Seven new secondary metabolites isolated from roots of Lespedeza bicolor.

Chemical investigation of a methanol extract obtained from the roots of Lespedeza bicolor identified one new pterocarpene (1), three new pterocarpans (2-4), and three new arylbenzofurans (5-7), and two known compounds (8 and 9). Their structures were determined by interpretations obtained from combined UV, NMR, and HRTOFMS spectroscopic data. Furthermore, the absolute configurations of compounds 2 and 3 were established by the combination of electronic circular dichroism (ECD) calculations and NMR calculations with DP4+ probability analysis. All isolated compounds (1-9) were evaluated for cytotoxicity against the human lung carcinoma cell line A549 and the human hepatoma cell line Huh-7. Compound 4 showed antiproliferative activity against A549 cell line with IC50 value of 24.9 µM. Furthermore, compound 9 exhibited cytotoxicity against Huh-7 cell line with IC50 value of 68.7 µM.

Hexagonal Carbon Nanoplates Decorated with Layer-Engineered MoS2: High-Performance Cathode Materials for Zinc-Ion Batteries.

Hexagonal carbon nanoplates bearing MoS2 (HCN@MoS2) were synthesized using two-dimensional (2D) microporous organic polymers as templating materials. The layer number of MoS2 in HCN@MoS2 and the 2D morphology of composites were critical factors to achieve high-performance cathode materials for aqueous zinc-ion batteries. The best cathode performance was obtained with HCN@MoS2 bearing 2-3 layered MoS2 (HCN@MoS2-2), showing excellent discharge capacities of 602 mAh/g (@50 mA/g), 498 mAh/g (@0.1 A/g), and 328 mAh/g (@1 A/g). The promising electrochemical performance of HCN@MoS2-2 is attributable to the facilitated insertion of zinc ions into 2-3 layered MoS2 due to the reduced lattice energy and the efficient electrochemical utilization of composite materials.

Room-Temperature Synthesis of a Hollow Microporous Organic Polymer Bearing Activated Alkyne IR Probes for Nonradical Thiol-yne Click-Based Post-Functionalization.

This work shows that hollow microporous organic polymer (H-MOP-A) with activated internal alkynes as IR probes can be prepared by template synthesis based on acyl Sonogashira-Hagihara coupling at room temperature. The H-MOP-A is a versatile platform in the main chain PSM based on nonradical thiol-yne click reaction. Moreover, an IR peak of internal alkynes in the H-MOP-A is very intense and could be utilized in the monitoring of thiol-yne click-based main chain PSM. The functionalized H-MOP-A with carboxylic acids (H-MOP-CA) showed efficient adsorption toward Ag+ ions. The resultant H-MOP-CA-Ag showed excellent performance in the CO2 fixation to α-alkylidene cyclic compounds.

Vibrational Energy Flow in the Uracil-H2O Complexes.

In the uracil-H2O complex, the vibrational energy initially stored in the OH(v = 1) stretch efficiently transfers to the first overtone-bending mode under a near-resonant condition. The relaxation of the overtone vibration redistributes its energy to uracil and the two hydrogen bonds in the intermolecular zone, which consists of the OH bond and the bonds between nearby C, N, O, and H atoms of uracil. The uracil NH bond and the hydrogen bond it formed with the H2O molecule, N-H···O, store the major portion of the energy released by the relaxing bending mode, thus forming a localized hot band in the intermolecular zone. Energy transfer to the bonds beyond the zone is found to be not significant. The excited uracil NH is found to transfer its energy to the bending mode, thus indicating that the hydrogen bond of N-H···O is the principal energy pathway in both directions. In the presence of efficient near-resonant energy transfer pathways, the time evolution of the centers of mass distance shows the phenomenon of beats. One global and two different local minima energy structures are considered. The results of energy transfer do not differ significantly, suggesting that the two hydrogen bonds in all three structures have similar contributions to the energy transfer.

Broadband white-light emission from supramolecular piperazinium-based lead halide perovskites linked by hydrogen bonds.

