Qian Duan

Hemi-salen aluminum catalysts bearing N, N, O-tridentate type binaphthyl-Schiff-base ligands for the living ring-opening polymerisation of lactide

Four hemi-salen aluminum complexes based on tridentate N, N, O-type binaphthyl-Schiff-base derivatives (1: R = iPr; R1 = H; 2: R = iPr; R1 = Cl; 3: R = 2-adamantyl; R1 = H; 4: R = 2-adamantyl; R1 = tBu) were prepared. These complexes were characterized by 1H, 13C NMR spectroscopy and elemental analysis, these four complexes were employed for ring-opening polymerisation of L-lactide and rac-lactide. Complex 2, which was based on pro-ligand L2 with smaller steric hindrance and electron-withdrawing substituents, displayed the highest activity for ROP of L-lactide among these complexes, and complex 4, which was supported by pro-ligand L4 with the biggest steric hindrance, showed the highest stereoselectivity for the ROP of rac-lactide with partially isotactic polylactide with a Pm of 0.65. Kinetic studies revealed the ROP of L-lactide initiated by complex 3 had first-order dependency on [LA] as well as [Al].

Origin of the responsivity characteristics of Au/ZnO/MgZnO and Au/MgZnO/ZnO structured ultraviolet photodetectors

We report on the ultraviolet photodetectors based on the MgZnO/ZnO and ZnO/MgZnO double-layer films prepared by magnetron sputtering method. The spectral response shows only one responsivity peak in the 1.0 and 1.5 h photodetectors (denoted by the deposition time of one layer of the films) and two peaks in the 0.5 h photodetectors. To our surprise, the Au/MgZnO/ZnO photodetectors have larger responsivity than that of the Au/ZnO/MgZnO ones. A physical mechanism focused on depletion width is given to explain the above results.

Di/mono-nuclear iron(I)/(II) complexes as functional models for the 2Fe2S subunit and distal Fe moiety of the active site of [FeFe] hydrogenases: protonations, molecular structures and electrochemical properties

Di/mono-nuclear iron(I)/(II) complexes containing conjugated and electron-withdrawing S-to-S linkers, [{(μ-S)(2)(C(4)N(2)H(2))}Fe(2)(CO)(6)] (1), [{(μ-S)(2)(C(4)N(2)H(2))}Fe(2)(CO)(5)(PMe(3))] (1P), and [{(μ-S)(2)(C(4)N(2)H(2))}Fe(CO)(2)(PMe(3))(2)] (2) were prepared as biomimetic models for the 2Fe2S subunit and distal Fe moiety of the active site of [FeFe] hydrogenases. The N atoms in the heterocyclic pyrazines of 1 and 2 were protonated in the presence of proton acid to generate one and two hydrides, [1(NH)](+) CF(3)SO(3)(-), [2(NH)](+) CF(3)SO(3)(-), and [2(NH)(2)](2+) (CF(3)SO(3)(-))(2), respectively. The protonation processes were evidenced by in situ IR and NMR spectroscopy. The molecular structures of the protonated species [1(NH)](+) CF(3)SO(3)(-) and [2(NH)(2)](2+) (CF(3)SO(3)(-))(2) together with their originating complexes and , and the mono-PMe(3) substituted diiron complex were identified by X-ray crystallography. The IR and single-crystal analysis data all suggested that the electron-withdrawing bridge, pyrazine, led to decreased electron density at the Fe centers of the model complexes, which was consistent with the electrochemical studies. The cyclic voltammograms indicated that complex exhibited a low primary reduction potential at -1.17 V vs. Fc-Fc(+) with a 270 mV positive shift compared with that of the benzene-1,2-dithiolate (bdt) bridged analogue [(μ-bdt)Fe(2)(CO)(6)]. Under the weak acid conditions, complexes 1 and 2 could electrochemically catalyze the proton reduction. More interestingly, the mononuclear ferrous complex 2 showed two catalytic peaks during the formation of hydrogen, confirming its potential as a catalyst for hydrogen production.

Preparation of biocompatible, biodegradable and sustainable polylactides catalyzed by aluminum complexes bearing unsymmetrical dinaphthalene-imine derivatives via ring-opening polymerization of lactides

A number of half-salen aluminum complexes bearing unsymmetrical [ONN]-type ligands were prepared from tridentate dinaphthalene-imine derivatives. These complexes were characterized by 1H and 13C NMR spectroscopy, elemental analysis and single crystal X-ray diffraction analysis. These complexes were employed for rac-lactide and L-lactide polymerization. Upon activation with isopropanol, complex (S)-B6 (R1 = R2 = R4 = H; R3 = F) showed the highest activity (a monomer conversion of 94.6%) amid these aluminum complexes for the ring-opening polymerization of L-lactide; and complex (S)-B2 (R1 = R2 = R3 = H; R4 = tBu) showed the highest stereoselectivity for the ring-opening polymerization of rac-lactide, obtaining a polylactide (PLA) with a Pm of 0.69. The polymerization kinetics utilizing (S)-B6 as a catalyst were researched in detail. The data on the polymerization kinetics revealed that the rate of polymerization was first-order with respect to the monomer and the catalyst. There was a linear relationship between the L-lactide conversion and the number-average molecular weight of PLA.

