Abstract: Luminescent metal complexes are key materials for several applications such as lighting, analytical probes, and lasers. In many cases compounds based on precious (i.e. platinum group) and rare earth metals are utilized, which are often rather expensive and environmentally problematic. In recent years, interest is growing in luminescent complexes based on less traditional but more abundant and cheaper metal elements. In this scenario compounds of metals with a d(10) electronic configuration are playing a prominent role, also thanks to the versatility of their luminescent levels which can be of ligand centred, charge transfer or, in the case of polynuclear compounds, even metal-centred nature. Here we focus on some selected examples of Cu(I), Ag(I), Au(I), Zn(II) and Cd(II) luminescent complexes to suggest some possible routes towards promising and unprecedented emitting materials.

Abstract: Heteroleptic copper(I) complexes CuPOP-F and CuFc-F have been prepared from a fullerene-substituted phenanthroline ligand and bis[2-(diphenylphosphino)phenyl] ether (POP) and 1,1'-bis(diphenylphosphino)ferrocene (dppFc), respectively. Electrochemical studies indicate that some ground-state electronic interaction between the fullerene subunit and the metal-complexed moiety are present in both CuPOP-F and CuFc-F. Their photophysical properties have been investigated by steady state and time-resolved UV-vis-NIR luminescence spectroscopy and nanosecond laser flash photolysis in a CH2Cl2 solution and compared to those of the corresponding model copper(I) complexes UPOP and CuFc and of the fullerene model compound F. Selective excitation of the methanofullerene moiety in CuPOP-F results in regular deactivation of the lowest singlet and triplet states, indicating no intercomponent interactions. Conversely, excitation of the copper(I)-complexed unit (405 nm, 40% selectivity)shows that the strongly luminescent triplet metal-to-ligand charge-transfer ((MLCT)-M-3) excited state located at 2.40 eV is quenched by the carbon sphere with a rate constant of 1.6 x 10(8) s(-1). Details on the mechanism of photodynamic processes in CuPOP-F via transient absorption are hampered by the rather unfavorable partition of light excitation between the two chromophores. By determination of the yield of formation of the lowest fullerene triplet level through sensitized singlet oxygen luminescence in the NIR region, it is shown that the final sink of photoinduced processes is always the fullerene triplet. This can be populated via a two-step charge-separation charge-recombination process and a less favored (MLCT)-M-3 -> C-3(60) triplet-triplet energy-transfer pathway. In CuFc-F, both of the photoexcited copper(I)-complexed and fullerene moieties are quenched by the presence of the ferrocene unit, most likely via ultrafast energy transfer.

Abstract: A photophysical, electrochemical and computational study has been performed on a homologous series of cyclometallated Pd(II) (1a-f) and Pt(II) (2a-f) complexes of general formula [(C, N) M(O, O)]; (H(C, N) = azobenzene, 2-phenylpyridine, benzo[ h] quinoline; M = Pd, Pt; H(O, O) = acetylacetone, hexafluoroacetylacetone). Experimental and computational data have shown the strong influence exerted by electronegativity of the ancillary ligand on the frontier orbitals of the complexes, such an effect being enhanced for the Pt(II) species.

Abstract: Two europium complexes {Eu-dbm-carb-phen = tris[1-{[6-(9H-carbazol-9-yl)hexoxy]phenyl}-3-{[6-(9H-carbazol-9-yl)- hexoxy]phenyl}propane- 1,3-dione](1, 10-phenanthroline)-europium(III), Eu.dbm.carb.bath = tris[1-{[6-(9H-carbazol-9-yl)hexoxy]phenyl}-3-{[6-(9H-carbazol-9-yl)hexoxy]phenyl}- propane- 1,3-dione] (bathophenanthroline) europium(III) I and their reference compounds were synthesized and characterized. Each complex contains three different chromophores: carbazole (carb), phenanthroline (phen) (or bathophenanthroline, bath) and dibenzoylmethane (dbm) units. The luminescence properties investigated in dichloromethane solution and in solid matrix show that the carbazole moiety is a better sensitizer for the metal-centred emitting states of the Eu-III ion compared to the dibenzoylmethane and phenanthroline units. Furthermore, the charge-transporting properties of the carbazole moieties appear to be appealing when integrated into the emitting units. Finally, the high number of appended carbazole units confers a strong light-harvesting character to the structure. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

Abstract: A novel dendritic europium complex containing grafted carbazole units as functional peripheries was synthesized and characterized. The Forster energy transfer from the peripheries of carbazole units to beta-diketonate as well as from the ligands to the central Eu(III) ions in the complex was demonstrated. Under the excitation of carbazole units and beta-diketonate, characteristic red emission peaks at 612 run with four shoulders due to the Eu(III) ion transition of D-5(0) -> F-7(j) (J=0-4) were observed for the complex.