We demonstrate white-light emission using lead halide perovskites: (pip)2PbBr6 (pip = piperazine), (pip)2Pb4Cl12, (1mpz)2PbBr6 (1mpz = 1-methylpiperazine), and (2,5-dmpz)0.5PbBr3·2((CH3)2SO) (2,5-dmpz = trans-2,5-dimethylpiperazine, abbreviated as (2,5-dmpz)0.5PbBr3), in which the inorganic frameworks were connected by piperazinium dications through hydrogen bonds, forming a three-dimensional supramolecular network. From single-crystal X-ray diffraction measurements and Raman spectroscopy, we identified the crystal structures and local environmental vibrational modes in the inorganic framework, finding that (pip)2PbBr6 crystallized in the centrosymmetric orthorhombic space group Pnnm, whereas (pip)2Pb4Cl12 crystallized in the trigonal/rhombohedral space group R3. The zero-dimensional (1mpz)2PbBr6 structure crystallized in the centrosymmetric monoclinic space group P2/n, whereas the [PbBr6]4- octahedron was separated by a 1-methylpiperazine dication. (2,5-dmpz)0.5PbBr3·2((CH3)2SO) contained half a cation, which was completed by inversion symmetry, along with two dimethyl sulfoxide solvent molecules that crystallized in the monoclinic space group P21/c. Among the perovskites, (2,5-dmpz)0.5PbBr3·2((CH3)2SO) exhibited the longest carrier lifetime (42 ns), the lowest band gap (2.34 eV), and the highest photoluminescence quantum yield (58.02%). This is because it forms a 1D corner-sharing structure and has localized electronic states near the conduction band minimum, which contributes to the high photoluminescence quantum yield and white-light emission.

Morphology engineering of a Suzuki coupling-based microporous organic polymer (MOP) using a Sonogashira coupling-based MOP for enhanced nitrophenol sensing in water.

The morphology of a Suzuki coupling-based microporous organic polymer (SUM) was controlled by the use of a Sonogashira coupling-based microporous organic polymer (SOM). The template synthesis resulted in water compatible and hollow SOM@SUM materials bearing tetraphenylethylene moieties (H-SOM@SUM-T), which showed aggregation-induced emission and promising sensing performance towards nitrophenols in water.

Effective modulation of intramolecular ferromagnetic interaction of diradicals by functionalization of cross-conjugated coupler.

Cross-conjugated molecules are an interesting class of conjugated systems possessing a spatially separated HOMO and LUMO. Most previous studies have taken advantage of this property by using it in organic semiconductor applications. Herein, we undertake a new investigation on the use of this type of molecule, in particular benzo[1,2-d;4,5-d']bisoxazole (BBO), as a coupler for organic diradicals. BBO has two sites available for adding a substituent and a spin center (SC) which are along its 4,8- and 2,6-axes. Functionalizations using electron donating (ED) and electron withdrawing (EW) groups were imposed to tune its FMOs and it was found that the longer 2,6-axis is an ideal site with a broader LUMO range via substituent effects. Diradicalization of these BBOs using nitronyl nitroxide (NN) and nitroxide (NO) as SCs was done using the remaining available axis. The calculated J values are linearly dependent on the LUMO energy of the coupler, but with 4,8-NH2-2,6-SC as an outlier. This exceptional case is related to 4,8-NH2-2,6-SC having the lowest BBO-NN dihedral angle. Moreover, the diradicals 4,8-X-2,6-SC (with X = H, NH2, CH3) have higher J values than 2,6-X-4,8-SC (with X = H, NH2, CH3), which is counterintuitive because the latter have a shorter coupling path. These diradicals are positioned to the right of the intersection of their trend lines, which implies that diradicals with LUMO values to the right of this intersection have the tendency to attain J values that are higher than those diradicals with a shorter coupling path. 4,8-NH2-2,6-SC even surpasses the projected JMax values which we associate with the highest attainable J values due to LUMO tuning via substituent effects. These results provide useful insights, especially into the interplay between the LUMO and the dihedral angle and how these affect magnetism in diradicals. In conclusion, we found that BBO can be a good candidate as an effective coupler for diradicals with tunable J values via incorporation of ED and EW groups. This first approach to studying the application of cross-conjugated molecules as couplers also paves the way for new candidates for the development of more effective diradical systems.

