Yuwei Dong

Assembly of one-, two-, and three-dimensional Ln(III) complexes constructed from a novel asymmetric tricarboxylic acid: synthesis, structure, photoluminescence and tunable white-light emission

By reacting an asymmetric semi-rigid V-shaped linker H3dpob (H3dpob = 3-(2′3′-dicarboxylphenoxy)benzoic acid) and Ln(NO3)3·6H2O, nine novel Ln-based luminescent materials, from 1D to 3D, namely {[Eu(dpob)(phen)]·H2O}n (1), {[Ln(Hdpob)(ox)0.5(H2O)2]}n (Ln = Eu(2), Sm(3), Gd(4), Tb(5)), {[Eu(dpob)(H2O)2]·0.5H2O}n (6), and {[Ln(dpob)(H2O)2]·mH2O}n (Ln = Eu(7), Gd(8), Tb(9), m = 0.5 for 7 and 9; m = 1 for 8) (phen = 1,10-phenanthroline; H2ox = oxalic acid) have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction, infrared (IR) spectroscopy, elemental analysis, and PXRD. The crystal structures of 1–9 indicate that the coordination modes and coordination configuration of the H3dpob ligand play critical roles in the formation of the lanthanide architectures. Complexes 1–5 display multiple structures from double-stranded 1D chains to 4-connected 2D layers, through [Eu2(CO2)4] or [Eu2(CO2)2] dinuclear units with different auxiliary ligands. Complexes 6 and 7 are genuine supramolecular isomers which are induced by the concentration effect. 6 possesses a 2D kgd network with a Schlafli symbol of (43)2(46·66·83) built from 6-connected [Eu2(CO2)2] units and 3-connected H3dpob, which further connects to a (3,8)-connected tfz-d topology through O–H⋯O hydrogen bonds. 7 displays a 3D (3,6)-connected rtl network with the Schlafli symbol (4·62)2(42·610·83). Eu complexes 1, 2, 6, and 7 as well as Tb complexes 5 and 9 could provide intense and bright characteristic 5D0 → 7FJ/5D4 → 7FJ red/green luminescence under UV excitation in the solid state at 298 K and 77 K. The calculated singlet and triplet energies of H3dpob as well as phen and H2ox ligands indicate that these ligands act as antenna chromophores that are able to efficiently absorb and transfer energy to Ln(III) ions. In complexes 1, 2 and 5, ligand-to-metal energy transfer processes could occur in mixed ligands. However, these processes occurred in a single H3dpob ligand in complexes 6 and 7. With careful adjustment of the relative concentration of the lanthanide ions and by varying the excitation wavelengths of {[Gd0.92Eu0.04Tb0.04(dpob)(H2O)2]·0.5H2O}n (10), tunable yellow (CIE coordinate: 0.51, 0.40) to white-light (CIE coordinate: 0.33, 0.34) emission has been obtained.

Tunable Luminescence and Application in Dye-Sensitized Solar Cells of Zn(II)/Hg(II) Complexes: Methyl Substitution-Induced Supramolecular Structures Based on (E)-N-(6-Methoxypyridin-2-ylmethylene)arylamine Derivatives

Using Schiff-base ligands (E)-N-(6-methoxypyridin-2-yl)(CH═NAr) (where Ar = C6H5, L1; 2-MeC6H4, L2; 2,4,6-Me3C6H2, L3), six Zn(II)/Hg(II) complexes, namely, [ZnL1Cl2] (Zn1), [HgL1Cl2] (Hg1), [ZnL2Cl2] (Zn2), [HgL2Cl2] (Hg2), [ZnL3Cl2] (Zn3), and [HgL3Cl2] (Hg3) have been synthesized under solvothermal conditions. The structures of six complexes have been established by X-ray single-crystal analysis and further physically characterized by EA, FT-IR, (1)H NMR, and ESI-MS. The crystal structures of these complexes indicate that noncovalent interactions, such as hydrogen bonds, C-H···Cl, and π···π stacking, play essential roles in constructing the resulting supramolecular structures (1D for Hg3; 2D for Zn2, Hg2; 3D for Zn1, Hg1, and Zn3). Upon irradiation with UV light, the emission of complexes Zn1-Zn3 and Hg1-Hg3 could be finely tuned from green (480-540 nm) in the solid state to blue (402-425 nm) in acetonitrile solution. It showed that the ligand and metal cation can influence the structures and luminescence properties of complexes such as emission intensities and maximum wavelengths. Since these ligands and complexes could compensate for the absorption of N719 in the low-wavelength region of the visible spectrum and reduce charge recombination of the injected electron, the ligands L1-L3 and complexes Zn3/Hg3 were employed to prepare cosensitized dye-sensitized solar cells devices for investigating the influences of the electron-donating group and coordination on the DSSCs performance. Compared to DSSCs only being sensitized by N719, these prepared ligands and complexes chosen to cosensitize N719 in solar cell do enhanced its performance by 11-41%. In particular, a DSSC using L3 as cosensitizer displays better photovoltaic performance with a short circuit current density of 18.18 mA cm(-2), corresponding to a conversion efficiency of 7.25%. It is much higher than that for DSSCs only sensitized by N719 (5.14%).