Abstract: Highly stable Eu(III) and Tb(III) complexes, emitting in the red and green visible regions, respectively, have been anchored onto a single SiO2 transparent layer, yielding ca. 40 nm thick films; this allows high loading of tailored proportions of the red and green emitters within the films and results in highly uniform and easily colour-tunable luminescent layers.

Abstract: Cu(I) complexes and clusters are the largest class of compounds of relevant photochemical and photophysical interest based on a relatively abundant metal element. Interestingly, Nature has given an essential role to copper compounds in some biological systems, relying on their kinetic lability and versatile coordination environment. Some basic properties of Cu(I) and Cu(II) such as their coordination geometries and electronic levels are compared, pointing out the limited significance of Cu(II) compounds (d(9) configuration) in terms of photophysical properties. Well-established synthetic protocols are available to build up a variety of molecular and supramolecular architectures (e.g. catenanes, rotaxanes, knots, helices, dendrimers, cages, grids, racks, etc.) containing Cu(I)-based centers and exhibiting photo- and electroluminescence as well as light-induced intercomponent processes. By far the largest class of copper complexes investigated to date is that of Cu(I)-bisphenanthrolines ([Cu(NN)(2)](+)) and recent progress in the rationalization of their metal-to-ligand charge-transfer (MLCT) absorption and luminescence properties are critically reviewed, pointing out the criteria by which it is now possible to successfully design highly emissive [Cu(NN)(2)](+) compounds, a rather elusive goal for a long time. To this end the development of spectroscopic techniques such as light-initiated time-resolved X-ray absorption spectroscopy (LITR-XAS) and femtosecond transient absorption have been rather fruitful since they have allowed us to firmly ground the indirect proofs of the molecular rearrangements following light absorption that had accumulated in the past 20 years. A substantial breakthrough towards highly emissive Cu(I) coordination compounds is constituted by heteroleptic Cu(I) complexes containing both N- and P-coordinating ligands ([Cu(NN)(PP)](+)) which may exhibit luminescence quantum yields close to 30% in deaerated CH2Cl2 solution and have been successfully employed as active materials in OLED and LEC optoelectronic devices. Also copper clusters may exhibit luminescence bands of halide-to-metal charge transfer (XMCT) and/or cluster centered (CC) character and they are briefly reviewed along with miscellaneous Cu(I) compounds that recently appeared in the literature, which show luminescence bands ranging from the blue to the red spectral region.

Abstract: A Eu-III complex, tris-dibenzoylmethane mono-1,10-phenanthroline-europium(III) [Eu(DBM)(3)(Phen)], can be easily adsorbed If in situ via hydrophobic interactions to single-walled carbon nanotube (SWNT) surfaces from a methanol solution. The Eu-III containing material has been comprehensively characterized via thermogravimetric analysis (TGA), UV-vis-NIR absorption and luminescence spectroscopy, Raman spectroscopy, atomic force microscopy (AFM), high-resolution transmission electron microscopy (HR-TEM)), Z-contrast scanning transmission electron microscopy (STEM) imaging, and energy dispersive X-ray spectroscopy (EDS). The photophysical investigations revealed that the presence of a SWNT framework does not affect the lanthanide-centered luminescence stemming from the characteristic electronic transitions within the 4f shell of the Eu-III, ions. Such straightforward synthetic route leads to the preparation of luminescent SWNTs without significantly affecting the electronic and structural properties of the carbon framework, opening new possibilities of designing new classes of CNTs for biomedical applications.

