Jean-Claude Chambron

Synthesis and study of a mixed-ligand ruthenium(II) complex in its ground and excited states: bis(2,2′-bipyridine)(dipyrido[3,2-a : 2′,3′-c]phenazine-N4N5)ruthenium(II)

The ruthenium (II) complex [Ru(bipy)2(dppz)]2+(bipy = 2,2′-bipyridine, dppz = dipyrido[3,2-a : 2′,3′-c]phenazine) was synthesized, characterized, and studied. Its oxidation and first reduction potentials are respectively 1.24 and –1.02 V (vs. saturated calomel electrode). The maxima of the metal-to-ligand charge-transfer absorption and emission occur respectively at 448 and 610 nm. These data suggest that [Ru(bipy)2(dppz)]2+ is made up of two electronically independent units, one behaving as a [Ru(bipy)3]2+-like chromophore, the other as a phenazine-like electron acceptor. Excited-state absorption spectra were obtained for [Ru(bipy)2(dppz)]2+ and its parent complex [Ru(bipy)3]2+. Above 500 nm the latter shows only one maximum (at 510 nm), and the former shows two maxima (around 526 and 557 nm), whereas radical anions of both bipyridine and phenazine or dipyridophenazine show two maxima (at 512 and 552 nm for phenazine). In the case of [Ru(bipy)2(dppz)]2+ these results can be interpreted in terms of a light-induced directed charge transfer from the ruthenium to the phenazine part of the dipyridophenazine ligand, and its localization on this ligand moiety. Photochemical properties of [Ru(bipy)2(dppz)]2+ were studied in ethanol. The excited state of the complex is quenched both by an electron acceptor (methylviologen, kq= 1.37 × 109 dm3 mol–1 s–1) and an electron donor (triethanolamine, kq= 4.40 × 107 dm3 mol–1s–1).

Rotaxanes as new architectures for photoinduced electron transfer and molecular motions

Rotaxanes are molecular architectures ideally suited for building integrated, multicomponent modular systems, displaying novel chemical and physical properties. In this new field of functional rotaxanes, those incorporating transition metals, which are incidentally used as synthetic templates, are particularly attractive for their photophysical and electronic properties as well as their dynamic behaviour. It is believed that they will provide, in the future, the basic elements for constructing nanoscale machines and motors.

Supramolecular Chemical Sensors Based on Pyrene Monomer-Excimer Dual Luminescence

The past ten years have seen a spectacular development of chemical sensors based on the monomer-excimer dual luminescence of aromatic systems, such as pyrene. Either in the form of integrated or multicomponent molecular devices these chemosensors have been attracting a high interest above all because of their unique ratiometric properties. This review will focus on the latter systems, which can be classified into two classes: Firstly, the assembly of receptor-effector conjugates is triggerred by the analyte of interest. As a result, the sensor shows monomer to excimer fluorescence switching upon substrate binding. Secondly, the supramolecular assembly that constitutes the sensor is perturbed by interaction with the analyte. This induces a conformational change or the exchange of a component of the system, which is the cause of the luminescence switch effect.

Functional Rotaxanes: From Controlled Molecular Motions to Electron Transfer Between Chemically Nonconnected Chromophores

Considered only laboratory curiosities when first synthesized in the late sixties, rotaxanes (a cyclic component threaded onto a dumbbell-shaped linear component) are now relatively easily available through template synthesis. This has led to the development of functional rotaxanes, for example rotaxanes displaying electrochemically or photochemically triggered intramolecular motions like translation of the ring along the dumbbell, or electron transfer between their mechanically linked components (figure).

Ru (bipy)2dppz2+ : a highly sensitive luminescent probe for micellar sodium dodecyl sulfate solutions

Abstract The luminescence of Ru(bipy) 2 dppz 2+ (dppz is dipyrido [3,2-a:2′,3′-c]phenazine) was previously shown to be totally quenched in water solutions, whereas the complex is luminescent in organic solvents. In sodium dodecyl sulfate aqueous solutions, this complex luminesces strongly above the critical micellar concentration. This latter result correlates well with the observations in alcoholic solvents with long alkyl chains. It is interpreted in terms of the shielding of the dipyridophenazine ligand (at which quenching of the emission occurs) from the water molecules by the micellar core.

