Artificial molecular-level machines with [Ru(bpy)3]2

A molecular-level machine is an assembly of a discrete number of molecular components (that is, a supramolecular structure) designed to perform mechanical-like movements (output) as a consequence of appropriate external stimuli (input). Like macroscopic machines, molecular-level machines are characterized by (i) the kind of energy input supplied to make them work, (ii) the kind of movement performed by their components, (iii) the way in which their operation can be controlled and monitored, (iv) the possibility to repeat the operation at will and establish a cyclic process, (v) the time scale needed to complete a cycle of operation, and (vi) the function performed. The most convenient way to supply energy to an artificial molecular-level machine is through a photochemical reaction.[Ru(bpy)3]2+(bpy=2,2′-bipyridine) can be used as a photosensitizer to power mechanical movements in machines based on pseudorotaxanes, rotaxanes and catenanes. Besides being used as an external photosensitizer,[Ru(bpy)3]2+can be incorporated in one of the machine components as a "light-fueled" motor. Three types of photochemically driven piston/cylinder systems and a photocontrollable molecular abacus are described. Other kinds of more sophisticated molecular-level machines based on rotaxanes and catenanes are proposed. The extension of the concept of machine to the molecular level is important not only for the sake of basic research, but also for the growth of nanoscience and the development of nanotechnology

Photochemical investigation of a photochromic diarylethene compound that can be used as a wide range actinometer

The photochromic diarylethene derivative 1,2-bis(5-(4-ethynylphenyl)-2-methylthiophen-3-yl)perfluorocyclopentene (1) was submitted to photochemical, thermal stability and fatigue resistance studies in acetonitrile, also to evaluate its possible application as a new actinometer. This photochromic system covers a wide spectral absorption range, with intense bands in the UV and visible regions for the open-ring and closed-ring isomers, respectively. Very high ring-closure quantum yield values were obtained, in contrast with the low ring-opening quantum yields, which are nevertheless high enough to exploit 1 as an actinometer. The procedure required to determine the photon flux of an irradiation source with this fatigue resistant compound is indeed very simple

Photoinduced electron flow in a self-assembling supramolecular extension cable

We report the design, bottom-up construction, characterization, and operation of a supramolecular system capable of mimicking the function played by a macroscopic electrical extension cable. The system is made up of a light-powered electron source, an electron drain, and a cable as the molecular components programmed to self-assemble by means of two distinct plug/socket junctions. Such connections are reversible and can be operated independently by orthogonal chemical inputs. In the source-connector-drain supermolecule, photoinduced electron transfer from source to drain occurs, and it can be switched off by dual-mode chemically controlled disassembling of the molecular components.Ferrer Ribera, RB.; Rogez, G.; Credi, A.; Ballardini, R.; Gandolfi, MT.; Balzani, V.; Liu, Y.... (2006). Photoinduced electron flow in a self-assembling supramolecular extension cable. Proceedings of the National Academy of Sciences. 103(49):18411-18416. doi:10.1073/pnas.060645910318411184161034

Photophysical, photochemical and electrochemical properties of a series of aromatic electron acceptors based on N-heterocycles

The electronic absorption and luminescence spectra, photoreactivity, and the electrochemical properties of a series of aromatic electron acceptors based on the 4,4′-bipyridinium, 1,2-bis(4-pyridinium)ethylene, and 2,7-diazapyrenium cations have been investigated. All these species exhibit distinctive absorption spectra and some of them show fluorescence and phosphorescence bands. The compounds based on the 1,2-bis(4-pyridinium)ethylene unit provide the interesting possibility of studying the E–Z photoisomerization of the vinylic double bond. The photophysical and photochemical properties have been also interpreted on the basis of quantum chemical calculations. All the examined compounds exhibit reduction processes at mild negative potentials that reveal their electron accepting character. We found that the photophysical, photochemical and electrochemical properties of such compounds are not only determined by the structure of the N-heterocyclic central moiety, but are also remarkably affected by the peripheral substituents linked to the quaternarized nitrogen atoms

Photochemical, Photophysical and Electrochemical Properties of a Photoisomerizable Cyclophane and its [2]Catenates with Aromatic Crown Ethers