Abstract: beta,meso,beta-Fused porphyrin oligomers have many attractive photophysical features such as strong absorption in the near-IR at wavelengths greater than 1000 nm, and high two-photon cross sections. However their ultrafast S-1-S-0 deactivation (k(d) > 10(11) s(-1)) limits potential applications. We have synthesised a deuterated fused porphyrin dimer to test whether deuteration influences the rate of non-radiative deactivation. An efficient synthetic strategy was developed, starting with deuteration of dipyrromethane. Deuteration of the zinc porphyrin dimer does not affect its fluorescence quantum yield in CD2Cl2 (Phi(fD)/Phi(fH) = 1.00 +/- 0.05). This implies that the ultrafast non-radiative deactivation is not simply a consequence of the small S-1-S-0 energy gap. Comparison with other conjugated porphyrin oligomers confirms that the deactivation rate in the edge-fused oligomers is faster than would be expected from the energy gap law. This result indicates that it should be possible to create near-IR dyes with similar S-1-S-0 energy gaps to the beta,meso,beta-fused porphyrin oligomers but with slower rates of S-1-S-0 decay.

Abstract: Three new heteroleptic Cu(I) complexes containing one phenanthroline and one diphosphine type ligand ([Cu(N-N)(P-P)](+)) have been prepared. In particular, one ligand is constituted by 1,10-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2) and 2,9-diphenethyl- 1, 1 0-phenanthroline (3) and the other ligand is in all cases 1, 1'-bis(diphenylphosphino)ferrocene (dppf). Therefore, copper and iron metal centres are quite close one another, as evidenced by X-ray crystal diffraction. The structure together with the electrochemical and photophysical properties of these complexes have been compared to that of the corresponding complexes where dppf has been replaced by bis[2-(diphenylphosphino)-phenyl]ether (POP). Cyclic voltammetric experiments evidenced that the first oxidation process is located on the ferrocene moiety and that oxidation of Cu(I) is moved to more positive potential values and a chemical reaction is coupled to the electron transfer process. The absorption spectra show a metal-to-ligand charge transfer (MLCT) band, typical of Cu(I) phenanthroline complexes, at a higher energy compared to the homoleptic [Cu(N-N)(2)](+) species. No emission at either room temperature or 77 K has been observed for compounds 2 and 3, contrary to the high luminescence observed for the corresponding POP complexes. This result is consistent with a photoinduced energy transfer from the Cu(I) complex to the ferrocene moiety. (c) 2006 Elsevier B.V. All rights reserved.

Abstract: A dinuclear Eu(M) complex Eu-2(DBM)(6)TPPD (Hexa(dibenzoyl-methanido)-(N, N, N, N-tetra (2-pyridyl) 1, 4-phenylenediamine)-dieuropium(III)) was synthesized by employing DBM (dibenzoylmethane) and TPPD (N, N, N, N-Tetra(2-pyridyl)-1, 4-phenyl-enediamine) as sensitizing ligands for the Ell( III) ion and a bridging ligand, respectively. The analysis of the absorption, excitation, and emission spectra of the dinuclear complex along with a comparison with analogous mononuclear complex containing the same (beta-diketone ligands and 1, 10-phenanthroline (phen) suggests that the dinuclear complex follows the luminescence mechanism of general Ln(III) complexes.

Abstract: Homo- and heteroleptic copper(I) complexes obtained from various chelating bis-phosphine ligands and Cu(CH3CN)(4)BF4 have been used for the preparation of light emitting devices.

Abstract: The two-component ligand systems 1 and 2 which contain 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) as the hosting unit for the lanthanide cations, and naphthalene (which is devoid of any chelating ability) or quinoline units, respectively, as chromophores, were synthesized. The 1:1 complexes with Gd3+, EU3+ and Tb3+ have been studied in aqueous solution. Relaxometric properties for Gd center dot 1 indicate that two water molecules (q = 2) are in the first coordination sphere of the metal ion whereas for Gd center dot 2, q < 2 is found. For Gd center dot 1, these results indicate that the naphthalene unit is not coordinated to the metal centre; for the case of quinoline, reasons for the lower hydration state are discussed. In case of Eu center dot 1, Tb center dot 1, Eu center dot 2, and Tb center dot 2 the absorption and luminescence spectra, the overall luminescence efficiencies, and the metal-centred lifetimes, were obtained both in water and deuterated water. The coordination features of these complexes were explored by comparing their luminescence properties, resulting in hydration state q = 2 and 1.4 for the cases of the complexes of I and 2, respectively. Use of the photophysical parameters in air-equilibrated water allowed the determination of the ligand-to-cation energy transfer efficiency, Phi(EnT), leading to the overall emission sensitization process. For Eu center dot 1, and Eu center dot 2, we found Phi T-En = 0.034 and 0.078, respectively, supporting that also a non-coordinating chromophore like naphthalene, case of ligand 1, can transfer excitation energy to the metal centre. (C) 2007 Elsevier B.V. All rights reserved.

