Jean-Paul Collin

A family of luminescent coordination compounds: iridium(III) polyimine complexes

30 years of IrIII coordination chemistry with polyimine-type ligands are summarized. Over the years, milder reaction conditions have been used for their synthesis, allowing the incorporation of various functional substituents. Complexes are described with bidentate and terdentate ligands, with both N- and C-donor sites. All complexes are luminescent, with predominantly charge-transfer or ligand-centred emissive states depending on the charge density donated from the ligands to the metal. IrIII excited state lifetimes range from nanoseconds to microseconds. A wide range of properties are obtained: [IrN6]3+ complexes are strong photooxidants while tris-cyclometallated [IrN3C3] complexes are strong photoreductants.

Iridium Terpyridine Complexes as Functional Assembling Units in Arrays for the Conversion of Light Energy

In photosynthesis, sunlight energy is converted into a chemical potential by an electron transfer sequence that is started by an excited state and ultimately yields a long-lived charge-separated state. This process can be reproduced by carefully designed multicomponent artificial arrays of three or more components, and the stored energy can be used to oxidize or reduce molecules in solution, to inject electrons or holes, or to create an electron flow. Therefore, the process is important both for artificial-photosynthesis research and for photovoltaic and optoelectronic applications. Molecular arrays for photoinduced charge separation often use chromophores that resemble the natural ones. However, new synthetic components, including transition metal complexes, have had some success. This Account discusses the use of bis-terpyridine (tpy) metal complexes as assembling and functional units of such multicomponent arrays. M(tpy)2(n+) complexes have the advantage of yielding linear arrays with unambiguous geometry. Originally, Ru(tpy)2(2+) and Os(tpy)2(2+) were used as photosensitizers in triads containing typical organic donors and acceptors. However, it soon became evident that the relatively low excited state of these complexes could act as an energy drain of the excited state of the photosensitizer and, thus, seriously compete with charge separation. A new metal complex that preserved the favorable tpy geometry and yet had a higher energy level was needed. We identified Ir(tpy)2(3+), which displayed a higher energy level, a more facile reduction that favored charge separation, a longer excited-state lifetime, and strong spectroscopic features that were useful for the identification of intermediates. Ir(tpy)2(3+) was used in arrays with electron-donating gold porphyrin and electron-accepting free-base porphyrins. A judicious change of the free-base porphyrin photosensitizer with zinc porphyrin allowed us to shape the photoreactivity and led to charge separation with unity yield and a lifetime on the order of a microsecond. In a subsequent approach, an Ir(tpy)2(3+) derivative was connected to an amine electron donor and a bisimide electron acceptor in an array 5 nm long. In this case, the complex acted as photosensitizer, and long-lived charge separation over the extremities (>100 micros, nearly independent of the presence of oxygen) was achieved. The efficiency of the charge separation was modest, but it was improved later, after a modification aiming at decoupling the donor and photosensitizer components. This study represents an example of how the performances of an artificial photofunctional array can be modeled by a judicious design assisted by a detailed knowledge of the systems.

PHOTOINDUCED PROCESSES IN MULTICOMPONENT ARRAYS CONTAINING TRANSITION METAL COMPLEXES

Abstract The authors’ recent activity in the study of photoinduced energy and electron transfer in linear arrays containing porphyrins assembled around a Ru(II) ion, is reviewed. The effect of substituents and distance and the role of the heavy metal ion is discussed. The photophysical and electrochemical properties of Ir(III) terpyridine complexes indicate that Ir(III) ion is a good candidate to successfully replace Ru(II) in the construction of multiporphyrinic linear arrays to achieve efficient photoinduced electron transfer. Preliminary results on multi-porphyrinic systems based on Ir(III) bis-terpyridine are presented.

Electrochemically driven sequential machines: an implementation of copper rotaxanes.

We propose to use the redox states and ligand reorganization characteristics of a copper rotaxane mechanical machine to realize a finite-state machine, that is, a logic machine that possesses an integral memory unit. These compounds provide two definite advantages for the implementation of finite-state set–reset machines: 1) A large ligand reorganization when the redox state of the Cu ion changes, which leads to a clear and reliably observable molecular hysteresis and 2) a rate of reorganization comparable to the voltage sweep rate in cyclic voltammetry. We provide concrete experimental results and a simulation as proof of the principle of the operation of an all-electrochemical-cyclable finite-state machine. Catenanes and rotaxanes constitute an important class of artificial motors based on transition-metal complexes. In view of their proposed applications as logic machines, the rate of mechanical motion is an important factor and depends on the nature of the movement. 13] We have recently reported fast motors based on single-copper dynamic rotaxanes, which can pirouette between two positions around the axle on a millisecond timescale. The rotaxane is made of an axle that consists of a bidentate (2,2’-bipyridine) chelate ligand with two bulky stopper groups and a ring or wheel containing a bidentate 1,10phenantroline and a tridendate (terpyridine) binding site to which the copper ion can bind (see Figure 1). The electro-

A [3]Rotaxane with Two Porphyrinic Plates Acting as an Adaptable Receptor

Following a multistep procedure, the copper(I)-templated strategy allowed preparation of a multifunctional [3]rotaxane. The dumbbell consists of a central two-bidentate chelate unit and two terminal stoppers. The two rings threaded on the rotaxane axis consist each of a 1,10-phenanthroline-incorporating macrocycle, rigidly connected to an appended zinc-complexed porphyrin. The copper(I) template can be removed, affording a free rotaxane whose two rings can glide freely along the axis and spin around it. The dumbbell being very long (approximately 85 A in its extended conformation from one stopper to the other), the porphyrin-porphyrin distance can be varied over a wide range. The two porphyrinic plates constitute the key elements of a receptor able to complex various guests between the plates. The ability of the threaded rings to move freely makes the host perfectly adjustable, allowing capture of geometrically very different guests. The copper(I)-complexed rotaxane also acts as an efficient receptor, although its adaptability is obviously more limited than that of its free rotaxane counterpart.