The photochemical, photophysical, and electrochemical behaviour of t-1,2-bis(1-benzy1-4- pyridinium)ethylene (t-DBBPE2+) (used as model compound), a cyclophane made of two t-1,2-bis(4-pyridin-ium)ethylene (BPE) units (141, and its catenanes (1B134+,1BN4+, and INN') with aromatic crown ethers containing two p-dimethoxybenzene units (BB), one p-dimethoxybenzene and one 1,5-dimethoxynaphthalene unit (BN), and two 1,5-dimethoxynaphthalene units (NN) have been investigated in acetonitrile solution. For both t-DBBPE' and 14+, fluorescence and direct trans-*cis photoisomerization are prevented by the presence of an intramolecular charge-transfer (CT) excited state close to or below the lire level, but the triplet-sensitized photoisomerization takes place with high quantum yield. In the 1BB4*, 1BN4', and 1NN4' catenanes, also the triplet sensitized photoisomerization is quenched by the presence of lower lying inter-component CT levels. The intercomponent CT interaction present in the catenanes affects the reduction potentials of the t-DBBPE2+ units of 14+. Such an interaction, which plays the role of a brake against the free rotation of the two rings of catenanes, is released upon reduction of the 14+ cyclophane

Proton Controlled Intramolecular Communication in Dinuclear Ruthenium(II) Polypyridine Complexes

The synthesis and characterization of two dinuclear ruthenium polypyridyl complexes based on the bridging ligands 5,5'-bis(pyridin-2"-yl)-3,3'-bis(1H-1,2,4-triazole) and 5,5'-bis(pyrazin-2"-yl)-3,3'-bis(1H-1,2,4-triazole) and of their mononuclear precursors are reported. The dinuclear compounds have been prepared by a Ni(0) catalyzed coupling of a mononuclear ruthenium(II) polypyridyl complex containing a brominated triazole moiety. Electrochemical and photophysical studies indicate that, in these dinuclear complexes, the protonation state of the bridge may be used to tune the intercomponent interaction between the two metal centers and that these species act as proton driven three-way molecular switches that can be read by electrochemical or luminescence techniques.

A Molecular Plug-Socket Connector

A monocationic plug-socket connector that is composed, at the molecular level, of three components, (1) a secondary dialkylammonium center (CH(2)NH(2)(+)CH(2)), which can play the role of a plug toward dibenzo[24]crown-8 (DB24C8), (2) a rigid and conducting biphenyl spacer, and (3) 1,4-benzo-1,5-naphtho[36]crown-10 (BN36C10), capable of playing the role of a socket toward a 4,4'-bipyridinium dicationic plug, was synthesized and displays the ability to act as a plug-socket connector. The fluorescent signal changes associated with the 1,5-dioxynaphthalene unit of its BN36C10 portion were monitored to investigate the association of this plug-socket connector with the complementary socket and plug compounds. The results indicate that (1) the CH(2)NH(2)(+)CH(2) part of the molecular connector can thread DB24C8 in a trivial manner and (2) the BN36C10 ring of the connector can be threaded by a 1,1'-dioctyl-4,4'-bipyridinium ion only after the CH(2)NH(2)(+)CH(2) site is occupied by a DB24C8 ring. The two connections of the three-component assembly are shown to be controlled reversibly by acid/base and red/ox external inputs, respectively. The results obtained represent a key step for the design and construction of a self-assembling supramolecular system in which the molecular electron source can be connected to the molecular electron drain by a molecular elongation cable.Rogez, G.; Ferrer Ribera, RB.; Credi, A.; Ballardini, R.; Gandolfi, MT.; Balzani, V.; Liu, Y.... (2014). A Molecular Plug-Socket Connector. Journal of the American Chemical Society. 129(15):4633-4642. doi:10.1021/ja067739eS463346421291

Probing inter-ligand excited state interaction in homo and heteroleptic ruthenium(II) polypyridyl complexes using selective deuteriation

The effect of deuteriation on the photophysical properties of two series of regioselectively deuteriated Ru(II) complexes ([Ru(bipy)x(ph2phen)3-x]2+, where x = 0–3 and ph2phen is 4,7-diphenyl-1,10-phenanthroline and [Ru(bipy)2(dcbipy2-)], where H2dcbipy is 4,4'-dicarboxy-2,2'-bipyridyl) is reported. Although overall, deuteriation results in an increase in emission lifetime for all complexes, the effect of substitution of hydrogen for deuterium shows strong regioselectivity both in terms of the ligand and the position on individual ligands that are exchanged.