Network-controlled unique reactivities of carbonyl groups in hollow and microporous organic polymer.

Hollow and microporous organic network bearing alkynone moieties was prepared via carbonylative Sonogashira coupling. The carbonyl groups in the network showed unusual chemical reactivities, compared with those of a model alkynone compound. The observed differences between the reactivities of alkynones in the molecule and in the network were analyzed based on the "network effect".

In Situ Water-Compatible Polymer Entrapment: A Strategy for Transferring Superhydrophobic Microporous Organic Polymers to Water.

Microporous organic polymer nanoparticles bearing tetraphenylethylene moieties (MOPTs) were prepared in the presence of poly(vinylpyrrolidone) (PVP). The PVP was entrapped into the microporous network of MOPT to form MOPT-P and played the roles of size control, porosity enhancement, and surface property management. MOPT materials without PVP showed superhydrophobicity with a water contact angle of 151°. In comparison, the MOPT-P showed excellent water compatibility. Moreover, due to the aggregation-induced emission property of tetraphenylethylene moieties, the MOPT-P showed emission and excellent emission-based sensing of nitrophenols in water with Ksv values in the range of 1.26 × 104 ∼ 3.37 × 104 M-1. It is noteworthy that the MOPT-P used water only as a sensing medium and did not require additional organic solvents to enhance water dispersibility of materials. The MOPT-P could be recovered and reused for the sensing at least five times.

Calix[n]triazoles and Related Conformational Studies.

Calix[n]triazoles are developed as new derivatives in the calixarene family. Calixtriazole compounds 2-4 are synthesized using an iterative convergent strategy including an inter-/intramolecular copper(I)-catalyzed azide-alkyne cycloaddition reaction. Solid-state structures are clearly refined to give 1,2-alternate and partial cone conformations for calix[4]triazole and calix[5]triazole, respectively. Theoretical studies based on density functional theory (DFT) calculations indicated that intermolecular interactions are crucial in determining the conformers of the crystals, and the most stable conformers of calix[4]triazole, calix[5]triazole, and calix[6]triazole in the monomeric forms are 1,3-alternate, 1,3-alternate, and 1,3,5-alternate, respectively.

Size-Dependent Level Alignment between Rutile and Anatase TiO2 Nanoparticles: Implications for Photocatalysis.

Motivated by the enormous importance of nanoscale TiO2 in a wide range of photocatalytic applications and the ill-understood high activity of the commercial nano-TiO2 photocatalysts, we provide a predictive map of how the anatase-rutile level alignment varies from the smallest nanoparticles (NPs) to the bulk. Specifically, we compute the size dependence of the energies of vacuum-referenced electronic levels in a range of realistically structured rutile and anatase TiO2 NPs employing accurate all-electron density functional calculations. In agreement with most recent work, a staggered type II anatase level alignment is predicted for the bulk phases, which we further find to persist into the regime of large NPs. We predict that other level alignments will emerge when the diameter of the TiO2 NPs is reduced below ∼15 nm. Our results suggest how experiment could test the widely debated importance of the bulk-like type II anatase level alignment for enhanced photoactivity of nano-TiO2.

When Anatase Nanoparticles Become Bulklike: Properties of Realistic TiO2 Nanoparticles in the 1-6 nm Size Range from All Electron Relativistic Density Functional Theory Based Calculations.

All electron relativistic density functional theory (DFT) based calculations using numerical atom-centered orbitals have been carried out to explore the relative stability, atomic, and electronic structure of a series of stoichiometric TiO2 anatase nanoparticles explicitly containing up to 1365 atoms as a function of size and morphology. The nanoparticles under scrutiny exhibit octahedral or truncated octahedral structures and span the 1-6 nm diameter size range. Initial structures were obtained using the Wulff construction, thus exhibiting the most stable (101) and (001) anatase surfaces. Final structures were obtained from geometry optimization with full relaxation of all structural parameters using both generalized gradient approximation (GGA) and hybrid density functionals. Results show that, for nanoparticles of a similar size, octahedral and truncated octahedral morphologies have comparable energetic stabilities. The electronic structure properties exhibit a clear trend converging to the bulk values as the size of the nanoparticles increases but with a marked influence of the density functional employed. Our results suggest that electronic structure properties, and hence reactivity, for the largest anatase nanoparticles considered in this study will be similar to those exhibited by even larger mesoscale particles or by bulk systems. Finally, we present compelling evidence that anatase nanoparticles become effectively bulklike when reaching a size of ∼20 nm diameter.