Templated Synthesis of Cyclic [4]Rotaxanes Consisting of Two Stiff Rods Threaded through Two Bis-macrocycles with a Large and Rigid Central Plate as Spacer

Two related cyclic [4]rotaxanes consisting of double macrocycles and rigid rods incorporating two bidentate chelates have each been prepared in high yield. The first step is a multigathering and threading reaction driven by coordination of two different bidentate chelates (part of either the rings or the rods) to each copper(I) center so as to afford the desired precursor. In both cases, the assembly step is done under very mild conditions, and it is quantitative. The second key reaction is the stopper-attaching reaction, based on click chemistry. Even if the quadruple stoppering reaction is not quantitative, it is relatively high-yielding (60% and 95%), and the copper-driven assembly process is carried out at room temperature without any aggressive reagent. The final copper-complexed [4]rotaxanes obtained contain two aromatic plates roughly parallel to one another located at the center of each bis-macrocycle. In the most promising case in terms of host-guest properties, the plates are zinc(II) porphyrins of the tetra-aryl series. The compounds have been fully characterized by various spectroscopic techniques ((1)H NMR, mass spectrometry, and electronic absorption spectroscopy). Unexpectedly, the copper-complexed porphyrinic [4]rotaxane could be crystallized as its 4PF(6)(-) salt to afford X-ray quality crystals. The structure obtained is in perfect agreement with the postulated chemical structure of the compound. It is particularly attractive in terms of symmetry and molecular aesthetics. The distance between the zinc atoms of the two porphyrins is 8.673 A, which is sufficient to allow insertion between the two porphyrinic plates of small ditopic basic substrates able to interact with the central porphyrinic Zn atoms. This prediction has been confirmed by absorption spectroscopy measurements in the presence of various organic substrates. However, large substrates cannot be introduced in the corresponding recognition site and are thus complexed mostly in an exo fashion, being located outside the receptor cavity. Noteworthy, the stability constants of the 1:1 host-guest complexes are high (10(7) M(-1)).

Long-range coupling in a mixed-valence diruthenium complexes containing bis-terpyridine ligands of various lengths as bridges

Dinuclear ruthenium(II) complexes have been prepared which contain back-to-back bis-terpyridine ligands of various lengths (Ru ⋯ Ru distances between 7 and 20 A) as bridges; significant electronic coupling is observed in mixed-valence states, even for the system with the longest separation.

Efficient and Selective Photochemical Labilization of a Given Bidentate Ligand in Mixed Ruthenium(II) Complexes of the Ru(phen)2L2+ and Ru(bipy)2L2+ Family (L = Sterically Hindering Chelate)

Mixed ruthenium(II) complexes containing 1,10-phenanthroline (or 2,2′-bipyridine) and a sterically congested bidentate ligand such as 2,9-diphenyl-1,10-phenanthroline, 6,6′-dimethyl- or 6,6′-diphenyl-2,2′-bipyridine, or 1-(2′-pyridyl)-3,5-dimethylpyrazole undergo clean and selective ligand substitution under irradiation with visible light. For instance, Ru(phen)2(dmbp)2+ in CH3CN is quantitatively converted to Ru(phen)2(CH3CN)22+ in a photochemical reaction accompanied by expulsion of the sterically hindering chelate dmbp (phen = 1,10-phenanthroline; dmbp = 6,6′-dimethyl-2,2′-bipyridine). Interestingly, 2,2′-bipyridine was found to be photochemically ejected in one case, probably as a consequence of its greater flexibility.

A room temperature luminescent cyclometallated ruthenium(II) complex of 6-phenyl-2,2'-bipyridine

Abstract The cyclometallated complex Ru(tt)(phbp) + (tt=4′-tolyl-2,2′:6′2″-terpyridine, phbp=6-phenyl-2,2′-bipyridine) with a (N,N,N)(C,N,N) coordination, has been synthesized and characterized by 1 H NMR, UV, FAB-MS spectral techniques and by elemental analysis. We have compared its electrochemical and photophysical properties with those of the non-orthometallated analogues Ru(tt) 2 2+ and Ru(terpy) 2 2+ (terpy=2,2′:6′,2″-terpyridine). The most remarkable feature of Ru(tt)(phbp) + is its ability to luminesce at room temperature in alcoholic and nitrile solvents. The lifetime of its 3 MLCT excited state is 60 ns in CH 3 CN.

Electrochemical and Spectroscopic Properties of Cyclometallated and Non-Cyclometallated Ruthenium(II) Complexes Containing Sterically Hindering Ligands of the Phenanthroline and Terpyridine Families

Two series of cyclometallated and noncyclometallated ruthenium(II) complexes incorporating mono- or disubstituted 1,10-phenanthroline- and 2,2′:6′,2′′-terpyridine-type ligands have been synthesized and characterized. An X-ray crystal structure for one of the complexes, Ru(ttpy)(mapH)-(Cl)(PF6), has been obtained (mapH = 2-p-anisyl-1,10-phenanthroline; ttpy = 4′-tolyl-2,2′:6′,2′′-terpyridine). Distinct electrochemical and photophysical properties have been observed for the two series: a remarkable feature is the observation of relatively long-lived MLCT excited states (from 70 to 106 ns at room temperature in CH3CN) for three of the cyclometallated complexes. A discussion is given on the role of factors like sigma donation by the cyclometallating ligands, interligand steric hindrance and interligand π-π interactions that affect the electrochemical and spectroscopic properties.