Y.F.Wang

Analytically pure C₆₀H₁₈ is obtained by a Ru₃ cluster complexation and decomplexation method. The crystal structure of C₆₀H₁₈ consists of one flattened hemisphere, to which all 18 hydrogen atoms are symmetrically bonded, and one curved hemisphere akin to C₆₀. A benzenoid ring in the flattened hemisphere is isolated from the residual π systems by a belt composed of sp³-hybridized CH units. The average out-of-plane distances for carbon atoms attached to the benzenoid ring (0.14 Å) is substantially larger than that found in C₆₀F₁₈ (0.06 Å). Several long C(sp³)C(sp³) single bond lengths [1.61(3)–1.65(3) Å] are observed for C₆₀H₁₈. The reaction of [Ru₃(CO)₁₂] and C₆₀H₁₈ produces [Ru₃(CO)₉(μ₃-η²,η²,η²-C₆₀H₁₈)] (1), where the Ru₃ triangle is regiospecifically linked to the hexagon opposite to the benzenoid ring. Compound 1 is the first transition metal complex of a polyhydrofullerene (fullerane). C₆₀H₁₈ and 1 have been characterized by ¹H and ¹³C NMR, UV/Vis, and mass spectroscopies. The HOMO–LUMO gap of C₆₀H₁₈ is evaluated to be 1.51 V by cyclic voltammetry.

Crowning glory: The benzenoid ring in the flattened hemisphere of C₆₀H₁₈ appears less aromatic than that in C₆₀F₁₈. Several long C(sp³)C(sp³) bond lengths [1.61(3)–1.65(3) Å] are observed. The reaction of C₆₀H₁₈ with [Ru₃(CO)₁₂] produces [Ru₃(CO)₉(μ₃-η²,η²,η²-C₆₀H₁₈)], which is the first transition metal complex of a polyhydrofullerene (fullerane).

Bis-silylated and bis-germylated derivatives of Lu₃N@I_h-C₈₀ (3, 4, 5) were successfully synthesized by the photochemical addition of disiliranes 1 a, 1 b or digermirane 2, and fully characterized by spectroscopic, electrochemical, and theoretical studies. Interestingly, digermirane 2 reacts more efficiently than disiliranes 1 a and 1 b because of its good electron-donor properties and lower steric hindrance around the GeGe bond. The 1,4-adduct structures of 3, 4, 5 were unequivocally established by single-crystal X-ray crystallographic analyses. The electrochemical and theoretical studies reveal that the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the 1,4-adducts are remarkably smaller than those of Lu₃N@I_h-C₈₀, because the electron-donating groups effectively raise the HOMO levels. It is also observed that germyl groups are slightly more electron-donating than the silyl groups on the basis of the redox properties and the HOMO–LUMO energies of 4 and 5. Bis-silylation and bis-germylation are effective and versatile methods for tuning the electronic characteristics of endohedral metallofullerenes.

Electronic tuning of fullerenes: Bis-silylated and bis-germylated Lu₃N@I_h-C₈₀ derivatives have been synthesized using photochemical additions of disilirane and digermirane. The electrochemical and theoretical studies of these adducts demonstrate that bis-silylation and bis-germylation are effective methods for tuning the electronic characteristics of Lu₃N@I_h-C₈₀.

Conjugated microporous polymers are a unique class of polymers that combine extended π-conjugation with inherent porosity. However, these polymers are synthesized through solution-phase reactions to yield insoluble and unprocessable solids, which preclude not only the evaluation of their conducting properties but also the fabrication of thin films for device implementation. Here, we report a strategy for the synthesis of thin films of π-conjugated microporous polymers by designing thiophene-based electropolymerization at the solution–electrode interface. High-quality films are prepared on a large area of various electrodes, the film thickness is controllable, and the films are used for device fabrication. These films are outstanding hole conductors and, upon incorporation of fullerenes into the pores, function as highly efficient photoactive layers for energy conversions. Our film strategy may boost the applications in photocatalysis, energy storage, and optoelectronics.