Single oxygen vacancies of (TiO2)35 as a prototype reduced nanoparticle: implication for photocatalytic activity.

Titanium dioxide (TiO2), as a semiconductor metal oxide, has been one of the most popular materials studied in the field of photocatalysis. In the present study, the properties of single oxygen vacancies of (TiO2)35, a prototype of an anatase nanoparticle, were investigated by DFT calculations. (TiO2)35 is the minimum sized model (∼2 nm) for a bipyramidal nanoparticle with anatase phase and eight {101} facets. All the available oxygen vacancies at various sites according to position, coordination number, and distance from the center atom were examined. The geometric, energetic and electronic properties of the reduced TiO2 clusters were analyzed by hybrid DFT functionals with different Hartree-Fock exchange ratios (0, 12.5 and 25%). It was found that the structure of pristine (TiO2)35 is somewhat different from the bulk lattice, with a relatively high surface to volume ratio. Moreover, the particular highly (three)-coordinated oxygen atom is energetically the most favorable for oxygen vacancy formation from the nanoparticle mainly due to its substantially high relaxation energy. TiO2 nanoparticles have low oxygen vacancy formation energy and narrow band gap because of their defect states, and can be utilized as an efficient photocatalyst material.

Effect of Size and Structure on the Ground-State and Excited-State Electronic Structure of TiO2 Nanoparticles.

We investigated the influence of size and structure on the electronic structure of TiO2 nanoparticles 0.5-3.2 nm in diameter, in both vacuum and water, using density functional theory (DFT) calculations. Specifically, we tracked the optical and electronic energy gap of a set of (TiO2)n nanoparticles ranging from small non-bulklike clusters with n = 4, 8, and 16, to larger nanoparticles derived from the anatase bulk crystal with n = 35 and 84. As the difference between these two energy gaps (the exciton binding energy) becomes negligible in the bulk, this magnitude provides an indicator of the bulklike character of the electronic structure of the nanoparticles under study. Extrapolating our results to larger sizes, we obtain a rough estimate of the nanoparticle size at which the electronic structure will begin to be effectively bulklike. Our results generally confirmed that the electronic structure of the nanoparticle ground state and excited state has a more pronounced structure dependency than size dependency within a size range of 0.5-1.5 nm. We also showed that the thermodynamic preference for the photocatalytic species is the first S1 exciton. This S1 exciton is stable under vacuum but may evolve to free charge carriers upon structural relaxation in an aqueous environment for particles 0.5-1.5 nm in size studied in the present article. An analysis of ionization potentials and electron affinities, relative to the standard reduction potential for the water splitting half-reactions, revealed the importance of considering the structural relaxation in the excited states and the presence of water for assessing the thermodynamic conditions for photocatalytic water splitting.

Mitochondria-Targeted Reaction-Based Fluorescent Probe for Hydrogen Sulfide.

In this study, we developed a turn-on mitochondria-targeting hydrogen sulfide, "probe 1", based on the selective thiolysis of 7-nitro-1,2,3-benzoxadiazole amine moiety attached to the piperazine-based naphthalimide scaffold. Probe 1 exhibited excellent properties with 68-fold fluorescence enhancement, a low detection limit (2.46 µM), a low cytotoxicity, and a good selectivity toward hydrogen sulfide. The success of intracellular imaging indicated that probe 1 could be used in further applications for the investigation of biological functions and pathological roles of H2S in living systems.

Performance of a modified hybrid functional in the simultaneous description of stoichiometric and reduced TiO2 polymorphs.

