Since the initial report by Lehn et al. in 1979, ruthenium tris(bipyridine) ([Ru(bpy) 3 ] 2+ ) and its numerous derivatives were applied as photosensitizers (PSs) in a large panel of photocatalytic conditions while the bis(terpyridine) analogues were disregarded because of their low quantum yields and short excited-state lifetimes. In this study, we prepared a new terpyridine ligand, 4′-(4-bromophenyl)-4,4‴:4″,4‴′-dipyridinyl-2,2′:6′,2″-terpyridine (Bipytpy) and used it to prepare the heteroleptic complex [Ru(Tolyltpy)(Bipytpy)](PF 6 ) 2 (1; Tolyltpy = 4′tolyl-2,2′:6′,2′-terpyridine). Complex 1 exhibits enhanced photophysical properties with a higher quantum yield (7.4 × 10 -4 ) and a longer excited-state lifetime (3.8 ns) compared to those of [Ru(Tolyltpy) 2 ](PF 6 ) 2 (3 × 10 -5 and 0.74 ns, respectively). These enhanced photophysical characteristics and the potential for PS-catalyst interaction through the peripheral pyridines led us to apply the complex for visible-light-driven hydrogen evolution.The photocatalytic system based on 1 as the PS, triethanolamine as a sacrificial donor, and cobaloxime as a catalyst exhibits sustained activity over more than 10 days under blue-light irradiation (light-emitting diode centered at 450 nm). A maximum turnover number of 764 was obtained after 12 days.

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The photocatalytic reduction of water to form hydrogen gas (H 2 ) is a promising approach to collect, convert, and store solar energy. Typically, ruthenium tris(bipyridine) and its many derivatives are used as photosensitizers (PSs) in a variety of photocatalytic conditions. The bis(terpyridine) analogues, however, have only recently gained attention for this application because of their poor photophysical properties. Yet, by the introduction of electron-donating or -withdrawing groups on the terpyridine ligands, the photophysical and electrochemical properties can be considerably improved. In this study, we report a series of nonsymmetric 2,6-di(pyridin-2yl)pyrimidine ligands with peripheral pyridine substituents in different positions and their corresponding ruthenium(II) complexes. The presence of the pyrimidine ring stabilizes the lowest unoccupied molecular orbital, leading to a red-shifted emission and prolonged excited-state lifetimes as well as higher luminescence quantum yields compared to analogous terpyridine complexes. Furthermore, all complexes are easier to reduce than the previously reported bis(terpyridine) complexes used as PSs. Interestingly, the pyridine substituent in the 4-pyrimidine position has a greater impact on both the photophysical and electrochemical properties. This correlation between the substitution pattern and properties of the complexes is further investigated by using time-dependent density functional theory. In hydrogen evolution experiments under blue-and red-light irradiation, all investigated complexes exhibit much higher activity compared to the previously reported ruthenium(II) bis(terpyridine) complexes, but none of the complexes are as stable as the literature compounds, presumably because of an additional decomposition pathway of the reduced PS competing with electron transfer from the reduced PS to the catalyst.

Iron disulphide molten salt electrochemical cells are among the most promising technological options for batteries. The electrochemical behaviour of pyrite allies excellent cathodic characteristics to optimal performance and low operational costs. The cathodic iron disulphide mechanism involves many processes, encompassing from polysulphides formation to the reduction of iron to the metallic state. The use of X-ray diffraction together with scanning electronic microscopy analysis on cells of the Li/KCl-LiCl/FeS 2 system made possible to identify intrinsic and extrinsic parameters to the electrochemical process involved in the establishment of the polysulphides stoichiometry. It is necessary to note that the augmentation of the cell's internal resistance and loss of electrical capacity are directly related with the formation of these same substances. Researches in the electrochemistry of these phenomena aim to elucidate the cathodic interphase processes and the effect of every reaction in the global mechanism.Keywords: pyrite; molten salts; thermal batteries. IntroduçãoO comportamento eletroquímico da pirita vem apresentando crescente interesse devido as excelentes características catódicas, aliando requisitos de ótima performance e baixos custos operacionais, destacando-se o nível tóxico baixo e a facilidade de obtenção e manuseio. O dissulfeto de ferro pode ser obtido pela purificação da pirita mineral ou por métodos químicos na forma de pó. Nos

In this study, we investigate the impact of N‐methylation on the electronic and photophysical properties of both homoleptic and heteroleptic Ru(II) bis‐terpyridine complexes based on the recently reported ligand 4’‐(4‐bromophenyl)‐4,4’’’ : 4’’,4’’’’‐dipyridinyl‐2,2’ : 6’,2’’‐terpyridine (Bipytpy), with pyridine substituents in the 4‐ and 4’’‐position. The first reduction of the methylated complexes takes place at the pyridinium site and is observed as multi‐electron process. Following N‐methylation, the complexes exhibit higher luminescence quantum yields and longer excited‐state lifetimes. Interestingly, the photophysical properties of the heteroleptic and homoleptic complexes are rather similar. TD‐DFT calculations support the experimental results. Furthermore, the complexes are tested as photosensitizers for photocatalytic hydrogen production, as the parent complex 1 [Ru(Bipytpy)(Tolyltpy)](PF6)2 (Tolyltpy: 4′‐tolyl‐2,2′ : 6′,2′’‐terpyridine) was recently shown to be active and highly stable under photocatalytic conditions. However, the methylated complexes reported herein are inactive as photosensitizers under the chosen conditions, presumably due to loss of the methyl groups, converting them to the non‐methylated parent complexes.