Phase behaviour of the thermotropic cubic mesogen 1,2-bis-(4- n -octyloxybenzoyl)hydrazine under pressure

The phase transition behaviour of an optically isotropic, thermotropic cubic mesogen 1,2-bis-(4-n-octyloxybenzoyl)hydrazine, BABH(8), was investigated under pressures up to 200 MPa using a high pressure differential thermal analyser, wide-angle X-ray diffraction and a polarizing optical microscope equipped with a high pressure optical cell. The phase transition sequence, low temperature crystal (Cr₂)-high temperature crystal (Cr ₁)- cubic (Cub)-smectic C (SmC)-isotropic liquid (I) observed at atmospheric pressure, is seen in the low pressure region below about 30 MPa. The cubic phase disappears at high pressures above 30–40 MPa, in conjunction with the disappearance of the Cr₁ phase. The transition sequence changes to Cr₂-SmC-I in the high pressure region. Since only the Cub-SmC transition line among all the phase boundaries has a negative slope (dT/dP) in the temperature-pressure phase diagram, the temperature range for the cubic phase decreases rapidly with increasing pressure. As a result, a triple point was estimated approximately as 31.6 ±2.0 MPa, 147.0±1.0°C for the SmC, Cub and Cr₁ phases, indicating the upper limit of pressure for the observation of the cubic phase. Reversible changes in structure and optical texture between the Cub and SmC phases were observed from a spot-like X-ray pattern and dark field for the cubic phase to the Debye-Sherrer pattern and sand-like texture for the SmC phase both in isobaric and isothermal experiments.     

Ion‐Pair‐Based Assemblies Comprising Pyrrole–Pyrazole Hybrids

Modified 3,5‐dipyrrolylpyrazole (DPP) derivatives in their protonated form produce planar [2+2]‐type complexes with trifluoroacetate (TFA) ions. These complexes serve as constituent components of ion‐pair‐based assemblies. An essential strategy for the construction of dimension‐controlled organized structures based on these [2+2]‐type complexes is the introduction of aryl rings bearing long alkyl chains, which enables the formation of 2D patterns at interfaces, supramolecular gels, and mesophases.     

Formation and Geometrical Control of Polygon‐Like Metal‐Coordination Assemblies

Polygon‐like [2+2]‐ and [3+3]‐type metal complexes were prepared from dipyrrin dimers connected by acute‐angled spacers. The electrical conduction depends strongly on the packing alignment of the compounds, revealing the presence of effective hopping pathways for holes with relatively high mobility up to 0.11 cm² V^?1 s^?1 along the aligned axis of [3+3]‐type metal‐bridged assemblies. These observations correlated with the geometrical control of the π‐conjugated metal complexes in the cyclic structures, which enables their ordered arrangement in the assemblies.     

Corannulene‐Fused Anion‐Responsive π‐Conjugated Molecules that Form Self‐Assemblies with Unique Electronic Properties

The fusion of bowl‐shaped π‐conjugated corannulene units to anion‐responsive π‐conjugated dipyrrolyldiketone‐boron complexes resulted in new molecular materials with a unique self‐assembly capability. The bowl‐fused receptor with aliphatic tails could form both supramolecular gels and mesophases through π‐stacking interactions and also exhibited anion‐responsive characteristics. The presence of the π‐bowl unit not only afforded enhanced self‐assembly capability both in solution and in the mesophases, as evidenced by gelation experiments and phase‐transition profiles, but also enhanced intrinsic charge‐carrier mobility.     

Emission and transient absorption measurements of substitution effects of C–C triple bonds on relaxation processes of the fluorescent state of naphthalenes

Photophysical and photochemical properties of naphthalenes substituted with trimethylsilylethynyl, tert-butylethynyl, and trimethylsilylbutadiynyl groups were investigated by measurement of fluorescence yields, lifetimes, and triplet absorption. Introducing trimethylsilylethynyl and tert-butylethynyl groups to the 1-position of the naphthalene skeleton substantially enhanced fluorescence and intersystem crossing (ISC). The rates of fluorescence of 2-substituted naphthalenes were low. The effect of ethynyl groups on the 1-substituted naphthalenes was rationalized in terms of an increase of the transition moment along the short axis of the naphthalene skeleton. Substitution of the trimethylsilylbutadiynyl group at the 1 or 2-position of the naphthalene skeleton caused a considerable decrease in the fluorescence yield (approximately 0.01) and an increase in the ISC yield (0.99).     

Visible‐Light‐Driven CO2 Reduction with Carbon Nitride: Enhancing the Activity of Ruthenium Catalysts

A heterogeneous photocatalyst system that consists of a ruthenium complex and carbon nitride (C₃N₄), which act as the catalytic and light‐harvesting units, respectively, was developed for the reduction of CO₂ into formic acid. Promoting the injection of electrons from C₃N₄ into the ruthenium unit as well as strengthening the electronic interactions between the two units enhanced its activity. The use of a suitable solvent further improved the performance, resulting in a turnover number of greater than 1000 and an apparent quantum yield of 5.7 % at 400 nm. These are the best values that have been reported for heterogeneous photocatalysts for CO₂ reduction under visible‐light irradiation to date.     

Oscillatory Reaction of a Pendant Drop in a Liquid–Air System under Microwave Irradiation

A Belousov–Zhabotinsky reaction in a pendant drop under microwave radiation was observed under nonstirring conditions. The period decreased as the irradiation power and time were increased because the droplet temperature increased. Moreover, the color change of the solution during the oscillatory reaction depended on the irradiation power and time although the droplet temperature returned to room temperature quickly. Irradiation at higher powers or longer times suspended the oscillatory reaction. However, for moderate irradiation powers or times, the oscillatory reaction stopped after irradiation because the concentration distribution of the reagents became homogeneous. After a time, the oscillatory reaction restarted because a concentration gradient developed again. Accordingly, the effect of the microwave irradiation history continued because the oscillatory reaction stopped even after the irradiation was stopped. This is because the rotation of the polar molecule caused by the irradiation produced a flat concentration distribution for the reagents through increased molecular diffusion.     

Influence of 4‐fluorophenyl pendants in thieno[3,4‐b]thiophene‐benzo[1,2‐b:4,5‐b′]dithiophene‐based polymers on the performance of photovoltaics

Polymers consisting of benzo[1,2‐b:4,5‐b′]dithiophene and thieno[3,4‐b]thiophene units (PTB‐based polymers), either fully or partially containing 4‐fluorophenyl pendants, are synthesized as electron donor materials for inverted‐type polymer solar cells (PSCs). The influence of the 4‐fluorophenyl pendant content on the thermal and optical properties, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), the hole mobilities, and photovoltaic performances are investigated. As the 4‐fluorophenyl pendant content increased, the HOMO and LUMO of the polymers were deepened proportionally and the open‐circuit voltages of the PSCs improved. Incorporation of 4‐fluorophenyl pendants into the polymers also affected the crystallinity, orientation, and compatibility with [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester in the active layers, leading to nonlinearities in the short‐circuit current densities, and fill factors. The incorporation of an appropriate number of 4‐fluorophenyl pendants enhanced the power conversion efficiencies of the PSC devices from 2.25 to 3.96% for identical device configurations. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1586–1593