1 by a simple solution-based co-deposition method are reported. Two conjugated polymers with rigid planar backbones, but with disordered crystalline structures, exhibit surprising structural tolerance to, and excellent miscibility with, commonly used n-dopants. These properties allow both high concentrations and high mobility of the charge carriers to be realized simultaneously in n-doped polymers, resulting in excellent electrical conductivity and thermoelectric performance.

Amination of the Gd@C82 endohedral fullerene: tunable substitution effect on quantum coherence behaviors.

The core-shell structure of endohedral fullerene-based anisotropic magnetic molecules of high spin with long coherence time could help scale up quantum systems. In this research, by amination of Gd@C82 with morpholine, three derivatives are functionalized with 5, 7 and 9 morpholine groups providing an interesting model to investigate the relationship between the quantum coherence and the spin environment. The original radical located on the carbon cage is successfully quenched, affording a quantum phase memory times (T M) over 5 µs at 5 K. By increasing the number of substitution groups, spin-lattice relaxation times (T 1) also show significant enhancement due to the interaction variation between the molecules and the environments. We found that the T M of the three molecules show no obvious difference below 10 K, while they are limited by T 1 at higher temperatures. In this work, the variable functional groups are able to tune both T 1 and T M, offering the possibility for application of high-spin magnetic molecules in the field of quantum information processing.

Modification of TiO2 Nanoparticles with Organodiboron Molecules Inducing Stable Surface Ti3+ Complex.

As one of the most promising semiconductor oxide materials, titanium dioxide (TiO2) absorbs UV light but not visible light. To address this limitation, the introduction of Ti3+ defects represents a common strategy to render TiO2 visible-light responsive. Unfortunately, current hurdles in Ti3+ generation technologies impeded the widespread application of Ti3+ modified materials. Herein, we demonstrate a simple and mechanistically distinct approach to generating abundant surface-Ti3+ sites without leaving behind oxygen vacancy and sacrificing one-off electron donors. In particular, upon adsorption of organodiboron reagents onto TiO2 nanoparticles, spontaneous electron injection from the diboron-bound O2- site to adjacent Ti4+ site leads to an extremely stable blue surface Ti3+‒O-· complex. Notably, this defect generation protocol is also applicable to other semiconductor oxides including ZnO, SnO2, Nb2O5, and In2O3. Furthermore, the as-prepared photoelectronic device using this strategy affords 103-fold higher visible light response and the fabricated perovskite solar cell shows an enhanced performance.

[Leaf functional traits and nutrient resorption among major silviculture tree species in coastal sandy site.] / æ»¨æµ·æ²™åœ°ä¸»è¦é€ æž—æ ‘ç§å¶ç‰‡åŠŸèƒ½æ€§çŠ¶åŠå »åˆ†é‡å¸æ”¶ç‰¹å¾.

To understand the adaptative strategies of different tree species to drought and nutrient-deficient environment in coastal sandy site, leaf functional traits and nutrient resorption of four major silviculture tree species, i.e., Casuarina equisetifolia, Pinus elliottii, Acasia crassicarpa and Eucalyptus urophylla × E. grandis were analyzed. Leaf area and specific leaf area of coniferous species (C. equisetifolia and P. elliottii) were significantly lower, and leaf dry matter content and leaf thickness were significantly higher than those of broadleaved species (A. crassicarpa and E. urophy-lla × E. grandis). Nitrogen and P contents of mature leaf and leaf litter in broadleaved species were higher than those in coniferous species. Nitrogen and P contents of mature leaf were higher than those in leaf litter, but N:P was lower than that in leaf litter. Nitrogen and P resorption efficiencies were higher in coniferous species than those in broadleaved species. The P resorption efficiency in all species was significantly higher than N resorption efficiency. The N resorption efficiency of C. equisetifolia, P. elliottii, A. crassicarpa and E. urophylla × E. grandis was 64.2%, 63.1%, 47.0% and 16.8%, and the P resorption efficiency was 92.5%, 81.6%, 80.3% and 18.0%, respectively. The specific leaf area was significantly positively correlated with leaf N and P contents, but negatively correlated with leaf dry matter content, leaf thickness, and nutrient resorption efficiency. Leaf dry matter content was significantly positively correlated with leaf thickness and nutrient resorption efficiency. Therefore, C. equisetifolia and P. elliottii belonged to slow investment species with a higher nutrient resorption efficiency, while A. crassicarpa and E. urophylla × E. grandis belonged to fast investment species with lower nutrient resorption efficiency. Different tree species developed different adaptive strategies to coastal sandy environments through the interactions between leaf functional traits and nutrient resorption.

Rigid Coplanar Polymers for Stable n-Type Polymer Thermoelectrics.

Low n-doping efficiency and inferior stability restrict the thermoelectric performance of n-type conjugated polymers, making their performance lag far behind of their p-type counterparts. Reported here are two rigid coplanar poly(p-phenylene vinylene) (PPV) derivatives, LPPV-1 and LPPV-2, which show nearly torsion-free backbones. The fused electron-deficient rigid structures endow the derivatives with less conformational disorder and low-lying lowest unoccupied molecular orbital (LUMO) levels, down to -4.49 eV. After doping, two polymers exhibited high n-doping efficiency and significantly improved air stability. LPPV-1 exhibited a high conductivity of up to 1.1 S cm-1 and a power factor as high as 1.96 µW m-1 K-2 . Importantly, the power factor of the doped LPPV-1 thick film degraded only 2 % after 7 day exposure to air. This work demonstrates a new strategy for designing conjugated polymers, with planar backbones and low LUMO levels, towards high-performance and potentially air-stable n-type polymer thermoelectrics.

