Yaokang Lv

Dipole‐Induced Band‐Gap Reduction in an Inorganic Cage

Metal-doped polyoxotitanium cages are a developing class of inorganic compounds which can be regarded as nano- and sub-nano sized molecular relatives of metal-doped titania nanoparticles. These species can serve as models for the ways in which dopant metal ions can be incorporated into metal-doped titania (TiO2 ), a technologically important class of photocatalytic materials with broad applications in devices and pollution control. In this study a series of cobalt(II)-containing cages in the size range ca. 0.7-1.3 nm have been synthesized and structurally characterized, allowing a coherent study of the factors affecting the band gaps in well-defined metal-doped model systems. Band structure calculations are consistent with experimental UV/Vis measurements of the Tix Oy absorption edges in these species and reveal that molecular dipole moment can have a profound effect on the band gap. The observation of a dipole-induced band-gap decrease mechanism provides a potentially general design strategy for the formation of low band-gap inorganic cages.

Polymorphic crystals and their luminescence switching of triphenylacrylonitrile derivatives upon solvent vapour, mechanical, and thermal stimuli

For piezo-, vapo-, and thermochromic materials, it remains a challenge to figure out the underlying reason for fluorescence color changes upon external stimulation and determine why only some fluorophores reveal emission switching. A novel triphenylacrylonitrile derivative (TPAN-MeO) with remarkably twisted conformations has been carefully prepared via the Suzuki coupling reaction. The fluorescence of TPAN-MeO in the aggregate state depends on the polymorphic forms: three crystalline forms BCrys, SCrys and YCrys exhibit bright blue, sky-blue and yellow emission, respectively; meanwhile the amorphous powders are also strongly fluorescent with green emission. The crystals BCrys and SCrys exhibit mechano- and piezochromism in that grinding and high pressure could alter the emission colour, respectively. In addition, the amorphous film exhibits vapo- and thermochromic behaviour in that organic vapour and heating could change the green colour into sky-blue. Interestingly, the solvent vapour and heating stimuli can trigger a crystal-to-crystal transformation between SCrys form and YCrys form.

Formation of Ti28Ln Cages, the Highest Nuclearity Polyoxotitanates (Ln=La, Ce)

The solvothermal reactions of Ti(OEt)(4) with LnCl(3) (Ln = La, Ce) produced new Ti(28) Ln cages, in which the Ln(3+) ions are coordinated within a metallocrown arrangement, which represents the highest nuclearity cages of this type (see figure).

Encapsulation of a ‘naked’ Br− anion in a polyoxotitanate host

Solvothermal reaction of Ti(OiPr)4 with CoBr2 in iPrOH at 150 °C gives the ion-separated compound [Ti12O15(OiPr)17]+[(BrCo)6Ti15O24(OiPr)18(Br)]−, the heterometallic Ti15Co6 anion of which contains a Br− ion trapped within a polyoxotitanate shell. This arrangement provides evidence of new host–guest chemistry in this area.

A study of the optical properties of metal-doped polyoxotitanium cages and the relationship to metal-doped titania

To what extent the presence of transition metal ions can affect the optical properties of structurally well-defined, metal-doped polyoxotitanium (POT) cages is a key question in respect to how closely these species model technologically important metal-doped TiO2. This also has direct implications to the potential applications of these organically-soluble inorganic cages as photocatalytic redox systems in chemical transformations. Measurement of the band gaps of the series of closely related polyoxotitanium cages [MnTi14(OEt)28O14(OH)2] (1), [FeTi14(OEt)28O14(OH)2] (2) and [GaTi14(OEt)28O15(OH)] (3), containing interstitial Mn(II), Fe(II) and Ga(III) dopant ions, shows that transition metal doping alone does not lower the band gaps below that of TiO2 or the corresponding metal-doped TiO2. Instead, the band gaps of these cages are within the range of values found previously for transition metal-doped TiO2 nanoparticles. The low band gaps previously reported for 1 and for a recently reported related Mn-doped POT cage appear to be the result of low band gap impurities (most likely amorphous Mn-doped TiO2).

A low-temperature single-source route to an efficient broad-band cerium(III) photocatalyst using a bimetallic polyoxotitanium cage

Aqueous hydrolysis of a series of cerium-containing polyoxotitanium cages gives Ce(III)-doped TiO2 [TiO2(Ce)] or TiO2-supported Ce(III)2Ti2O7, depending on the starting Ti:Ce ratio of the precursor. TiO2-supported Ce2Ti2O7 exhibits superior photocatalytic activity to the Ce-doped TiO2 materials and unusual broad-band absorption behaviour across the visible and near-infrared regions.