Ring-opening polymerization of lactide using chiral salen aluminum complexes as initiators: high productivity and stereoselectivity

A family of aluminum complexes bearing chiral salen ligands derived from (R,R)-1,2-diammoniumcyclohexane mono-(+)-tartrate salt and modified by salicylaldehyde were prepared. The complexes were characterized by 1H, 13C NMR and elemental analysis. These complexes were used as initiators for the ring-opening polymerization (ROP) of L-lactide and rac-lactide. Complex 2 (R1 = R2 = Cl) showed the highest activity among these complexes for the ROP of L-lactide, and complex 3 (R1 = tBu, R2 = Cl) showed the highest stereoselectivity for the ROP of rac-lactide with enriched isotactic polylactide with a Pm of 0.91. The kinetic data of the polymerization employing complex 3 as initiator indicated that the polymeric rate was first-order in both lactide and in initiator.

High-performance ultraviolet photodetectors based on ZnO/Au/ZnO sandwich structure

We developed sandwich ultraviolet photodetectors by a radio frequency magnetron sputtering method. As expected, the performances of the optimized ZnO/Au/ZnO sandwich photodetectors are much better than that of a metal-semiconductor-metal structure through combing high responsivity (enlarged ~60 times) and low dark current (reduced by more than two orders of magnitudes). To investigate the above phenomena, simulations of electric-field intensity distribution in the two structured photodetectors were performed using the ANSYS software. A proposed physical mechanism is used to explain the above results, which agree well with the simulations.

Responsivity enhancement of ZnO/Pt/MgZnO/SiO2 and MgZnO/Pt/ZnO/SiO2 structured ultraviolet detectors by surface plasmons in Pt nanoparticles

The structured (ZnO/Pt/MgZnO/SiO2) ultraviolet detector was fabricated and demonstrated to investigate how metallic nanoparticles localized surface plasmons contribute when the two different dielectrics surrounded simultaneously. After sandwiching the Pt nanoparticles between the double layers of MgZnO and ZnO, the extinction was increased largely. Meanwhile, by examining the dependence of MgZnO and ZnO peak responsivity enhancement ratio, we found that MgZnO was significantly larger than ZnO. The interpretation by considering is that the localized surface plasmons of energy match with MgZnO which is superior to ZnO. In order to validate this conclusion and make it more accurate, we also fabricated the MgZnO/Pt/ZnO/SiO2 structure. Our work suggests that rational integration of double-layer and metal nanoparticles is a viable approach to perceive localized surface plasmons with double-layer ultraviolet detectors, which may help to advance optoelectronic devices.

Exploring the geometrical structures of X©BnHnm [(X, m) = (B, +1), (C, +2) for n = 5; (X, m) = (Be, 0), (B, +1) for n = 6] by an electronic method

A series of singlet and triplet wheel-type clusters obtained through an electronic method, i.e., adding two and four electrons into X©BnHnm [(X, m) = (B, +1), (C, +2) for n = 5; (X, m) = (Be, 0), (B, +1) for n = 6], have been studied theoretically. With the increase of the number of electrons, the sizes of peripheral boron rings tend to decrease due to the increase of negative charges on the boron rings. The results of the kinetic stability and the electronic stability suggest that the triplet C©B5H5 and singlet Be©B6H6 are stable and may be detected experimentally. Nucleus-independent chemical shift and molecular orbital analysis reveal that some wheel-type clusters with the planar ring possess aromaticity properties that are attributed to the delocalized π electrons conforming to the Huckel rule, i.e. 4n + 2 for singlets or 4n for triplets. These findings from this work are significant for designing novel wheel-type clusters.

The employment of a hydrophilic tris(morpholino)phosphine ligand in diiron propane-1,3-dithiolate complexes for potentially water-soluble iron-only hydrogenase active-site mimics

A tris(morpholino)phosphine (TMP) ligand was introduced into the diiron dithiolate complexes in order to improve the hydro- and protophilicity of the iron-only hydrogenase active site models. Mono- and di-TMP substituted diiron complexes, (μ-pdt)[Fe(CO)3][Fe(CO)2(TMP)] (2, pdt = 1,3-propanedithiolato) and (μ-pdt) [Fe(CO)2(TMP)]2 (3), were synthesized and spectroscopically characterized. The coordination configuration of 3 was determined by single X-ray analysis. Temperature-dependent 1H and 31P NMR spectroscopy studies provided insight into the interconversion of the irondithiacyclohexane ring and the rotation of the [Fe(CO)2PR3] moieties for 2 and 3 in solution. The electrochemical properties of 2 and 3 were investigated in pure CH3CN and CH3CN–H2O mixtures in the absence and presence of acetic acid. Hydrogen production and the dependence of current on acid concentration indicated that complexes 2 and 3 exhibited electrocatalytic activities for proton reduction in both pure and H2O-containing CH3CN solutions. The current sensitivities, i.e., electrocatalytic activities, were demonstrated to be greater in CH3CN–H2O mixtures than in pure CH3CN. The most effective electrocatalytic activities of 2 and 3 were observed with 10% added water.

An artificial [FeFe]-hydrogenase mimic with organic chromophore-linked thiolate bridges for the photochemical production of hydrogen

An artificial [FeFe]-hydrogenase ([FeFe]-H2ase) mimic 3II, consisting of dual organic chromophores covalently assembled to the [Fe2S2] active site, was constructed for light-driven hydrogen evolution. The structural conformation of synthetic photocatalyst was characterized crystallographically and spectroscopically. The photo-induced intramolecular electron transfer was evidently demonstrated by the combination of electrochemical, steady-state, and transient absorption spectroscopic studies. Finally, a remarkable activity was obtained in the present photocatalytic system, indicating the covalent incorporation of photosensitizer and catalytic center as a promising strategy to construct inexpensive, easily accessible [FeFe]-H2ase model photocatalysts.