On the basis of fundamental research on the chemistry of π-electron systems between heavier main group elements, it was found that such π-electron systems should exhibit higher HOMO and lower LUMO as compared with those between second row elements. That is, the π-electron systems between heavier main group elements are possibly good electron acceptors, good electron donors, and good electron transporters. From the viewpoint of creation of novel π-electron systems and fundamental research on such π-electron system of heavier main group elements, a novel type of doubly and triply bonded compounds between heavier group 14 elements was successfully synthesized by taking advantage of kinetic stabilization using bulky substituents. The new family of multiple-bond compounds obtained here are (i) 1,2-dibromodimetallenes, Ar(Br)E=E(Br)Ar (E = Si, Ge, Ar = bulky aryl group), as a possible building block of a π-bond between heavier group 14 elements, (ii) 1,2-diaryldimetallynes (ArE≡EAr, E = Si, Ge) as a unique and reactive π-bonding, and (iii) 1,2-dihydrodisilenes, Ar(H)Si=Si(H)Ar, as a simple disilene. The fundamental physical and chemical properties of the newly obtained compounds have been revealed, showing that such π-electron systems between heavier group 14 elements should be completely different from those of carbon systems and should be of great interest as unique π-systems. Thus, the compounds obtained here are not only “stable multiple bonds” but also possible candidates for novel material species.
From the viewpoint of creation of novel π-electron systems and fundamental research on such π-electron systems of heavier main group elements, a novel type of doubly and triply bonded compounds between heavier group 14 elements was successfully synthesized by taking advantage of kinetic stabilization using bulky substituents. The new family of multiple-bond compounds obtained here are (i) 1,2-dibromodimetallenes, Ar(Br)E=E(Br)Ar (E = Si, Ge, Ar = bulky aryl group), as a possible building block of a π-bond between heavier group 14 elements, (ii) 1,2-diaryldimetallynes (ArE≡EAr, E = Si, Ge) as a unique and reactive π-bonding, and (iii) 1,2-dihydrodislenes, Ar(H)Si=Si(H)Ar, as a simple disilene.
Through thermodynamic, spectroscopic, and structural studies, the molten state of the alkyl chain in SmE phase, which is the liquid-crystalline mesophase closest to an ordered crystalline phase, has been established in a calamitic mesogen nPA. Combining the same conclusion for the SmE phase of another calamitic mesogen nTCB, it is concluded that the alkyl chain attached at end(s) of a rod-like core is molten in any liquid-crystalline mesophase. The thermodynamic implications are briefly discussed.
In any liquid-crystalline mesophases of calamitic mesogens, established is the molten state of the alkyl chain attached at the end(s) of mesogenmic core, the conformational entropy of which stabilizes the mesophase.
Two cobaloxime complexes, namely (3-cyanopropyl)(3-phenylazopyridine)cobaloxime and (3-cyanopropyl)(4-phenylazopyridine)cobaloxime, were synthesized as new dual photoisomeric complexes for controlling the reactivity of trans–cis photoisomerization of phenylazopyridine derivatives in the solid state. The phenylazopyridine moieties of the crystals were transformed from the trans to the cis-form on exposure to UV light. In contrast, the 3-cyanopropyl groups of the crystals were isomerized to 1-cyanopropyl groups on irradiation with visible light. Moreover, the 3–1 photoisomerization of the 3-cyanopropyl group occurred with retention of the single-crystal form. The rates of the trans–cis transformations of the phenylazopyridine moieties of the crystals before the 3–1 phototransformation were compared with those after the phototransformation in the solid state. For the two crystals, the rates of the trans–cis phototransformations significantly increased after 3–1 photoisomerization. The crystal structures before and after 3–1 photoisomerization were analyzed. The free space around the phenylazopyridine moieties expanded as a result of 3–1 photoisomerization. It is clear that the reaction rates of the trans–cis transformations of the phenylazopyridine moieties on exposure to UV light can be modified by introducing another photoreactive group that is photoisomerized by visible light.
Photochemical reactions of 4-[(10-sulfanyldecyl)oxy]benzophenone with deuterated polystyrene (PS-d8) were studied using Fourier-transform infrared (FT-IR) spectroscopy and vibrational sum frequency generation (VSFG) spectroscopy. The FT-IR spectral changes of PS thin films indicated that exposure to ultraviolet (UV) light caused photochemical consumption of the benzophenone moiety by a hydrogen abstraction reaction of the carbonyl group; the reaction was almost complete at an exposure energy of 2.0 J cm−2 at 254 nm. The VSFG spectral changes of the adsorbed monolayer on Au on UV exposure revealed that the carbonyl groups oriented parallel to the Au substrate surface were consumed at more exposure energies. The exposure-energy-dependent formation of PS-grafted layers was confirmed by atomic force microscopy observations of Au surfaces modified with a photoreactive monolayer.