Structure variations of a series of lanthanide complexes constructed from quinoline carboxylate ligands: photoluminescent properties and PMMA matrix doping

A series of lanthanide complexes with formulae {[KEu(Hqlc)(qlc)(H2O)6(OH)]2+·2Cl−}n (1·Eu), {[Eu(qlc)2(phen)(H2O)2]+·Cl−}·CH3CN (2·Eu), [Eu(qlc)2(phen)(NO3)]·H2O (3·Eu), [Ln(qlc)2(H2O)4]·(qlc)·(H2O) (Ln = Eu(4·Eu), Sm(5·Sm), Gd(6·Gd), Tb(7·Tb), Dy(8·Dy), Ho(9·Ho)) (Hqlc = quinoline-3-carboxylic acid, phen = 1,10-phenanthrolin) are synthesized under solvo(hydro)thermal conditions and characterized by single-crystal X-ray diffraction, infrared spectra, elemental analysis, and powder X-ray diffraction. Complex 1 exhibits two-dimensional (6,3)-connected hcb networks and possesses a stable structure through typical O/C–H⋯Cl intermolecular hydrogen bonds. Complexes 2–4 display three diverse dimer structures, due to the synergistic effect from coordination modes of Hqlc ligand and anion effect. Complexes 5–9 are isostructural with complex 4. Eu-complexes 1–4 could provide intense and bright characteristic 5D0 → 7FJ red luminescence under UV excitation in the solid state at 298 K and 77 K. In complexes 2 and 3, the coordinate phen ligand could play the antenna role in the energy transfer process. Therefore, the luminescence lifetimes of complexes 2 (779.62 and 792.65 μs) and 3 (947.21 and 1095.59 μs) are longer than those of complexes 1 (456.93 and 499.33 μs) and 4 (283.70 and 46 469 μs) in the solid state at 298 K and 77 K. Complexes 5, 7 and 8 exhibit characteristic Sm3+, Tb3+ and Dy3+ ion luminescence. Furthermore, through controlling the concentration of complexes 3 and 4 in poly(methyl methacrylate) (PMMA), a series of 3–PMMA and 4–PMMA hybrid materials are obtained, respectively. They all display strong and characteristic red luminescence emissions at a concentration of 8%. Compared with 3 and 4, the luminescence intensities and luminescence lifetimes of 3–PMMA and 4–PMMA are increased, due to the replacement of water molecules by PMMA.

Novel Hydrogen-Bonding Cross-Linking Aggregation-Induced Emission: Water as a Fluorescent “Ribbon” Detected in a Wide Range

The development of efficient sensors for detection of the water content in a wide detection range is highly desirable for balance in many industrial processes and products. Presented herein are six novel different substituted Schiff base Zn(II) complexes, which exhibit the remarkable capability to detect traces of water in a wide linear range (most can reach 0-94%, v/v), low detection limit of 0.2% (v/v), and rapid response time of 8 s in various organic solvents by virtue of an unusual water-activated hydrogen-bonding cross-linking AIE (WHCAIE) mechanism. As a proof-of-concept, the WHCAIE mechanism is explained well by single X-ray diffraction, absorption spectra, fluorescence spectra, dynamic light scattering, 1H NMR spectra, and theoretical calculations. In addition, the molecules demonstrated their application for the detection of humidity (42-80%). These Schiff base Zn(II) complexes become one of the most powerful water sensors known due to their extraordinary sensitivity, fast response, and wide detection range for water.

