Ming-Dao Zhang

Optical study on the size effects in BaTiO3 thin films

To study the size effects in ferroelectric thin film, we measured the optical transmittance and Raman spectra in BaTiO3 thin films deposited by the rf-magnetron sputtering technique on fused quartz and (111) Si substrates. A variation in the energy gap and Raman peaks with film thickness and grain size was observed and the possible origin was analyzed.

Structure-property relationship of homochiral and achiral supramolecular isomers obtained by one-pot synthesis.

Two supramolecular isomers, {[Co(L)(OBA)]·H(2)O}(n) (1), {[Co(5)O(2)(L)(2)(OBA)(3)]·7DMF}(n) (2), have been synthesized by one-pot reactions. Compound 1 has a homochiral architecture with low connectivity, and compound 2 is an achiral 3D framework with high 12-connectivity. It is unprecedent to get homochiral and achiral supramolecular isomers by one-pot synthesis.

Chiral 3D/3D hetero-interpenetrating framework with six kinds of helices, 3D polyrotaxane and 2D network via one-pot reaction

Three MOFs including novel architectural features were synthesized via one-pot reaction. Reaction time, temperature and ratio of ligands were found to influence the formation of the three compounds and we obtained conditions to synthesize the three MOFs in purely individual phase directly.

Syntheses, characterizations and properties of five new metal–organic complexes based on flexible ligand 4,4′-(phenylazanediyl)dibenzoic acid

Five new metal–organic frameworks have been synthesized under hydrothermal conditions, in CH3CN–H2O, DMF–CH3CH2OH–H2O and DMA–H2O, namely, [ZnL(bimx)0.5]n (1), {[CoL(4,4′-bipy)]·DMF}n (2), {[CdL(4,4′-bipy)]·DMF}n (3), {[ZnL(bibp)]·DMA·(H2O)2}n (4), {[CoL(bpyb)0.5]·(H2O)2}n (5) (bimx = 1,4-bis(imidazol-1-ylmethyl)benzene, 4,4′-biby = 4,4-pyridine, bibp = 4,4′-bis(imidazol-1-yl)biphenyl, bpyb = 1,4-bis(4-pyridyl)benzene, H2L = 4,4′-(phenylazanediyl)dibenzoic acid. These complexes were characterized by elemental analysis, IR spectroscopy, TG and X-ray single-crystal diffraction. In compounds 1, 2 and 3, the bimx, 4,4′-bipy and L2− anions act as bidentate ligands assembling with metal cations to form two-dimensional (2D) sheets. The sheets are stacked in ABAB fashion and accumulate into a 3D framework. Compound 4 possesses a 3D→3D 4-fold interpenetrating architecture with {65·8} topological net, which is similar to the cds topology. Compound 5 also displays a 3D structure with {44·610·8} topology. The photochemical properties were investigated in the solid state at room temperature. The luminescent properties of compounds 1, 3 and 4 are discussed in detail. The UV-vis absorption spectra of compounds 2 and 5 are tested and discussed. In addition, the magnetic properties of compound 5 also are tested and simply analyzed.

Critical factors influencing the structures and properties of metal–organic frameworks

Metal–organic frameworks (MOFs) have emerged as an important family of compounds that have fascinating structures and diverse applications. But until now, targeted synthesis of MOFs with desired frameworks is still a challenge. In order to appreciate the properties and to design new frameworks, it is necessary to understand how to rationalize the design and synthesis of MOFs from a fundamental perspective. This highlight review will outline the recent advances in this topic from both our and other groups and provide an overview of the different factors influencing the structures of MOFs. These examples illustrate some of the present trends concerning the design of organic ligands and SBUs, coordination assemblies, and experimental conditions.

Two pairs of isomorphism and two 3D metal–organic frameworks based on a star-like ligand tri(4-pyridylphenyl)amine

Six novel metal–organic frameworks (MOFs) have been synthesized in this paper, which are based on a N-centered ligand TPPA, namely, [Cd(TPPA)(fuma)]n (1), {[Zn(TPPA)(suc)]·5(H2O)·DMA}n (2), [Co(TPPA)(bhf)]n (3), [Zn(TPPA)(bhf)]n (4), [Co(TPPA)(oba)]n (5), and [Cd(TPPA)(oba)]n (6), [TPPA = tri(4-pyridylphenyl)amine, H2fuma = fumaric acid, H2suc = succinic acid, H2bhf = 2,2′-bis(4-carboxyphenyl)hexafluoropropane, H2oba = 4,4′-oxybis(benzoic acid)]. Compound 1 reveals a 4-fold interpenetrating 3D framework with AFUQOH topology. Compound 2 reveals a 2-fold interpenetrating 3D network with large void space (up to 37.6%). Compounds 3 and 4 are isomorphic 2D networks. Different from compounds 3 and 4, compounds 5 and 6 show 2D → 3D parallel polycatenation of undulated square layers. In addition, photochemical properties of compounds and the ligands in the solid state have been studied.

