[60]Fullerene–porphyrin [n]pseudorotaxanes: self-assembly, photophysics and third-order NLO response

Herein we report a series of porphyrin and methano[60]fullerene that undergo self-assembly.

Synthesis and electronic properties of covalent assemblies of oligophenylenevinylene units arising from a calix

Assemblies of four oligophenylenevinylene moieties arising from a calix[4]arene core, i.e., calix[4]oligophenylenevinylenes, have been prepared by Heck-type cross-coupling reactions of styrene derivatives with a tetraiodinated cone-calix[4]arene precursor. Photophysical studies in solution have revealed that there are electronic ground state interactions between the covalently bonded OPV moieties. The absorption spectra of the calix[4]oligophenylenevinylenes are significantly different from those obtained by summing the spectra of four model units and their emission is red-shifted when compared to the corresponding model compounds. Electrochemical studies have shown that the redox processes of the four OPV subunits do not take place at the same potentials indicating also a strong electronic interaction among them in the calix[4]oligophenylenevinylenes.

Highly luminescent Cu(I)-phenanthroline complexes in rigid matrix and temperature dependence of the photophysical properties

We synthesized new [Cu(NN)(2)](+)-type complexes where NN = 2-5 and denotes a 2,9-disubstituted-1,10-phenanthroline ligand (related complexes of 1 and 6 ligands are used for reference purposes). For 2, 3, and 4 the ligand substituents are long alkyl-type fragments, whereas in 5 a phenyl ring is directly attached to the chelating unit. At 298 K the four complexes display relatively intense metal-to-ligand-charge-transfer (MLCT) emission bands with maxima around 720 nm, Phi(em) approximately 1 x 10(-)(3) and tau > 100 ns in deaerated CH(2)Cl(2). The emission behavior at 77 K in a CH(2)Cl(2)/MeOH matrix is quite different for complexes of alkyl- (2-4) versus phenyl-substituted (5) ligands. The former exhibit very intense emission bands centered around 642 nm and hypsochromically shifted with respect to 298 K, whereas the luminescence band of [Cu(5)(2)](+) is faint and shifted toward the infrared side. These results prompted us to study in detail the temperature dependence of luminescence properties of [Cu(2)(2)](+) and [Cu(5)(2)](+) in the 300-96 K range. For both complexes the excited state lifetimes increase monotonically by decreasing temperatures, and the trend is well described by an Arrhenius-type treatment involving two equilibrated MLCT excited levels. The emission bands show a similar behavior for the two compounds (intensity decrease and red-shift) only in the 300-120 K range, when the solvent is fluid. In the frozen regime (T </= 120 K), the emission intensity of [Cu(5)(2)](+) continues to drop, whereas that of [Cu(2)(2)](+) exhibits a dramatic intensity increase. We interpret this different behavior in terms of structural factors, suggesting that long alkyl-chains in the 2,9-phenanthroline positions are optimal to prevent significant ground- and excited-state distortions in rigid matrix. We show that our results do not contradict current models describing the photophysics of [Cu(NN)(2)](+) but, instead, bring further evidence to support their validity. They also suggest guidelines for the design of Cu(I)-phenanthroline complexes showing optimized luminescence performances both in fluid and in rigid matrix, an elusive goal for over two decades.

Charge-transfer interactions in face-to-face porphyrin-fullerene systems: solvent-dependent luminescence in the infrared spectral region

The cyclophane-type molecular dyads 1 x 2H and 1 x Zn, in which a doubly bridged porphyrin donor adopts a close, tangential orientation relative to the surface of a fullerene acceptor, were prepared by Bingel macrocylization. The porphyrin derivatives 2 x 2H and 2 x Zn with two appended, singly linked C60 moieties were also formed as side products. NMR investigations revealed that the latter compounds strongly prefer conformations with one of the carbon spheres nesting on the porphyrin surface, thereby taking a similar orientation to that of the fullerene moiety in the doubly bridged systems. Cyclic voltammetric measurements showed that the mutual electronic effects exerted by the fullerene on the porphyrin and vice versa are only small in all four dyads, despite the close proximity of the donor and acceptor components. The steady-state and time-resolved absorption and luminescence properties of 1 x Zn and 2 x Zn were investigated in toluene solution and it was shown that, upon light excitation, both the porphyrin- and the fullerene-centered excited states are deactivated to a lower-lying CT state, emitting in the IR spectral region (lambda max = 890 and 800 nm at 298 and 77 K, respectively). In the more polar solvent benzonitrile, this CT state is still detected but, owing to its very low energy (below 1.4 eV), is not luminescent and shorter-lived than in toluene. The remarkable observation of similar photophysical behavior of 1 x Zn and 2 x Zn suggests that a tight donor-acceptor distance cannot only be established in doubly bridged cyclophane-type structures but also in singly bridged dyads, by taking advantage of favourable fullerene-porphyrin ground-state interactions.

A Copper(I) Bis-phenanthroline Complex Buried in Fullerene-Functionalized Dendritic Black Boxes

Virtual inaccessibility to external contact was revealed by electrochemical investigations for a bis(1,10-phenanthroline)copper(I) core embedded in dendrimers with up to 16 peripheral fullerene units (shown schematically). With increasing numbers of fullerene units, less and less light is available to the core, and the small quantity of light energy that reaches the central Cu(I) complex is returned to the external fullerenes by energy transfer-the central core is buried in a dendritic black box.