Effect of different donor groups in bis(6-methoxylpyridin-2-yl) substituted co-sensitizer on the performance of N719 sensitized solar cells

Three bis(6-methoxylpyridin-2-yl) substituted pyridine-anchor co-sensitizers with different donor groups are synthesized by 1,2-diaminobenzene (named L4), 1,2-diaminocyclohexane (named L5) and 1,4-butanediamine (named L6) with the aim to obtain rigid, semi-rigid and flexible co-sensitizer molecules, respectively. Their adaptability in N719 sensitized solar cells as co-sensitizers and the effects of their molecular rigidity, conjugation and co-planarity on the performance of DSSCs are studied. The results show that these three co-sensitizers are suitable to use in N719 sensitized solar cells. However, due to the different donor groups in the molecular structure, the co-sensitization performance of the rigid co-sensitizer with a large conjugate system is better than that of semi-rigid and flexible co-sensitizers. A short circuit current density of 13.27 mA cm−2, an open circuit voltage of 0.73 V and a fill factor of 0.63 corresponding to an overall conversion efficiency of 6.16% under AM 1.5G solar irradiation were achieved when rigid L4 was used as the co-sensitizer, which is 30% higher than that for DSSCs only sensitized by N719 (5.37%) under the same conditions. Mechanistic investigations are carried out by various spectral and electrochemical characterizations.

(E)-4-Methyl-N-((quinolin-2-yl)ethylidene)aniline as ligand for IIB supramolecular complexes: synthesis, structure, aggregation-induced emission enhancement and application in PMMA-doped hybrid material

Judicious structural design employing 2-quinolinecarboxaldehyde and 4-methylaniline was used to generate the Schiff base ligand (E)-4-methyl-N-((quinolin-2-yl)ethylidene)aniline (L). Five IIB complexes, namely, [ZnLCl2] (1), [ZnL(NO3)2] (2), [ZnL(OAc)2]3 (3), [CdL(OAc)2]3 (4), and [HgLCl2] (5) have been synthesized based on L. Single-crystal X-ray diffraction analysis indicates that complexes 1, 3 and 4 exhibit 3D networks, whereas 2 and 5 form 2D layers and 1D chains, respectively. TD-DFT calculations show a good correlation with the UV-vis absorption assigned to π → π* intraligand transitions. Furthermore, complexes 1-5 displayed strong greenish luminescent emissions (518-524 nm) in the aggregate state but weak emissions in solution (aggregation-induced emission enhancement), which may be due to the existence of C-HCl/O hydrogen bonding and ππ stacking interactions, resulting in restriction of intramolecular rotation (RIR). Variable-concentration 1H NMR studies suggested that the aggregates undergo intramolecular changes in conformation due to intermolecular interactions. Moreover, the emission intensity and lifetime exhibited obvious increases induced by mechanical grinding and temperature reduction, which were also attributed to AIEE properties. Subsequently, complex 1 was incorporated into poly(methyl methacrylate) (PMMA), whereby 1-PMMA exhibited enhanced emission intensity (20-fold increase in comparison with that of 1), which offers opportunities for use in plastic greenhouses to increase leaf photosynthesis.

Self-assembly of two supramolecular indium(III) metal–organic frameworks for reversible iodine capture and large band gap change semiconductor behavior

Under self-assembly, a novel polydentate benzimidazole ligand 2-(quinoline-2-yl)-benzimidazole (2-QLBM) and two In(III) compounds, [In(2-Hqlca)2Cl3·3H2O] (1) and {[In(2-QLBM)(2-qlca)Cl2]2·CH3CN·2H2O} (2) (2-Hqlca = 2-quinolinecarboxylic acid) have been synthesized and characterized. Both the In(III) compounds are driven by noncovalent interactions to assemble into supramolecular metal–organic frameworks (MOFs). Considering 2-QLBM and 2-Hqlc ligands with different geometrical structures, compound 1 possesses a (66)-dia network with a channel diameter of about 1.856 A, and compound 2 displays a (3,4)-connected topology network with the Schlafli symbol of (63)(65·8), whose channel diameter is about 3.683 A. Owing to large voids in the framework, 2 can serve as a host for reversible encapsulation of iodine corresponding to the 1.52 molecules of iodine per formula unit with a fast response and high sensitivity. Upon irradiation with UV light, the two compounds display tunable fluorescence emission from blue to yellow by varying the temperature. Moreover, the absorption spectra demonstrate that the band gaps of compounds 1 and 2 are 3.71 and 3.58 eV, respectively. When adsorbing iodine into the framework, the host structure of 2 is relatively perturbed by the presence of guests and exerts a remarkable influence on the band size and gap state.