Tuning the mechanism of DNA cleavage photosensitized by ruthenium dipyridophenazine complexes by varying the structure of the two non intercalating ligands

The influence of the nature of ligands on the efficiency of ruthenium complexes for photosensitizing DNA cleavage was investigated. Ru(bipy)2dppz2+ and Ru(bpz)2dppz2+ were selected as DNA breakers on the basis of their high affinity for DNA due to the presence of a dppz ligand which can partially intercalate in the major groove of DNA. Their photosensitizing properties were compared to those of Ru(bipy)3(2+), a complex which binds to DNA with a far lower constant. Upon irradiation, these complexes promoted the formation of single strand breaks in supercoiled phi X 174 DNA. Unexpectedly, Ru(bipy)2dppz2+ was found to be less efficient than Ru(bipy)3(2+) whatever the dye concentration or the [base pair]/[Ru] molar ratio r. Scavenging experiments have shown that the oxidative DNA cleavage induced by Ru(bipy)2dppz2+ mainly results from a Type II mechanism. The behavior of Ru(bipy)2dppz2+ was different: this compound was clearly more efficient than Ru(bipy)3(2+) as DNA breaker and its efficiency was not modified by the presence of oxygen or by addition of scavengers of reactive oxygen species. In this case, a mechanism involving electron transfer between the excited state of the ruthenium complex and the guanine residue was proposed in agreement emission lifetime measurements. The change in mechanism observed between Ru(bipy)2dppz2+ and Ru (bipy)2dppz2+ results from an increase of the reduction potential of the ruthenium complexes in the excited state, which appears to be the main factor controlling the efficiency.

Ion‐Pair‐Mediated Asymmetric Synthesis of a Configurationally Stable Mononuclear Tris(diimine)–Iron(II) Complex

Configurational stability is conferred on the complex 1 (R=4-MeOC6H4) by the carefully designed tetradentate bis(1,10-phenanthroline) ligand. The resolution and asymmetric synthesis of 1 were readily achieved by using tris(tetrachlorobenzenediolato)phosphate(V) anions (2) as chiral auxiliaries. The picture shows the separation of the enantiomers of 1 by preparative ion-pair thin-layer chromatography.

A copper(I) [2]-catenate incorporating a tetrathiafulvalene unit

Abstract A copper(I) [2]-catenate incorporating an electron-donor tetrathiafulvalene unit has been synthesized and characterized.

Transition metals as assembling and templating species: From catenanes and knots to organized multi-porphyrins arrays

Absrrucr. New dicopper(1) knots have been synthesized as well as their face-to-face isomers. The knots range from 80 to 90-membered rings and their preparation yields depend crucially on structural parameters such as number of methylene fragments linking the two chelating units and length of the polyethyleneoxy unit used in the cyclization reaction. The best yield was obtained for an 84-membered knotted ring with a -(CH2)6connector : this relatively long fragment allows pronounced winding of the double helix precursor and is thus favorable to the knotting reaction. The X-ray structures of two dicopper trefoil knots are also presented and discussed. The transition metal-directed threading of a molecular fragment containing a central chelate and an end-attached gold(II1) porphyrin into a presynthesized coordinating ring affords a general precursor to a rotaxane-type structures. After threading, construction of the second porphyrin acting as an efficient stopper affords a copper(1) complexed [2]-rotaxane as well as a novel compartmental [3]-rotaxane.

ROTAXANES AND OTHER TRANSITION METAL-ASSEMBLED PORPHYRIN ARRAYS FOR LONG-RANGE PHOTOINDUCED CHARGE SEPARATION

Abstract Bis-porphyrin conjugates have been synthesized for performing long-range photoinduced charge separation. The electron donor is a zinc(II) porphyrin in the excited state and the electron acceptor is a gold(III) porphyrin. These elements or their free-base analogs have been assembled following two different strategies. In a first approach, the porphyrinic subunits, separated by one or more 2,9-diphenyl-1,10-phenanthroline spacers, have been incorporated into rotaxane structures containing up to four threaded macrocycles by copper(I) templated synthesis. In a second approach, a triad having strictly controlled geometry has been prepared following a new gathering strategy. This triad, consisting of two porphyrinic moieties assembled via a central bis(phenyl-terpyridine)ruthenium(II) complex, uses coordination rather than covalent chemistry to interconnect the components.