Bis-cyclometalated cationic iridium (Ir) complexes 1-4 comprising two 2-(2-pyridyl)benzo[b]thiophene (btp) ligands and one 2,2'-bipyridyl (bpy) ancillary ligand with different substituents were prepared as new visible light-absorbing sensitizers and examined for their photophysical and electrochemical properties. Complex 1 was prepared as a parent complex without any substituents. Complexes 2-4 contained methyl-, methoxy-, and trifluoromethyl groups at 4,4'-positions on the bpy ancillary ligand. Systematic investigation of these complexes revealed that such a simple chemical modification selectively controls the excited-state lifetime, while the absorption and emission spectral features remain unchanged. Specifically, the phosphorescence lifetimes of complexes 2 and 3 with electron-donating groups (τ = 3.50 μs, 3.90 μs) were found to be much longer than that of complex 1 (τ = 0.273 μs), and complex 4, possessing strong electron-withdrawing trifluoromethyl groups, did not exhibit detectable phosphorescence at room temperature. The large differences in excited-state lifetimes of complexes 1-3, as well as the nonemissive character of complex 4, are attributed to a strong influence of the substituents on the ligand field strength. The increased σ-donating ability of the ancillary ligand in complexes 2 and 3 destabilizes a short-lived, nonemissive triplet metal-centered ((3)MC) state and increases the energy separation between the (3)MC state and emissive triplet ligand-centered ((3)LC) state based on the btp ligand. For complex 4, however, the (3)MC state is close in energy to the (3)LC state because of the decreased σ-donating ability of the ancillary ligand. Additional evidence of the (3)MC state associated with the changeable excited state was also provided via low-temperature phosphorescence measurements and density functional theory calculations. Ir complexes 1-4 were tested as sensitizers in photoinduced electron-transfer reaction of triethanolamine and methylviologen chloride (MVCl2). As a result, complexes 2 and 3 exhibited much better photosensitizing property compared to complex 1 since their long-lived excited states promoted an oxidative quenching pathway. This Study has first demonstrated that simple substitution on the diimine ancillary ligand can control the (3)MC state of the bis-cyclometalated cationic Ir complex to finely tune the excited-state lifetime and photosensitizing property.

A series of monomeric Ru II complexes [Ru(bda)(pyR) 2 ] (H 2 bda = 2,2Ј-bipyridine-6,6Ј-dicarboxylic acid, pyR = pyridine with a substituent R at the 4-position) were prepared, and the effects of substituent groups on the pyridine ligands of the complexes on catalytic activities toward water oxidation, as well as on photophysical and electrochemical properties, were examined. An increase in the electron-withdrawing ability of the substituent results in a redshift of the absorption maximum assigned to the transition from the d orbital of Ru to the π* orbitals of the pyridine ligands, and an increase in the oxidation potential of the complex. These results are reasonably explained in terms of the variation of the energy level of molecular orbitals induced by the substituent group, which is supported by density functional theory [a]

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Background and Aims: Mesocentrotus nudus is commercially harvested from shallow rocky bottoms in northern Japan. The gonads are targeted as an edible product. The objective of this study was to identify odor-active volatile organic compounds (VOCs) from the gonads of adult M. nudus collected at a fishing ground in Miyagi Prefecture, Tohoku, Japan. Methods and Results: Gas chromatography-mass spectrometry analysis and gas chromatography-sniffing techniques identified 42 compounds categorized as alcohols, aldehydes, aromatic hydrocarbons, esters, halomethanes, hydrocarbons, ketones, sulfur-containing compounds, and nitrogen-containing compounds. GC-sniffing analysis characterized four compounds with preferable odors of sea urchin gonads; limonene, propyl acetate, acetone, dibromochloromethane. On the other hand, the analysis characterized three compounds with unpreferable odors; methyl mercaptane, dimethyl sulfide, and s-methyl thioacetate. Several VOCs from the gonads were derived from seaweeds, terrestrial plants, and fish flesh as food because M. nudus is omnivorous. Conclusion: This is the first study to identify VOCs from edible sea urchin gonads in the wild in Japan. These VOC data comprise a typical standard in order to evaluate a higher quality of sea urchin gonads.