Influence of anchoring group numbers in an efficient pyridine-anchor co-adsorbent of pyridinecarboxaldimine substituted aminonaphthalene on the performance of N719 sensitized solar cells

Unsymmetrical (N-(2-pyridinecarboxaldimine)-1-aminonaphthalene, USP) and symmetrical (N,N′-bis-(2-pyridinecarboxaldimine)-1,8-diaminonaphthalene, SDP) pyridine-anchor co-adsorbents with different numbers of anchoring groups are synthesized and employed in combination with a ruthenium complex N719 in dye sensitized solar cells (DSSCs). Both the prepared co-adsorbents can overcome the deficiency of N719 absorption in the low wavelength region of the visible spectrum, offset competitive visible light absorption of I3−, suppress the charge recombination and prolong the electron lifetime. The SDP co-adsorbent containing double anchoring groups shows better electronic coupling with TiO2 than the USP co-adsorbent with a single anchoring group. This enhanced electronic coupling leads SDP to exhibit better performance for DSSCs. A short circuit current density of 13.19 mA cm−2, an open circuit voltage of 0.75 V and a fill factor of 0.66 corresponding to an overall conversion efficiency of 6.51% under AM 1.5G solar irradiation are achieved when SDP is used as a co-adsorbent, which is much higher than that for DSSCs only sensitized by N719 (5.28%) under the same conditions.

Effect of noncovalent interactions on Ag(I)/Cu(II) supramolecular architecture for dual-functional luminescence and semiconductive properties

Four novel luminescent materials, namely, [Ag3(3,2′,3′-dpob)(bpy)]n (1·Ag), [Ag(3,3′,4′-H2dpob)(bpy)]n (2·Ag), [Ag3(3,2′,3′-Hdpob)(3,2′,3′-H2dpob)(bib)3·2H2O]n (3·Ag), and [Cu(3,2′,3′-Hdpob)(bib)·2H2O]n (4·Cu) [3,2′,3′-H3dpob = 3-(2′,3′-dicarboxylphenoxy)benzonic acid; 3,3′,4′-H3dpob = 3-(3′,4′-dicarboxylphenoxy)benzonic acid; bpy = 4,4′-bipyridine; bib = 1,4-bis(1-imidazoly)benzene] have been hydrothermally synthesized by mixed ligands and characterized using single crystal X-ray diffraction, infrared (IR), elemental analysis and thermogravimetric analysis (TGA). The crystal structures of four compounds indicate that the hydrogen bonding (O–H⋯O, C–H⋯O and C–H⋯π) and π⋯π stacking interactions play critical roles in the formation of the extended supramolecular array. 1·Ag displays a rare 3D compact structure with a 1D right-handed helical chain [–Ag1–CO2–Ag3–CO2–Ag1–]. 2·Ag and 3·Ag exhibit a 3D supramolecular architecture linked by intermolecular hydrogen bonds based on a 1D double-chain and 1D triple-chain, respectively. 4·Cu shows a 1D + 1D → 2D sheet, which is propagated to form an extended 3D structure with pcu (primitive cubic) topology via π⋯π stacking. The four compounds display remarkable narrow band emission with smaller full width at half-maximum (FWHM) (77 K, 97.91, 92.27, 72.98 and 77.96 nm; 298 K, 169.41, 241.98, 293.66 and 148.50 nm) in the solid state. The combination of such narrow FWHM and the red-shift from 298 K to 77 K endow them with a prominent thermochromic effect. It is worth noting that 2·Ag and 3·Ag display good aggregation-induced emission (AIE) properties. Both of them show very weak luminescence in dimethyl sulfoxide (DMSO, good solvent) while their intensities increased enormously with the addition of water (H2O, poor solvent) due to aggregation. In addition, adsorption spectra reveal their semiconductive nature (2.35 eV for 1·Ag and 2.91 eV for 3·Ag) and the role of Ag⋯Ag interactions in controlling the performance of semiconductive properties is highlighted.

Variable temperature spectroelectrochemistry study of silver-doped TiO2 and its influence on the performance of dye sensitized solar cells

Ag-doped TiO2 nanoparticles are prepared and used as semiconductor materials of photoanodes to improve the performance of dye sensitized solar cells (DSSCs). The results of variable temperature spectroelectrochemistry study show that the conduction band edge of Ag-doped TiO2 shifts positively, which enhances the driving force of electrons and improves the electron injection efficiency from the LUMO of the dye to the conduction band of TiO2. The deposition of Ag not only benefits efficient charge transfer but also could minimize the charge recombination process, resulting in a significant photocurrent enhancement. At the optimum Ag concentration of 1.2 at%, the DSSC exhibited a Jsc of 19.75 mA cm−2, a Voc of 0.73 V, and a FF of 0.57 with an energy conversion efficiency (η) of 7.34%, indicating a 57% and 30% increase in Jsc and η respectively than that of DSSC based on an undoped TiO2 photoanode, which gives a Jsc of 12.61 mA cm−2, a Voc of 0.75 V, and a FF of 0.59 with a η of 5.64%.