Isabelle M. Dixon

Luminescent ruthenium-polypyridine complexes & phosphorus ligands: anything but a simple story.

This tutorial review presents an exhaustive picture of the luminescence studies that have been undertaken on ruthenium(ii) complexes bearing polypyridine and phosphorus(iii) ligands. The introduction of phosphorus to the Ru coordination sphere has multiple consequences on the nature and energy of the various excited states involved, but it does not necessarily rule out room temperature emission.

Can a functionalized phosphine ligand promote room temperature luminescence of the [Ru(bpy)(tpy)]2+ core?

Unexpected room temperature luminescence is observed and rationalized by highly challenging excited state calculations for a functionalized phosphine ligand coordinated on the [Ru(bpy)(tpy)](2+) core.

Electronic peculiarities of the excited states of [RuN5C]+vs. [RuN6]2+ polypyridine complexes: insight from theory

The ground state, oxidized ground state, (3)MLCT and (3)MC excited states have been studied by DFT and TDDFT for two Ru(II) complexes bearing an N(6) or N(5)C coordination sphere. The effect of replacing one Ru-N dative bond by one Ru-C covalent bond have been studied and quantified on their ground state by the means of geometry optimization, NBO analysis and calculation of their IR vibrations. IR fingerprints of the Ru-C bond have been found at 945 and 1113 cm(-1). In addition, this study confirmed and quantified the effects of N→C(-) substitution on the spectroscopic properties of the [RuN(5)C](+) complex: a broader and bathochromically-shifted absorption spectrum, a smaller ground-(3)MLCT energy gap and a highly energetic (3)MC state are the major characteristics of the carbon-containing monocationic complex.

Is photoisomerization required for NO photorelease in ruthenium nitrosyl complexes

AbstractThe factors that explain the competition between intramolecular NO linkage photoisomerization and NO photorelease in five ruthenium nitrosyl complexes were investigated. By applying DFT-based methods, it was possible to characterize the ground states and lowest triplet potential energy surfaces of these species, and to establish that both photoisomerization and photorelease processes can occur in the lowest triplet state of each species. This work highlights the crucial role of the sideways-bonded isomer, a metastable state also known as the MS2 isomer, in the photochemical loss of NO, while the results obtained also indicate that the population of the triplet state of this isomer is compulsory for both processes and show how photoisomerization and photorelease interfere. Graphical AbstractIllustration of the crucial role of the 3MS2 state in the photoreactivities of ruthenium nitrosyl complexes

Bridging the gap: making the link in mechanically interlocked chiral molecules.

[n]Catenanes are chains of n intertwined rings kept together through a topological link, that is, without any covalent or coordination bonds. The archetype of such molecules is the [2]catenane, in which two rings are mechanically dependent on each other, despite the absence of a bond. These fascinating topological objects can be used as components for nanomachines and nanodevices: the relative motion of the two rings can be controlled by external stimuli such as light, electrons, or metal coordination, and the forward and back processes can be followed by NMR spectroscopy, fluorescence spectroscopy, electrochemistry, or conductivity measurements; circular dichroism spectroscopy can even be used if the catenanes are chiral. In the history of synthetic catenanes, seminal work by the research groups of Sauvage and Stoddart gave access to catenanes on a preparative scale by using a metal template or donor–acceptor interactions (Figure 1). More recently, catenanes built around multiple hydrogen bonds were described by the research groups of Leigh and V gtle. Today, the efficiency of such a template combined with electrostatic interactions is at its best with the optically active catenane reported by Furusho and co-workers. For the first time a salt bridge serves as an assembling motif for the formation of [2]catenanes. This amidinium-carboxylate salt bridge template was previously used by these researchers as they have already used it as a recognition motif for the preparation of a family of double-stranded helical polymers. It is very efficient as a template because it exhibits high association constants even in polar solvents and the double hydrogen bond bridge gives a well-defined geometry to the precursor. In addition, the bridge can be opened or closed by varying the pH value of the medium. The desired catenane was synthesized in a good 68% yield by the now famous ring-closing metathesis (RCM) reaction popularized in the field of molecular topology by Sauvage et al. by using the first generation Grubbs catalyst in the double macrocyclization step. Unfortunately X-ray diffraction could not be used to characterize the catenane directly, but unambiguous proof of the catenated structure was obtained by very clever derivatization studies. Indeed, RCM cyclization of the precatenane can not only form the desired catenane but also the two isolated rings or a large [1+1] macrocycle (Figure 2). The authors were able to exclude the possibility of a 1:1 mixture of the two separated rings by comparison of the H NMR spectra of the catenane and of an equimolar mixture of the two genuinely synthesized separated rings. To exclude the formation of the large macrocycle they studied the degradation products obtained by a transesterification reaction. A close examination of the ESI mass spectrum clearly proved that the degradation compounds experimentally observed could only arise from the catenated structure as shown in Figure 2. Thus, the amidinium-carboxylate salt bridge has served as an efficient template for the formation of the precatenane, and has been maintained throughout the RCM cyclization step. Once the catenated structure was proven, the authors studied the possibility to lock and unlock the two intertwined rings. Reaction with trifluoroacetic acid (TFA) unlocks the bridge, thus allowing free rotation of the two rings with respect to one another. Subsequent addition of iPr2NEt Figure 1. The four different types of templates used for the synthesis of [2]catenanes: metal ion coordination, donor–acceptor interactions, hydrogen bonding, and a salt bridge.

Linkage Photoisomerization Mechanism in a Photochromic Ruthenium Nitrosyl Complex: New Insights from a MS-CASPT2 Study

The N → O linkage photoisomerization mechanism in a ruthenium nitrosyl complex, [RuCl(NO)(py)4]2+, for which a quasicomplete photoconversion between the stable nitrosyl (N-bonded) and metastable isonitrosyl (O-bonded) isomers has been observed under continuous irradiation of the crystal at 473 nm ( Cormary et al. Acta Cryst. B 2009 , 65 , 612 - 623 ), is investigated using multiconfigurational second-order perturbation theory (CASPT2). The results support efficient intersystem crossing pathways from the initially excited singlet states to the lowest triplet excited state of metal-to-ligand charge transfer character (3MLCT). The topology of the involved potential energy surfaces corroborates a complex sequential two-photon photoisomerization mechanism involving nonadiabatic processes in agreement with experimental observations and previous density functional theory calculations.

Exploration of Uncharted 3PES Territory for [Ru(bpy)3]2+: A New 3MC Minimum Prone to Ligand Loss Photochemistry

We have identified a new 3MC state bearing two elongated Ru-N bonds to the same ligand in [Ru(bpy)3]2+. This DFT-optimized structure is a local minimum on the 3PES. This distal MC state (3MCcis) is destabilized by less than 2 kcal/mol with respect to the classical MC state (3MCtrans), and energy barriers to populate 3MCcis and 3MCtrans from the 3MLCT state are similar according to nudged elastic band minimum energy path calculations. Distortions in the classical 3MCtrans, that is, elongation of two Ru-N bonds toward two different bpy ligands, are not expected to favor the formation of ligand-loss photoproducts. On the contrary, the new 3MCcis could be particularly relevant in the photodegradation of Ru(II) polypyridine complexes.