An integrated electrochromic supercapacitor based on nanostructured Er-containing titania using an Er(III)-doped polyoxotitanate cage

The novel heterometallic polyoxotitanate cage [Ti8O7(OEt)21Er] can be used as a single-source precursor for the formation of nanostructured Er-containing titania materials (Er@TiO2). Based on the electrochromic properties and lithium ion storage capacity of Er@TiO2, an integrated bifunctional EC supercapacitor has been designed.

Novel Eu-containing titania composites derived from a new Eu(III)-doped polyoxotitanate cage

A new Eu(III)-doped polyoxotitanate (POT) cage [Ti2O(OEt)8(EtOH)EuCl]2 can be used as a single-source precursor for the formation of nanostructured Eu-containing titania composites and flexible fluorescent films, which exhibit significant red luminescence and are attractive fluorescent materials.

A novel ferrocene-containing aniline copolymer: its synthesis and electrochemical performance

A novel ferrocene-containing aniline, 6-(2-amino-phenol-9H-yl)-hexyl ferrocenecarboxylate (AnFc) was synthesized via the hydrogenation of 6-(2-nitro-phenol-9H-yl)-hexyl ferrocenecarboxylate (NPFc). Then, the homopolymer of AnFc (PAnFc), copolymers of aniline and AnFc (P(An-co-AnFc)), and polyaniline (PAn) were prepared using a chemical oxidative polymerization process. The structure, morphology, and electrochemical properties of the prepared polymers were characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet visible spectroscopy (UV-vis), scanning electron microscopy (SEM), cyclic voltammograms (CV) and galvanostatic charge–discharge tests. The results demonstrated that the AnFc functionalized monomer and the corresponding polymer derivatives have been synthesized successfully, and the introduction of the novel functionalized ferrocene-based aniline obviously affected the spectral characteristic, morphology and electrochemical characteristics of the electro-active polymers obtained, as well as its charge migration along the polymer backbone. In addition, the charge–discharge tests showed that P(An-co-AnFc) improved the discharge plateau in the potential range of about 3.0–4.0 V and with an acceptable initial discharge specific capacity of 104.9 mA h g−1 for P(An-co-AnFc) (5 : 1 ([An]/[AnFc])) (compared with 108.2 mA h g−1 for PAn). Furthermore, P(An-co-AnFc) exhibited an even more improved cycling stability than that of PAn, and after 30 cycles the discharge capacity of P(An-co-AnFc) (3 : 1 ([An]/[AnFc])) still maintained 76.3% of the capacity obtained during the initial cycle.

Enhanced electrochromic switching speed and electrochemical stability of conducting polymer film on an ionic liquid functionalized ITO electrode

The 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) functionalized ITO substrate was successfully prepared via a solution immersion method and then incorporated with poly(4,4′,4′′-tris[4-(2-bithienyl)phenyl]amine) (PTBTPA) to form the PTBTPA–[BMIM]BF4 film by electrochemical polymerization, which presents reversible multicolor changes from orange, olive green to dark gray. Interestingly, compared with the bleaching time (tb) and the coloring time (tc) of the pure PTBTPA film (1.76 s and 4.51 s) at 1100 nm, the PTBTPA–[BMIM]BF4 film exhibits shorter tb and tc (0.87 s and 2.90 s) at the same wavelength. Obviously, the switching speed of the PTBTPA–[BMIM]BF4 film has been improved significantly, and it is further supported by the electrochemical impedance spectra which demonstrate that the PTBTPA–[BMIM]BF4 film possesses much lower charge transfer resistance. The reduction of charge transfer resistance could be attributed to (1) the private channel provided by the ionic liquid [BMIM]BF4 as a linker between the polymer and the electrode; (2) the ability of the simultaneous doping and dedoping of ClO4− in the electrolyte and BF4− ions of the ionic liquid. Moreover, the cyclic stability studies reveal that the PTBTPA–[BMIM]BF4 film exhibits better durability and retains 70.4% of its original electroactivity after 500 cycles in ionic liquid solution. The results demonstrate that the electrochemical and the electrochromic performances could be significantly enhanced through incorporating PTBTPA with the ionic liquid ([BMIM]BF4).