Enhanced performance of dye-sensitized solar cells with Y-shaped organic dyes containing di-anchoring groups

Two new Y-shaped D–π–(A)2 type phenothiazine-based dyes (ZJA2 and ZJA3) were designed and synthesized for dye-sensitized solar cells (DSSCs). Compared to the single D–π–A analogue dye ZJA1, the Y-shaped dye with two carboxylic acid anchors was in favour of enhancing the performance of DSSCs. The FTIR spectra revealed that the dye ZJA2 molecules were anchored onto the TiO2 surface by two carboxylic acid anchors, which effectively increased the electron extraction channels. The steady-state emission spectra and time-resolved fluorescence experiments all indicated that the electron injection efficiency of dye ZJA2 was improved by the increased electron extraction channels, thus the Jsc of ZJA2 was greatly improved compared to dye ZJA1. In addition, benzene was used as the π-bridge for linking di-anchoring groups, combined with CDCA, thereby reducing the charge recombination. As a result, the PCE of the DSSC based on ZJA2 (4.55%) was 67% higher than the DSSC based on ZJA1 (2.72%). The Y-shaped D–π–(A)2 type phenothiazine-based dye ZJA3 containing two pyridine anchors was also investigated, and the DSSC based on ZJA3 showed a poor PCE (0.45%) due to the low dye loading.

Picolinic acid as an efficient tridentate anchoring group adsorbing at Lewis acid sites and Brønsted acid sites of the TiO2 surface in dye-sensitized solar cells

We developed a novel efficient tridentate anchoring group which can anchor dyes onto the TiO2 surface via synchronously choosing Lewis acid sites and Bronsted acid sites of TiO2. For the purpose of comparing the traditional carboxylate anchoring group to picolinic acid, two new D–π–A porphyrin dyes (JA1 and JA2) differing only in anchoring groups have been synthesized and applied in dye-sensitized solar cells. Picolinic acid as an anchoring group in the dye JA2 not only extended the scope of the spectral response, but also improved the charge transport properties and enhanced the electron injection efficiency. The PCE of the JA1 based-device (carboxylate as the anchoring group) was 5.76%. The PCE of the JA2 based-device was 7.20%, which increased by 25% compared with JA1. The dye TTR2 was used as a cosensitizer; it would not just make up for the poor absorption of porphyrin dyes in the 470–550 nm range, but also would suppress the main dye aggregation and reduce the charge recombination rate. We found that the picolinic acid anchor was more suitable for the cosensitization system than the carboxylate anchor, for there was almost no competitive adsorption between JA2 and TTR2. The JA2 + TTR2 based-device showed the highest PCE of 8.98% under AM 1.5 G irradiation.

Promising alkoxy-wrapped porphyrins with novel push-pull moieties for dye-sensitized solar cells†‡

Dye-sensitized solar cells (DSSCs) have been considered as very promising third generation solar cells. Porphyrins are promising candidates as highly efficient sensitizers for DSSCs because of their superior light-harvesting ability in the visible region and their mimicking of photosynthesis. This paper focuses on the structure modification of porphyrin dyes for efficient DSSCs, which was based on a rational design using density functional theory (DFT) before the experiment. We synthesized and fully characterized four porphyrin dyes, named ZLD13, ZLD14, ZLD15 and ZLD16. On one hand, we used 5-ethynylthiophene-2-carboxylic acid to replace 4-ethynylbenzoic acid as the electron-withdrawing anchoring group for the first time. Property studies indicate that the aggregation of porphyrin molecules can be sufficiently suppressed via this modification. On the other hand, 4,4′-di(2-thienyl)triphenylamine moiety, which has been proved to be a electron donor group for triarylamine dyes in our previous reports, was introduced to porphyrin dyes, and energy conversion efficiencies (η) were improved by 76% (ZLD15 vs. ZLD13). After the two modifications, the energy conversion efficiency (η) of ZLD16 is comparable with an N719-based reference cell under the same conditions. Enhancement of photovoltaic performances from ZLD13 to ZLD16 is partly due to the decreased dark current and charge recombination rate.

Construction of a series of metal–organic frameworks with a neutral tetradentate ligand and rigid carboxylate co-ligands

The solvothermal reaction of a neutral tetradentate ligand, different bivalent metal salts and two rigid carboxylate co-ligands gave six metal–organic frameworks (MOFs): [Zn(L)(Hbdc)(bdc)0.5]·1.5H2O (1), [Zn2(L)(bdc)2(H2O)]·2H2O (2), [Cd(L)(bdc)(H2O)]·2H2O (3), [Ni(L)(bdc)(H2O)]·H2O (4), [Co3(L)(btc)2(H2O)4] (5), [Zn3(L)(btc)2(H2O)4] (6) (L = 1,1′-oxybis[3,5-dipyridine]-benzene, H2bdc = 1,4-benzenedicarboxylate, H3btc = 1,3,5-benzenetricarboxylate). Compounds 1 and 2 have been co-crystallized in a one-pot reaction. In compound 1, L and H2bdc ligands link Zn centers to generate a two-dimensional (2D) sheet structure which is further connected by intermolecular hydrogen bonds to form a 3-fold interpenetrating 3D fsc-3,4-C2/c array. Single crystal X-ray diffraction analysis reveals that compound 2 features a 3D self-interpenetrated network with {4·6·83·10}{4·63·82}{64·82} topology. For compounds 3 and 4, the binuclear metal secondary building unit (SBU) assembles with mixed ligands, L and H2bdc, to construct a 3D α-Po structure. Compounds 5 and 6 are isostructural and show 3-fold interpenetrated pte/Cmmm->P2/c structures.