Film formation: A general strategy for synthesizing thin films of π-conjugated microporous polymers is described (see picture). Using a thiophene-based high-throughput electropolymerization it was possible to control the thickness of the films. The π-conjugated microporous polymers are shown to be outstanding conductors with a high carrier mobility and photoactive layers for efficient conversion of photoenergy.

Novel steric bulky hole transporting materials (HTMs) with two or four N,N-di(4-methoxyphenyl)aminophenyl units have been synthesized. When the EtheneTTPA was used as a hole transporting material in perovskite solar cell, the power conversion efficiency afforded 12.77 % under AM 1.5 G illumination, which is comparable to the widely used spiro-OMeTAD based solar cell (13.28 %).

On the hole: The development and properties of novel hole transporting materials (HTMs) for perovskite solar cells is presented. The synthesis of two HTMs (see figure) by incorporating an ethylene unit into the triphenylamine unit is described.

Invited for the cover of this issue are the groups of M. Kako (The University of Electro-Communications, Japan), M. M. Olmstead (University of California, USA), A. L. Balch (University of California, USA), S. Nagase (Kyoto University, Japan), T. Akasaka (University of Tsukuba, Japan). The image depicts the 1,4-bis-silylated and 1,4-bis-germylated structures of Lu₃N@I_h-C₈₀, which represent rare examples of the crystallographic studies of functionalized Lu₃N@I_h-C₈₀. Read the full text of the article at 10.1002/chem.201502511.

“The interplay between experiment and theory certainly played an important role in accomplishing our work” Read more about the story behind the cover in the Cover Profile and about the research itself on page 16411 ff. (DOI: 10.1002/chem.201502511).

The use of methane as a reactive gas dramatically increases the selectivity of the arc-discharge synthesis of M-Ti-carbide clusterfullerenes (M=Y, Nd, Gd, Dy, Er, Lu). Optimization of the process parameters allows the synthesis of Dy₂TiC@C₈₀-I and its facile isolation in a single chromatographic step. A new type of cluster with an endohedral acetylide unit, M₂TiC₂@C₈₀, is discovered along with the second isomer of M₂TiC@C₈₀. Dy₂TiC@C₈₀-(I,II) and Dy₂TiC₂@C₈₀-I are shown to be single-molecule magnets (SMM), but the presence of the second carbon atom in the cluster Dy₂TiC₂@C₈₀ leads to substantially poorer SMM properties.

Carbide inclusion: The use of methane as a reactive gas dramatically increases the selectivity of the arc-discharge synthesis of M₂TiC@C₈₀ carbide clusterfullerenes (M=lanthanide). The new single-molecule magnet Dy₂TiC@C₈₀ could be readily isolated.

Seven SGT organics dyes, containing bis-dimethylfluoreneyl amino groups with a dialkoxyphenyl unit as an electron donor and a cyanoacrylic acid group as an anchoring group, connected with oligothiophenes, fused thiophenes and benzothiadiazoles as π-bridges, were designed and synthesised for applications in dye-sensitised solar cells (DSSCs). The photovoltaic performance of DSSCs based on organic dyes with oligothiophenes depends on the molecular structure of the dyes, in terms of the length change of the π-bridging units. The best performance was found with a π-bridge length of about 6 Å. To further enhance the photovoltaic performance associated with this concept, cyclopenta[1,2-b:5,4-b′]dithiophene (CPDT) and benzothiadiazole were introduced into the π-bridge unit. As a result, the DSSC based on the organic dye containing the CPDT moiety showed the best photovoltaic performance with a short-circuit photocurrent density (J_sc) of 14.1 mA cm⁻², an open-circuit voltage (V_oc) of 0.84 V and a fill factor (FF) of 0.72, corresponding to an overall conversion efficiency (η) of 8.61 % under standard AM 1.5 irradiation.