The antioxidant activity of ortho- and meta-substituted tryptophan derivatives has been investigated in the gas phase and water. The reaction enthalpies of antioxidant activity of studied derivatives have been calculated and compared with corresponding values of tryptophan. Results show that EWG substituents increase the BDE, IP, and ETE while EDG appendages cause a rise in the PA and PDE. The tryptophan derivatives with lowest BDE, IP, and PA values were identified as the compounds with high antioxidant activity. Results show that the substituents in ortho-position have high potential for synthesis of novel tryptophan derivatives. Results show that EDG-substituted tryptophans can process their protective role via HAT mechanism in gas phase. On the other hand, SPLET mechanism represents the thermodynamically favored process for EWG-substituted tryptophans in water. The calculated reaction enthalpies of the substituted tryptophans have linear dependences with Hammett constants and EHOMO that can be utilized in the selection of suitable substituents for the synthesis novel antioxidants based on tryptophan.
The thermal annealing effects on the photocarrier dynamics in thin films of [6,6]-phenyl C61 butyric acid methyl ester (PCBM) on quartz substrates are investigated. Both the photocarrier generation via charge-transfer state and the charge transport in PCBM films are studied by time-resolved photoconductance (PC) measurement. More than 90% of external photocarrier generation efficiency relative to the non-annealed film is reduced upon annealing of the PCBM film at high temperatures. Excitation light power dependence of PC indicates that the photocarrier in the non-annealed film is generated by a one-photon process, while photons of more than one are required in highly annealed films. The multiphotonic process for carrier generation and the substantial reduction of carrier density caused by the thermal treatment are associated with trap formation. The density of photoinjected carrier is also affected by applying external magnetic field. The observed positive magnetophotoconductance (MPC) in non-annealed film is understood in terms of the incoherent spin conversion in nongeminate electron–hole (e–h) pairs with a selective recombination from singlet e–h pairs. In highly annealed film, the broad magnetic field dependence of MPC with negative phase is suggested to originate from the detrapping of trapped carrier assisted by collision with the triplet exciton.
1-Thiazolyl-2-vinylcyclopentene derivatives, 1-(5-methoxy-2-phenyl-4-thiazolyl)-2-(2-methyl-1-phenyl-1-propenyl)perfluorocyclopentene (1a), 1-[5-methoxy-2-(4-methoxyphenyl)-4-thiazolyl]-2-(2-methyl-1-phenyl-1-propenyl)perfluorocyclopentene (2a), and 1-[5-methoxy-2-(4-methoxyphenyl)-4-thiazolyl]-2-[1-(4-methoxyphenyl)-2-methyl-1-propenyl]perfluorocyclopentene (3a) were synthesized in an attempt to obtain yellow photochromic compounds having low photocycloreversion quantum yields and large absorption coefficients of the closed-ring isomers. Their photochromic performance, thermal stability, and fatigue resistance were compared with 1-[5-methoxy-2-(4-methoxyphenyl)-4-thiazolyl]-2-(1,2-dimethyl-1-propenyl)perfluorocyclopentene (4a) having a methyl-substituted olefin. Upon irradiation with 313 nm light, compounds 1a, 2a, and 3a changed from colorless to various shades of yellow in toluene. The conversions from the open-ring (1a, 2a, and 3a) to the closed-ring (1b, 2b, and 3b) isomers in the photostationary state under irradiation with 313 nm light were 93, 95, and 98%, respectively. Among the three derivatives 3b has the largest absorption coefficient (ε = 18900 M−1 cm−1) at 428 nm and the lowest cycloreversion quantum yield of 1.8 × 10−3.
Graphene (oxide)/TiO2 composite materials have attracted widespread attention because of their scientific and technological importance as, for example, photocatalysts or electronic materials. These composites are usually prepared using high-temperature and/or slow synthetic procedures such as the hydrothermal method. Here, we demonstrate a low-temperature and relatively rapid synthesis of a graphene oxide/TiO2 composite. Graphene oxide sheets decorated with anatase TiO2 nanoparticles are successfully obtained by refluxing graphene oxide sheets dispersed in an aqueous TiOSO4 ethanol solution at 80 °C for 2 h. The graphene oxide is reduced during photocatalytic reduction of the TiO2 deposited on the surface of the graphene oxide. The reduced graphene oxide/TiO2 composite shows very high photocatalytic activity as compared with pure TiO2 and nonreduced graphene oxide/TiO2.
The solubilization of liposomes induced by the addition of surfactants was photocontrolled under temperature control. The instability of the membrane was increased both by photoisomerization of photoresponsive molecules included in the membrane and by changing temperature. By addition of a spiropyran to the liposome membrane, charge-separated structure was formed by UV irradiation, causing local polarization and subsequent motion in the membrane. We found a difference in the solubilization processes in a specific temperature range under UV irradiated and nonirradiated conditions, and figured out that the solubilization of liposomes smaller than 2 µm can be distinctly photocontrolled in a certain temperature range.
The kinetics of 3-hexylthiophene polymerization by FeCl3 was investigated. There was observed a simple and rapid rise to a maximum polymerization rate (Rp) followed by a moderate decay to a stationary Rp. The polymerization activity increased monotonically with increasing reaction temperature to correspond to an overall activation energy of 15.4 kJ mol−1.
The irradiation of N-2-thenoyloxyaryl-4-tert-butylphenoxyacetamides in their molecular film states at 254 nm was found to selectively afford the corresponding photo-Fries rearranged products. This rearrangement reaction was also found to lead to a large increase in the refractive indices of the films, which ranged from 0.021 to 0.035.