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We report the photophysical and photochemical properties of RuII–polypyridine complexes [Ru(bpy)(dcbpy)py2]2+ (1)2+ and [Ru(dcbpy)2py2]2+ (2)2+ (bpy = 2,2′‐bipyridine, dcbpy = 4,4′‐dicarboxy‐2,2′‐bipyridine, py = pyridine). These complexes combine a monodentate ligand with a chelate bipyridine substituted with carboxylate groups. At low pH, both complexes present metal‐to‐ligand charge transfer absorption bands in the visible region and room‐temperature photoluminescence with long excited‐state lifetimes (τ > 200 ns). At physiological pH, their absorption and emission maxima are displaced to higher energies, with a significant reduction of their emission lifetime. These species show photosubstitution of the monodentate pyridine upon irradiation at 450 nm. At low pH, the quantum yield for this process is very low, but at physiological pH, they are very active, with a φPS,450 value of 0.14 for (1)2+ and of 0.17 for (2)2+. The products of photosubstitution were identified as monoaquo complexes. Both the reactants and the products of the photosubstitution show photoluminescence, but with very different lifetimes, making it possible to monitor the reaction by the time constant of their decay. The ability of complexes (1)2+ and (2)2+ to photorelease monodentate ligands at physiological pH makes them attractive candidates for the delivery of biomolecules linked to more complex structures through the carboxylate functional group. [ABSTRACT FROM AUTHOR]

Multi-metallic complexes based on {Ru–Cr}, {Ru–Ru} and {Ru–Ru–Cr} fragments are investigated for their light-harvesting and long-range energy transfer properties. We report the synthesis and characterization of [Ru(tpy)(bpy)(μ-CN)Ru(py)4Cl]2+ and [Ru(tpy)(bpy)(μ-CN)Ru(py)4(μ-NC)Cr(CN)5]. The intercalation of {RuII(py)4} linked by cyanide bridges between {Ru(tpy)(bpy)} and {Cr(CN)5} results in efficient, distant energy transfer followed by emission from the Cr moiety. Characterization of the energy transfer process based on photophysical and ultrafast time-resolved absorption suggests the delocalization of holes in the excited state, providing a pathway for energy transfer between the end moieties. The proposed mechanism opens the door to utilize this family of complexes as an appealing platform for the design of antenna compounds as the properties of the fragments could be tuned independently. [ABSTRACT FROM AUTHOR]

Ligand field (LF) states have been present in discussions on the photophysics and photochemistry of ruthenium-iminic chromophores for decades, although there is very little documented direct evidence of them. We studied the picosecond transient absorption (TA) spectroscopy of four {RuII(imine)} complexes that respond to the formula trans-[Ru(L)4(X)2], where L is either pyridine (py) or 4-methoxypyridine (MeOpy) and X is either cyanide or thiocyanate. Dicyano compounds behave as most ruthenium polypyridines and their LF states remain silent. In contrast, in the dithiocyanate complexes we found clear spectroscopic evidence of the participation of LF states in the MLCT decay pathway. These states are of donor and acceptor character simultaneously and this is manifested in the presence of MLCT and LMCT transient absorption bands of similar energy. Spectroelectrochemical techniques supported the interpretation of the absorption features of MLCT states, and DFT methods helped to assign their spectroscopic signatures and provided strong evidence on the nature of LF states. [ABSTRACT FROM AUTHOR]

This manuscript addresses the synthesis, structural characterization and optical properties of a 1D coordination polymer (CPs) and 2D and 3D Metal–Organic Frameworks (MOFs) obtained from lanthanide metals, 3-hydroxinaftalene-2,7-disulfonic acid (3-OHNDS) and two different phenanthroline derivates as ancillary ligands. The first is a family of 2D compounds with formula [Ln(3-OHNDS)(H2O)2], where Ln = La(1), Pr(2), Nd(3) and Sm(4). The addition of 1,10-phenanthroline (phen) in the reaction produces 1D compounds with general formula [Ln(3-OHNDS)(phen)(H2O)]·3H2O, where Ln = La(5), Pr(6), Nd(7) and Sm(8). Finally, the synthesis with 3,4,7,8-tetramethyl-1,10-phenanthroline (3,4,7,8-TMPhen) as an ancillary ligand results in the formation of the 3D [La(3-OHNDS)(3,4,7,8-TMphen)(H2O)] (9) compound. The photoluminescence (PL) properties of 1D and 2D compounds were fully investigated in comparison with the 3-OHNDS ligand. One of the most important results was the obtaining of a white-light single-emitter without adding dopant atoms in the structure. With all these results in mind it was possible to establish structure–property relationships. [ABSTRACT FROM AUTHOR]

We report the synthesis, crystal structure, electrochemical and spectroscopic properties oftrans-[Ru(MQ)4Cl2]4+(14+), where MQ+ = N-methyl-4,4′-bipyridinium. The crystal structure of14+shows the pyridinic rings bound in atransfashion to the Ru ion. In14+and in its analogtrans-[Ru(4,4′-bpy)4Cl2] (2, bpy = bipyridine), the electrochemical reduction waves of the four iminic ligands occur at very closely spaced potentials. In comparison with previously reported analogues,14+and2present high molar extinction coefficients (ε= 20,000–50,000 M–1cm–1), and red-shifted absorptions (up to 800 nm for14+and up to 600 nm for2) in acetonitrile. Upon protonation of the four exposed nitrogens of2and electrochemical reduction of the ligands in14+and2, spectral changes occur with retention of isosbestic points, revealing the presence of four independent chromophores. These results suggest poor electronic communication between the aromatic ligands within each compound, in contrast to related complexes such ascis-[Ru(2,2′-bpy)2Cl2] (3). [ABSTRACT FROM PUBLISHER]

Ultrafast laser spectroscopy has been used to measure the electron-phonon coupling constant in PtAu core-shell bimetallic nanoparticles. A chemical reduction method was used to prepare Pt cores of 12.5 nm diameter and a γ-radiolytic deposition technique was then used to grow Au shells of variable thickness. The resulting nanoparticles have a spectrum that is characteristic of Au. It is found that the electron-phonon coupling time for these hybrid nanoparticles (τ[sub e-ph]∼200 fs) is over a factor of 3 shorter than that for plain Au nanoparticles (τ[sub e-ph]∼650 fs). The faster dynamical response is due to the large electron-phonon coupling constant for Pt, which provides efficient scattering of the excited electrons. Platinum dominates the temporal response, even for a 1:6 molar ratio of Pt to Au, because it has a much larger density of states near the Fermi level compared to Au. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ultrafast laser experiments were used to study electron-phonon coupling in Au nanoparticles in the 2.5 to 8 nm size range in aqueous solution. The electron-phonon coupling constants for these samples were found to be independent of the particle size. This is attributed to a weak interaction between the electron gas and the surface phonon modes in Au. Calculations were performed which show that the coupling between the hot electrons and the surface accounts for less than 10% of the total electron energy losses for these particles. Thus, bulk electron-phonon coupling dominates the relaxation of excited electrons in Au particles, for particles as small as several hundred atoms. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]