Phenyl-Substituted Cage Silsesquioxane-Based Star-Shaped Giant Molecular Clusters: Synthesis, Properties, and Surface Segregation Behavior.

The crystallinity, solubility, and physical properties of polyhedral oligomeric silsesquioxane (POSS) compounds are highly dependent on their organic substituents. We previously synthesized a series of isobutyl-substituted star-shaped POSS derivatives with aliphatic chain linkers of different length. In this study, we prepared C3- and C6-linked phenyl-substituted star-shaped POSS derivatives (3Ph-C3 and 3Ph-C6) by the hydrosilylation of heptaphenylallyl- and hexenyl-POSS (1a and 1b) and octadimethylsiloxy-Q8-silsesquioxane (Q8M8H) (2), respectively, and their properties were compared with those of the corresponding isobutyl-substituted derivatives (5iBu-C3 and 5iBu-C6). Although 3Ph-C6 was only soluble in chloroform and insoluble in tetrahydrofuran (THF) and toluene, 3Ph-C3 was soluble even in THF and toluene, suggesting that the shorter linkers of the derivative afford a wider range of solvents for dissolution. Differential scanning calorimetry analysis showed that 3Ph-C3 exhibited a baseline shift at 190 °C and an endothermic peak at 316 °C. However, no clear baseline shift was observed for 3Ph-C6. Thermogravimetric analysis showed that the shorter linker in the phenyl-substituted star-shaped POSS derivative significantly increased the decomposition temperature compared with the longer linker. The annealed cast film of 3Ph-C3 at 340 °C above its melting temperature formed a transparent film even after cooling to room temperature. However, an opaque whitish film was formed in the case of 3Ph-C6. Poly(methyl methacrylate) (PMMA) films containing 2 wt % 3Ph-C3 and 3Ph-C6 were prepared by casting their chloroform solutions onto glass substrates overnight at room temperature. The static water contact angle measurements and XPS analysis for the castings film containing 3Ph-C3 and 3Ph-C6 suggested that degree of the segregation amount of 3Ph-C3 was larger than that of 3Ph-C6. The shorter linker length in the phenyl-substituted star-shaped POSS derivative, 3Ph-C3, with its greater predicted solubility in PMMA, exhibited entropy-driven surface segregation.

Electron and hole capture processes in Cu-doped glass exhibiting radiophotoluminescence.

Radiophotoluminescence (RPL) is a radiation effect, and materials exhibiting RPL can be used in dosimeters. In this study, we observed remarkable RPL in Cu-doped aluminoborosilicate and silica glasses upon their exposure to60Coγ-rays. The RPL intensity increased proportionally with the irradiation dose up to several hundreds of grays and then saturated beyond a certain dose level. An equation was derived theoretically to express the relationship between the RPL intensity and irradiation dose based on the RPL mechanism, in which copper ions, Cu2+and Cu+, capture electrons and holes, generated by the irradiation, respectively, resulting in a change in the valence. The equation fitted well with the experimental results, providing two parameters for the equation. These parameters are associated with the saturation dose level and sensitivity, which are important for the application of materials to dosimeters. These parameters were discussed based on electron and hole capture processes in the RPL mechanism.

DFT study of the stereoselective formation of cis-W(CO)4(η2-C2H4)2 in the gas-phase consecutive coordination of C2H4 onto doubly coordinatively unsaturated W(CO)4.

B3LYP-based density functional theory (DFT) calculations are reported that provide insight into the stereoselective formation of cis-W(CO)(4)(η(2)-C(2)H(4))(2) observed in the pulsed 266 nm laser photolysis of tungsten hexacarbonyl (W(CO)(6)) in the presence of C(2)H(4) in the gas phase at room temperature (J. Phys. Chem. 1995, 99, 4558). W(CO)(4)(η(2)-C(2)H(4)) formed through the coordination of C(2)H(4) onto coordinatively unsaturated W(CO)(4) was found to have a pseudo-C(2v) symmetry (distorted trigonal bipyramid with an angle of ca. 90° between the two equatorial COs) with a bond dissociation enthalpy (BDE) of W-C(2)H(4) of 125 kJ mol(-1). In the subsequent coordination of C(2)H(4) onto the W(CO)(4)(η(2)-C(2)H(4)), having one vacant coordinatively unsaturated site, no barrier was found in the reaction path to cis-complex formation, while there was a barrier of about 89 kJ mol(-1) to the trans-complex. The calculations show that the stereoselective formation of cis-W(CO)(4)(η(2)-C(2)H(4))(2) is due to kinetic rather than thermodynamic control. The trans-W(CO)(4)(η(2)-C(2)H(4))(2) was calculated to be more stable than cis-W(CO)(4)(η(2)-C(2)H(4))(2) by about 10 kJ mol(-1). The BDE of W-C(2)H(4) in cis-W(CO)(4)(η(2)-C(2)H(4))(2) was estimated to be 61 kJ mol(-1).