Single-Crystal Study of a Low Spin Co(II) Molecular Qubit: Observation of Anisotropic Rabi Cycles.

A mononuclear low spin ( S = 1/2) Co(II) molecule crystallized in a 4-fold symmetry is fully investigated by CW and pulsed EPR on a single crystal sample. The quantum phase memory time of the molecule around 1 µs at 5 K is direction-independent, while the Rabi oscillation frequency is anisotropic. The spin Hamiltonian analyses reveal that the anisotropic Landé factor and hyperfine tensor do not influence the anisotropy apparently when the microwave magnetic field is applied along a certain direction. It is considered that the possibly involved nuclear spin forbidden transitions may be responsible for the small distinction of Rabi frequencies in two directions.

Qubit crossover in the endohedral fullerene Sc3C2@C80.

The core-shell structure of endohedral fullerenes results in good protection of the encapsulated spin carriers from the environment. In this research, the quantum coherence behavior of the endohedral fullerene Sc3C2@C80 in CS2 solution is characterized from 5 K to room temperature. Below the critical temperature of around 140 K, the inner group is hindered, and the EPR spectrum consists of a single broad line. The spin carriers display a maximum phase memory time of 17.2(7) µs at 10 K. In the high temperature region, the inner group is mobile, and the EPR spectrum consists of 22 homogeneously broadened lines due to isotropic hyperfine coupling. The maximum phase memory time for each transition is around 139(1) ns at 200 K which allows arbitrary superposition state manipulations to be performed. This research demonstrates that Sc3C2@C80 displays temperature-crossover behaviour due to weak interaction between the Sc3C2 core and the C80 shell.

Chemical Modification toward Long Spin Lifetimes in Organic Conjugated Radicals.

Organic semiconductors for spin-based devices require long spin relaxation times. Understanding their spin relaxation mechanisms is critical to organic spintronic devices and applications for quantum information processing. However, reports on the spin relaxation mechanisms of organic conjugated molecules are rare and the research methods are also limited. Herein, we study the molecular design and spin relaxation mechanisms by systematically varying the structure of a conjugated radical. We found that solid-state relaxation times of organic materials are largely different from that in solution state. We demonstrate that substitution of a lower gyromagnetic ratio nucleus (e. g. D, Cl) on the para-position of the aryl rings in the triphenylmethyl (TM) radical can significantly improve their coherence times (Tm ). Flexible thin films based on such radicals exhibit ultra-long spin-lattice relaxation times (T1 ) up to 35.6(6) µs and Tm up to 1.08(4) µs under ambient conditions, which are among the longest values in films. More importantly, using the TM radical derivative (5CM), we observed room-temperature quantum coherence and Rabi cycles in thin film for the first time, suggesting that organic conjugated radicals have great potentials for spin-based information processing.

A Bio-inspired Cu4 O4 Cubane: Effective Molecular Catalysts for Electrocatalytic Water Oxidation in Aqueous Solution.

Inspired by the cubic Mn4 CaO5 cluster of natural oxygen-evolving complex in Photosystem II, tetrametallic molecular water oxidation catalysts, especially M4 O4 cubane-like clusters (M=transition metals), have aroused great interest in developing highly active and robust catalysts for water oxidation. Among these M4 O4 clusters, however, copper-based molecular catalysts are poorly understood. Now, bio-inspired Cu4 O4 cubanes are presented as effective molecular catalysts for electrocatalytic water oxidation in aqueous solution (pH 12). The exceptional catalytic activity is manifested with a turnover frequency (TOF) of 267 s-1 for [(LGly -Cu)4 ] at 1.70 V and 105 s-1 for [(LGlu -Cu)4 ] at 1.56 V. Electrochemical and spectroscopic study revealed a successive two-electron transfer process in the Cu4 O4 cubanes to form high-valent CuIII and CuIII O. intermediates during the catalysis.

A general electrochemical strategy for the Sandmeyer reaction.

Herein we report a general electrochemical strategy for the Sandmeyer reaction. Using electricity as the driving force, this protocol employs a simple and inexpensive halogen source, such as NBS, CBrCl3, CH2I2, CCl4, LiCl and NaBr for the halogenation of aryl diazonium salts. In addition, we found that these electrochemical reactions could be performed using anilines as the starting material in a one-pot fashion. Furthermore, the practicality of this process was demonstrated in the multigram scale synthesis of aryl halides using highly inexpensive graphite as the electrode. A series of detailed mechanism studies have been performed, including radical clock and radical scavenger study, cyclic voltammetry analysis and in situ electron paramagnetic resonance (EPR) analysis.

Endohedral Metallofullerene as Molecular High Spin Qubit: Diverse Rabi Cycles in Gd2@C79N.

An anisotropic high-spin qubit with long coherence time could scale the quantum system up. It has been proposed that Grover's algorithm can be implemented in such systems. Dimetallic aza[80]fullerenes M2@C79N (M = Y or Gd) possess an unpaired electron located between two metal ions, offering an opportunity to manipulate spin(s) protected in the cage for quantum information processing. Herein, we report the crystallographic determination of Gd2@C79N for the first time. This molecular magnet with a collective high-spin ground state (S = 15/2) generated by strong magnetic coupling (JGd-Rad = 350 ± 20 cm-1) has been unambiguously validated by magnetic susceptibility experiments. Gd2@C79N has quantum coherence and diverse Rabi cycles, allowing arbitrary superposition state manipulation between each adjacent level. The phase memory time reaches 5 µs at 5 K by dynamic decoupling. This molecule fulfills the requirements of Grover's searching algorithm proposed by Leuenberger and Loss.