Conventional density functionals with either the local density approximation (LDA) or the generalized gradient approximation (GGA) form of the exchange-correlation potential fail to describe the electronic structure of a large number of metal oxides. Both the LDA and the GGA grossly underestimate the band gaps of these materials which severely affect the description of oxygen vacancy point defect states in reduced samples. To find a pragmatic approach to simultaneously and accurately describe the atomic and electronic structures of the most common TiO2 polymorphs, we explore the effect of the percentage of exact, non-local, Fock exchange on the electronic structure of stoichiometric rutile and anatase. From these results, a modified hybrid functional is proposed to properly describe the atomic structures, formation enthalpies and electronic structures of rutile and anatase and, at the same time, the results of reduced samples are also in good agreement with the available experimental results. The present approach can be safely used to accurately describe numerous TiO2 based materials containing defects or realistic nanoparticles for which the required large unit cells or system sizes hinder the use of GW related techniques.

Effect of Hartree-Fock exact exchange on intramolecular magnetic coupling constants of organic diradicals.

The intramolecular magnetic coupling constant (J) of diradical systems linked with five- or six-membered aromatic rings was calculated to obtain the scaling factor (experimental J/calculated J ratio) for various density functional theory (DFT) functionals. Scaling factors of group A (PBE, TPSSh, B3LYP, B97-1, X3LYP, PBE0, and BH&HLYP) and B (M06-L, M06, M06-2X, and M06-HF) were shown to decrease as the amount of Hartree-Fock exact exchange (HFx) increases, in other words, overestimation of calculated J becomes more severe as the HFx increases. We further investigated the effect of HFx fraction of DFT functional on J value, spin contamination, and spin density distributions by comparing the B3LYP analogues containing different amount of HFx. It was revealed that spin contamination and spin densities at each atom increases as the HFx increases. Above all, newly developed BLYP-5 functional, which has 5% of HFx, was found to have the scaling factor of 1.029, indicating that calculated J values are very close to that of experimental values without scaling. BLYP-5 has potential to be utilized for accurate evaluation of intramolecular magnetic coupling constant (J) of diradicals linked by five- or six-membered aromatic ring couplers.

Simple but useful scheme toward understanding of intramolecular magnetic interactions: benzene-bridged oxoverdazyl diradicals.

It has recently been shown that the types of intramolecular magnetic interactions of diradical systems can be changed by the types of radical group: syn-group (or α-group) and anti-group (or ß-group). The aim of this study is to establish a useful scheme to understand and explain the intramolecular magnetic interactions in diradical systems regardless of radical groups and the topology of a coupler. We investigated the intramolecular magnetic coupling constant (J) of six oxoverdazyl diradicals (i-vi) coupled with a benzene ring based on the unrestricted DFT calculations. On the basis of our results, we devised a simple but useful scheme by combining the spin alternation rule and the concept of radical group classification. Consequently, it was found that the calculated J values and plots of spin density distributions were consistent with our proposed scheme. In addition, we discussed the closed-shell singlet (CS) state and the dihedral angle effect on J values in detail to comprehensively understand the magnetic interactions of diradical systems. Our scheme can provide the basic framework to design future organic high-spin molecules and organic magnetic materials.

Organic magnetic diradicals (radical-coupler-radical): standardization of couplers for strong ferromagnetism.

The intramolecular magnetic coupling constant (J) values of sets of diradicals linked to bis-DTDA, OVER, and NN radicals (DTDA, OVER, and NN groups) through an aromatic coupler were studied by unrestricted density functional theory calculations (UB3LYP/6-311++G(d,p)). Among 15 aromatic couplers, 9 compounds with an odd number of carbon atoms along its spin coupling path were found to interact ferromagnetically upon coupling with bisradicals while the other 6 couplers with an even number of carbon atoms along its spin coupling path give rise to antiferromagnetic coupling. The overall trends in the strength of magnetic interactions of aromatic couplers were preserved for DTDA, OVER, and NN groups so that the trend can be utilized as an index for the magnetic strength of a given coupler. It was found that the differences in the nucleus-independent chemical shift (NICS), bond order of connecting bonds, and Mulliken atomic spin density at connected atoms between triplet and BS states are closely related to the intramolecular magnetic behavior. 2,4- and 2,5-phosphole couplers exhibit the strongest intramolecular ferromagnetic and antiferromagnetic interactions among 15 aromatic couplers when linked to diverse bisradicals.