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Campagna S.,Messina University | Campagna S.,Centro Of Ricerca Interuniversitario Per La Conversione Chimica Dellenergia Solare | Cavazzini M.,CNR Institute of Molecular Science and Technologies | Cusumano M.,Messina University | And 8 more authors.
Inorganic Chemistry | Year: 2011

Efficient intercalation of a luminescent Ir(III) complex exclusively made of polypyridine ligands in natural and synthetic biopolymers is reported for the first time. The emission of the complex is largely enhanced in the presence of [poly(dA-dT) 2] and strongly quenched in the presence of [poly(dG-dC) 2]. By comparing the emission decays in DNA and in synthetic polynucleotides, it is proposed that the emission quenching of the title compound by guanine residues in DNA is no longer effective over a distance of four dA-dT base pairs. © 2011 American Chemical Society.

Boixel J.,University of Nantes | Blart E.,University of Nantes | Pellegrin Y.,University of Nantes | Odobel F.,University of Nantes | And 6 more authors.
Chemistry - A European Journal | Year: 2010

Two families of dyad and triad systems based on perylene monoimide (PMI), quaterthiophene (QT), and 9,10-bis(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (extended tetrathiafulvalene, exTTF) molecular components have been designed and synthesized. The dyads (D1 and D2) are of the PMI-QT type and the triads (T1 and T2) of the PMI-QT-exTTF type. The two families differ in the saturated or unsaturated nature of the linker groups (ethynylene in D1 and T1, ethylene in D2 and T2) that bridge the molecular components. The dyads and triads have been characterized by electrochemical, photophysical, and computational methods. Both the experimental and the computational (DFT) results indicate that in the unsaturated systems strong intercomponent interactions lead to substantial perturbation of the properties of the subunits. In particular, in T1, delocalization is particularly effective between the QT and exTTF units, which would be better viewed combined as a single electronic subsystem. For the dyad systems, the photophysics observed following excitation of the PMI unit is solvent-dependent. In moderately polar solvents (dichloromethane, diethyl ether) fast charge separation is followed by recombination to the ground state. In toluene, slow conversion to the chargeseparated state is followed by intersystem crossing and recombination to yield the triplet state of the PMI unit. The behavior of the triads, on the other hand, is remarkably similar to that of the corresponding dyads, which indicates that, after primary charge separation, hole shift from the oxidized QT component to exTTF is quite inefficient. This unexpected result has been rationalized on the basis of the anomalous (simultaneous two-electron oxidation) electrochemistry of exTTF and with the help of DFT calculations. In fact, although exTTF is electrochemically easier to oxidize than QT by around 0.6 V, the one-electron redox orbitals (HOMOs) of the two units in triad T2 are almost degenerate. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Teresa Indelli M.,University of Ferrara | Teresa Indelli M.,CNR Institute for Organic Syntheses and Photoreactivity | Chiorboli C.,Centro Of Ricerca Interuniversitario Per La Conversione Chimica Dellenergia Solare | Ghirotti M.,University of Ferrara | And 6 more authors.
Journal of Physical Chemistry B | Year: 2010

The photophysical behavior of a series of heterometallic arrays made of a central Sn(IV) porphyrin connected, respectively, to two (SnRu2), four (SnRu4), or six (SnRu6) ruthenium porphyrin units has been studied in dichloromethane. Two different motifs connect the ruthenium porphyrin units to central tin porphyrin core, axial coordination via ditopic bridging ligands and/or coordination to peripheral pyridyl groups of the central porphyrin ring. A remarkable number of electron transfer processes (photoinduced charge separation and recombination processes) have been time-resolved using a combination of emission spectroscopy and fast (nanosecond) and ultrafast (femtosecond) absorption techniques. In these systems both types of molecular components can be selectively populated by light absorption. In all the arrays, the local excited states of these units (the tin porphyrin singlet excited state and the ruthenium porphyrin triplet state) are quenched by electron transfer leading to a charge-separated state where the ruthenium porphyrin unit is oxidized and the tin porphyrin unit is reduced. For each array, the two forward electron transfer processes, as well as the charge recombination process leading back to the ground state, have been kinetically resolved. The rate constants obey standard free-energy correlations with the forward processes lying in the normal free-energy regime and the back reactions in the Marcus inverted region. The comparison between the trimeric (SnRu 2) and pentameric (SnRu4) arrays shows that all the electron transfer processes are faster in the latter than in the former system. This can be rationalized in terms of differences in electronic factors (due to the different connecting motifs) and driving force. In less polar solvents, such as toluene, the energy of the charge-separated states is substantially lifted, leading to a switch (from electron transfer to triplet energy transfer) in the deactivation mechanism of the excited ruthenium triplet. © 2010 American Chemical Society.

Teresa Indelli M.,University of Ferrara | Teresa Indelli M.,Centro Of Ricerca Interuniversitario Per La Conversione Chimica Dellenergia Solare | Chiorboli C.,CNR Institute for Organic Syntheses and Photoreactivity | Scandola F.,University of Ferrara | And 4 more authors.
Journal of Physical Chemistry B | Year: 2010

Two new supramolecular boxes, (ZnMC)2(rPBI)2 and (ZnMC)2(gPBI)2, have been obtained by axial coordination of N/N′-dipyridyl-functionalized perylene bisimide (PBI) dyes to the zinc ion centers of two 2+2 porphyrin metallacycles (ZnMC = [trans,cis,cis-RuCl 2(CO)2(Zn·4′-cis-DPyP)]2). The two molecular boxes involve PBI pillars with different substituents at the bay area: the "red" PBI (rPBI = N,N′-di(4-pyridyl)1,6,7,12-tetra(4- tert-butylphenoxy)perylene-3,4:9,10-tetracaiboxylic acid bisimide) containing tert-butylphenoxy substituents and the "green" PBI (gPBI = N,N′-di(4-pyridyl)-1,7-bis(pyrrolidin-1-yl)perylene-3,4:9, 10tetracarboxylic acid bisimide) bearing pyrrolidinyl substituents. Due to the rigidity of the modules and the simultaneous formation of four pyridine- zinc bonds, these discrete adducts self-assemble quantitatively and are remarkably stable in dichloromethane solution. The photophysical behavior of the new supramolecular boxes has been studied in dichloromethane by emission spectroscopy and ultrafast absorption techniques. A different photophysical behavior is observed for the two systems. In (ZnMC)2(rPBI) 2. efficient electron transfer quenching of both perylene bisimide and zinc porphyrin chromophores is observed, leading to a charge separated state, PBI--Zn+, in which a perylene bisimide unit is reduced and zinc porphyrin is oxidized. In the deactivation of the perylene bisimide localized excited state, an intermediate zwitterionic charge transfer state of type PBI--PBI+ seems to play a relevant role. In (ZnMC)2(gPBI)2. singlet energy transfer from the Zn porphyrin chromophores to the perylene bisimide units occurs with an efficiency of 0.7. This lower than unity value is due to a competing electron transfer quenching, leading to the charge separated state PBI--Zn+. The distinct photophysical behavior of these two supramolecular boxes is interpreted in terms of energy changes occurring upon replacement of the "red" rPBI by "green" gPBI. © 2010 American Chemical Society.

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