Fine tuning of MLCT states in new mononuclear complexes of ruthenium(II) containing tris(1-pyrazolyl)methane, 2,2′-bipyridine and aromatic nitrogen heterocycles

The syntheses of new mononuclear ruthenium(II) complexes of the type: [Ru(bpy)(L)(tpm)](PF6)2 {tpm = tris(1-pyrazolyl)-methane; bpy = 2,2′-bipyridine; L = pz (pyrazine; 1), 4,4′-bpy (4,4′-bipyridine; 2), and bpe [trans-1,2-bis(4-pyridyl)ethylene; 3]} are described, together with their spectroscopic, electrochemical, and photophysical properties. A complete assignment of the NMR resonances of the three species could be made in CD3CN by bidimensional techniques. A fine tuning of the energies of MLCT (metal-to-ligand charge transfer) states in these complexes is disclosed when comparing, in CH3CN, the values of their maximum absorption wave-lengths for the most intense visible bands (λ max) and their redox potentials for the RuIII/Ru II couples; this effect, relevant to the design of efficient photocatalysts, can be attributed to a decreasing order of dπ(Ru) →*(2,2′-bpy) backbonding when decreasing the distance between both N atoms in the aromatic nitrogen heterocycle L that acts in a monodentate manner. Only the species with L = bpe emits at room temperature, pointing to the conclusion that MLCT excited states in this series become higher in energy than dd excited states when the value of λmax is lower than 400 nm. These species are also useful building blocks for new dinuclear mixed-valent complexes. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.Fil: Katz, Néstor Eduardo. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; ArgentinaFil: Romero, Isabel. Universidad de Girona; EspañaFil: Llobet, Antoni. Universidad de Girona; EspañaFil: Parella, Teodor. Universitat Autònoma de Barcelona; EspañaFil: Benet Buchholz, Jordi. Bayer Industry Services; Alemani

Quantitative wave function analysis for excited states of transition metal complexes

The character of an electronically excited state is one of the most important descriptors employed to discuss the photophysics and photochemistry of transition metal complexes. In transition metal complexes, the interaction between the metal and the different ligands gives rise to a rich variety of excited states, including metal-centered, intra-ligand, metal-to-ligand charge transfer, ligand-to-metal charge transfer, and ligand-to-ligand charge transfer states. Most often, these excited states are identified by considering the most important wave function excitation coefficients and inspecting visually the involved orbitals. This procedure is tedious, subjective, and imprecise. Instead, automatic and quantitative techniques for excited-state characterization are desirable. In this contribution we review the concept of charge transfer numbers---as implemented in the TheoDORE package---and show its wide applicability to characterize the excited states of transition metal complexes. Charge transfer numbers are a formal way to analyze an excited state in terms of electron transitions between groups of atoms based only on the well-defined transition density matrix. Its advantages are many: it can be fully automatized for many excited states, is objective and reproducible, and provides quantitative data useful for the discussion of trends or patterns. We also introduce a formalism for spin-orbit-mixed states and a method for statistical analysis of charge transfer numbers. The potential of this technique is demonstrated for a number of prototypical transition metal complexes containing Ir, Ru, and Re. Topics discussed include orbital delocalization between metal and carbonyl ligands, nonradiative decay through metal-centered states, effect of spin-orbit couplings on state character, and comparison among results obtained from different electronic structure methods.Comment: 47 pages, 19 figures, including supporting information (7 pages, 1 figure

Sensitivity of the photo-physical properties of organometallic complexes to small chemical changes

We investigate an effective model Hamiltonian for organometallic complexes that are widely used in optoelectronic devices. The two most important parameters in the model are $J$, the effective exchange interaction between the $\pi$ and $\pi^*$ orbitals of the ligands, and $\epsilon^*$, the renormalized energy gap between the highest occupied orbitals on the metal and on the ligand. We find that the degree of metal-to-ligand charge transfer (MLCT) character of the lowest triplet state is strongly dependent on the ratio $\epsilon^*/J$. $\epsilon^*$ is purely a property of the complex and can be changed significantly by even small variations in the complex's chemistry, such as replacing substituents on the ligands. We find that that small changes in $\epsilon^*/J$ can cause large changes in the properties of the complex, including the lifetime of the triplet state and the probability of injected charges (electrons and holes) forming triplet excitations. These results give some insight into the observed large changes in the photophysical properties of organometallic complexes caused by small changes in the ligands.Comment: Accepted for publication in J. Chem. Phys. 14 pages, 9 figures, Supplementary Info: 15 pages, 17 figure

Near-Infrared and Visible Photoactivation to Uncage Carbon Monoxide from an Aqueous-Soluble PhotoCORM.

Multiphoton excitation allows one to access high energy excited states and perform valuable tasks in biological systems using tissue penetrating near-infrared (NIR) light. Here, we describe new photoactive manganese tricarbonyl complexes incorporating the ligand 4'-p-N,N-bis(2-hydroxyethyl)amino-benzyl-2,2':6',2″-terpyridine (TPYOH), which can serve as an antenna for two photon NIR excitation. Solutions of Mn(CO)3(TPYOH)X (X = Br- or CF3SO3-) complexes are very photoactive toward CO release under visible light excitation (405 nm, 451 nm). The same responses were also triggered by multiphoton excitation at 750 and 800 nm. In this context, we discuss the potential applications of these complexes as visible/NIR light photoactivated carbon monoxide releasing moieties (photoCORMs). We also report the isolation and crystal structures of the TPYOH complexes Mn(TPYOH)Cl2 and [Mn(TPYOH)2](CF3SO3)2, to illustrate a possible photolysis product(s)

Hybrid plasmonic photoreactors as visible light-mediated bactericides

Photocatalytic compounds and complexes, such as tris(bipyridine)ruthenium(II), [Ru(bpy)3]2+, have recently attracted attention as light-mediated bactericides that can help to address the need for new antibacterial strategies. We demonstrate in this work that the bactericidal efficacy of [Ru(bpy)3]2+ and the control of its antibacterial function can be significantly enhanced through combination with a plasmonic nanoantenna. We report strong, visible light-controlled bacterial inactivation with a nanocomposite design that incorporates [Ru(bpy)3]2+ as a photocatalyst and a Ag nanoparticle (NP) core as a light-concentrating nanoantenna into a plasmonic hybrid photoreactor. The hybrid photoreactor platform is facilitated by a self-assembled lipid membrane that encapsulates the Ag NP and binds the photocatalyst. The lipid membrane renders the nanocomposite biocompatible in the absence of resonant illumination. Upon illumination, the plasmon-enhanced photoexcitation of the metal-to-ligand charge-transfer band of [Ru(bpy)3]2+ prepares the reactive excited state of the complex that oxidizes the nanocomposite membrane and increases its permeability. The photooxidation induces the release of [Ru(bpy)3]2+, Ag+, and peroxidized lipids into the ambient medium, where they interact synergistically to inactivate bacteria. We measured a 7 order of magnitude decrease in Gram-positive Arthrobacter sp. and a 4 order of magnitude decrease in Gram-negative Escherichia coli colony forming units with the photoreactor bactericides after visible light illumination for 1 h. In both cases, the photoreactor exceeds the bactericidal standard of a log reduction value of 3 and surpasses the antibacterial effect of free Ag NPs or [Ru(bpy)3]2+ by >4 orders of magnitude. We also implement the inactivation of a bacterial thin film in a proof-of-concept study.Accepted manuscrip