How long is the ideal bridge? The photovoltaic performance of DSSCs based on organic dyes with oligothiophenes depends on the molecular structure of the dyes in terms of the length of the π-bridge. The organic dyes, consist of bisdimethylfluoreneyl amino groups with a dialkoxyphenyl unit as the electron donor and a cyanoacrylic acid group as an anchoring group, and are connected to oligothiophenes, fused thiophenes and electron-withdrawing benzothiadiazoles as π-bridging units (an example is shown here).

A novel hole-transporting molecule (F101) based on a furan core has been synthesized by means of a short, high-yielding route. When used as the hole-transporting material (HTM) in mesoporous methylammonium lead halide perovskite solar cells (PSCs) it produced better device performance than the current state-of-the-art HTM 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD). The F101-HTM-based device exhibited both slightly higher J_sc (19.63 vs. 18.41 mA cm⁻²) and V_oc (1.1 vs. 1.05 V) resulting in a marginally higher power conversion efficiency (PCE) (13.1 vs. 13 %). The steady-state and time-resolved photoluminescence show that F101 has significant charge extraction ability. The simple molecular structure, short synthesis route with high yield and better performance in devices makes F101 an excellent candidate for replacing the expensive spiro-OMeTAD as HTM in PSCs.

Hole in one? An electron-rich molecule containing furan as core and arylamine as side groups has been synthesized. When employed as a hole-transporting material (HTM) in a CH₃NH₃PbI₃ perovskite solar cell, power conversion efficiencies of over 13 % are obtained. This HTM, owing to its simple synthesis and high performance, has great potential to replace the more expensive 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene as the HTM in perovskite solar cells.

It is generally believed that silver or silver-based compounds are not suitable counter electrode (CE) materials for dye-sensitized solar cells (DSSCs) due to the corrosion of the I⁻/I₃⁻ redox couple in electrolytes. However, Ag₂S has potential applications in DSSCs for catalyzing I₃⁻ reduction reactions because of its high carrier concentration and tiny solubility product constant. In the present work, CE manufactured from Ag₂S nanocrystals ink exhibited efficient electrocatalytic activity in the reduction of I₃⁻ to I⁻ in DSSCs. The DSSC consisting of Ag₂S CE displayed a higher power conversion efficiency of 8.40 % than that of Pt CE (8.11 %). Moreover, the devices also showed the characteristics of fast activity onset, high multiple start/stop capability and good irradiated stability. The simple composition, easy preparation, stable chemical property, and good catalytic performance make the developed Ag₂S CE as a promising alternative to Pt CE in DSSCs.

Energy conversion: A counter electrode manufactured from Ag₂S nanocrystal ink exhibited efficient electrocatalytic activity in the reduction of I₃⁻ to I⁻ in dye-sensitized solar cells (see figure; DSSCs, η=8.40 %).The simple composition, easy preparation, stable chemical properties and good catalytic performance make the newly developed Ag₂S a promising alternative to Pt in DSSCs.

A new p–n heterojunction photocatalyst has been synthesized successfully through chemical-bond-mediated combination of coordination polymer nanoplates (CPNPs) and partially reduced graphene oxide (PRGO) with a simple colloidal blending process. Photocatalytic H₂ production by the p–n heterojunction photocatalyst PRGO/CPNP was investigated under visible-light irradiation, which illustrates that PRGO/CPNP exhibits a much higher photocatalytic H₂ production rate than neat the CPNPs. The improvement of this photocatalytic property can be attributed to the inner electrical field formed in the p–n heterojunction, which impedes recombination of photogenerated electrons and holes. In PRGO/CPNP, the existence of the p–n heterojunction has been confirmed by electrochemical methods clearly. For PRGO/CPNP, the reductive degree of the PRGO has a great influence on the H₂ production rate and an ideal condition to get a PRGO/CPNP photocatalyst with higher performance has been obtained.

Taking the right way: A p–n heterojunction photocatalyst based on coordination polymer nanoplates (CPNPs) and partially reduced graphene oxide (PRGO) has been fabricated successfully, which displays an excellent H₂ production rate under visible-light irradiation (see figure; CB=conductive band, VB=valence band). Furthermore, the influence of the partially reduced graphene oxide on the H₂ production rate is also discussed.