Synthesis, photophysical and electrochemical characterization of phthalocyanine-based poly(p-phenylenevinylene) oligomers.

The synthesis of two poly(p-phenylenevinylene) oligomers (oPPV) laterally substituted by phthalocyanines (Pc) is described. The preparation of Pc-based oligomers and was accomplished by means of Knoevenagel and Wadsworth-Horner-Emmons reactions, respectively. Diformylphthalocyanine was employed as a monomer in these reactions, thus providing functionalised conjugated oligomers upon reaction with the corresponding co-monomers, and . Photophysical and electrochemical experiments have been carried out with both oligomeric derivatives, revealing excited state interactions such as transduction of singlet excited state energy.

Determination of the attenuation factor in fluorene-based molecular wires.

Fluorene-based bridges exhibit a molecular wire-like behaviour in C(60)-wire-exTTF systems with a very low attenuation factor (beta = 0.09 A(-1)).

Energy transfer in oligofluorene-C60 and C60-oligofluorene-C60 donor-acceptor conjugates.

Two complementary series of C(60)-(Fl)(n) and C(60)-(Fl)(n)-C60 (Fl = 9,9-dihexylfluorene-2,7-diyl; n = 1-5) derivatives with terminal N-methylfulleropyrrolidine units have been synthesized from CHO-(Fl)(n) and CHO-(Fl)(n)-CHO precursors via 1,3-dipolar cycloaddition reaction of in situ generated azomethine ylides with an excess of C60. In solution electrochemical experiments, these conjugates give rise to amphoteric redox behavior. Three consecutive quasireversible reduction waves have been observed at the expected potentials for the N-methylfulleropyrrolidine cores. For the C(60)-(Fl)(n)-C(60) series, each reduction wave is a two-electron process with no observable interaction between the C(60) units. Two or, in some cases, three oxidation waves--most of them irreversible--are ascribed to the oligofluorene system. These waves are cathodically shifted with an increasing number of fluorene units and anodically shifted by the conjugated terminal aldehyde units, compared to the N-methylfulleropyrrolidine termini. Steady-state and time-resolved photolytic techniques show that an efficient transduction of singlet excited-state energy transfer prevails from the photoexcited oligofluorene to the energy accepting fullerene.

Supramolecular bis(rutheniumphthalocyanine)-Perylenediimide ensembles: simple complexation as a powerful tool toward long-lived radical ion pair states.

A novel supramolecular electron donor-acceptor hybrid (1) has been designed through axial coordination of a perylenebisimide moiety [BPyPDI], bearing two 4-pyridyl substituents at the imido positions, to the ruthenium(II) metal centers of two phthalocyanines [Ru(CO)Pc]. This modular protocol enables access to electron donor-acceptor hybrids with potentially great design flexibility. The new array (1) has been characterized by standard spectroscopic methods, and its photophysical behavior has been established by using ultrafast and fast time-resolved techniques. Photoexcitation of either chromophore leads to a product that is essentially identical for both pathways, that is, evolving from the [Ru(CO)Pc] or [BPyPDI] singlet excited state. Features of the photoproduct are new transient maxima at 530 and 725 nm, plus transient minima at 580 nm and 650 nm. Based on the radiolytically generated [BPyPDI*-] (i.e., one-electron reduction of [BPyPDI]) and [Ru(CO)Pc*+] (i.e., one-electron oxidation of [Ru(CO)Pc]) features, which in the 300 and 900 nm range remarkably resemble those noted for photoexcited 1, we attribute the photolytically generated species to the composite spectrum of the [Ru(CO)Pc*+ -BPyPDI*- -RuCOPc] radical ion pair state. Its lifetime, which is on the order of 115 +/- 5 ns, reveals a significant stabilization and confirms that the strongly exothermic charge recombination dynamics are placed deeply in the inverted region of the Marcus parabola.

Liquid-crystalline bisadducts of [60]fullerene.

A second-generation cyanobiphenyl-based dendrimer was used as a liquid-crystalline promoter to synthesize mesomorphic bisadducts of [60]fullerene. Liquid-crystalline trans-2, trans-3, and equatorial bisadducts were obtained by condensation of the liquid-crystalline promoter, which carries a carboxylic acid function, with the corresponding bisaminofullerene derivatives. A monoadduct of fullerene was also prepared for comparative purposes. All the compounds gave rise to smectic A phases. An additional mesophase, which could not be identified, was observed for the trans-2 derivative. The supramolecular organization of the monoadduct derivative is governed by steric constraints. Indeed, for efficient space filling, adequacy between the cross-sectional areas of fullerene (approximately 100 A(2)) and of the mesogenic groups (approximately 22-25 A(2) per mesogenic group) is required. As a consequence, the monoadduct forms a bilayered smectic A phase. The supramolecular organization of the bisadducts is essentially governed by the nature and structure of the mesogenic groups and dendritic core. Therefore, the bisadducts form monolayered smectic A phases. The title compounds are promising supramolecular materials as they combine the self-organizing behavior of liquid crystals with the properties of fullerene.