Abstract:

Abstract: Oligophenylenevinylene (OPV) -terminated phenylenevinylene dendrons G1-G4 with one, two, four, and eight "side-arms", respectively, were prepared and attached to C-60 by a 1,3-dipolar cycloaddition of azomethine ylides generated in situ from dendritic aldehydes and N-methylglycine. The relative electronic absorption of the OPV moiety increases progressively along the fullerodendrimer family C(60)G1-C(60)G4, reaching a 99:1 ratio for C(60)G4 (antenna effect). UV/Vis and near-IR luminescence and transient absorption spectroscopy was used to elucidate photoinduced energy and electron transfer in C(60)G1-C(60)G4 as a function of OPV moiety size and solvent polarity (toluene, dichloromethane, benzonitrile), taking into account the fact that the free-energy change for electron transfer is the same along the series owing to the invariability of the donor-acceptor couple. Regardless of solvent, all the fullerodendrimers exhibit ultrafast OPV --> C-60 singlet energy transfer. In CH2Cl2, the OPV-->C-60 electron transfer from the lowest fullerene singlet level (C-1(60)*) is slightly exergonic (Delta G(CS) approximate to 0.07 eV), but is observed, to an increasing extent, only in the largest systems C(60)G2-C(60)G4 with lower activation barriers for electron transfer. This effect has been related to a decrease of the reorganization energy upon enlargement of the molecular architecture. Structural factors are also at the origin of an unprecedented OPV --> C-60 electron transfer observed for C(60)G3 and C(60)G4 in apolar toluene, whereas in benzonitrile, electron transfer occurs in all cases. Monitoring of the lowest fullerene triplet state by sensitized singlet oxygen luminescence and transient absorption spectroscopy shows that this level is populated through intersystem crossing and is not involved in photoinduced electron transfer.

Abstract: A calix[4] arene scaffolding has been used to construct bisporphyrin ("jaws" porphyrin) hosts for supramolecular binding of fullerene guests. Fullerene affinities were optimized by varying the nature of the covalent linkage of the porphyrins to the calixarenes. Binding constants for C-60 and C-70 in toluene were explored as a function of substituents at the periphery of the porphyrin, and 3,5-di-tert-butylphenyl groups gave rise to the highest fullerene affinities ( 26 000 M-1 for C-60). The origin of this high fullerene affinity has been traced to differential solvation effects rather than to electronic effects. Studies of binding constants as a function of solvent (toluene < benzonitrile < dichloromethane, cyclohexane) correlate inversely with fullerene solubility, indicating that desolvation of the fullerene is a major factor determining the magnitude of binding constants. The energetics of fullerene binding have been determined in terms of Delta H and Delta S and are consistent with an enthalpy-driven, solvation-dependent process. A direct relationship between supramolecular binding of a fullerene guest to a bisporphyrin host and the appearance of a broad NIR absorption band have been established. The energy of this band moves in a predictable manner as a function of the electronic structure of the porphyrin, thereby establishing its origin in porphyrin-to-fullerene charge transfer.

Abstract: The electron and energy accepting properties of fullerene C-60 can be readily exploited upon the selection of suitable donating species to construct supramolecular assemblies which display photoinduced electron and/or energy transfer processes. In this account we focus on the use of transition metal complexes in the role of the electron/energy donor, in particular we discuss the photophysical properties of some fullerene hybrid systems containing tris(2,2'-bipyridine)ruthenium(II), (2,2'-bipyridine)rhenium (1) or bis(1,10-phenanthrolinc)copper(l) subunits that we have investigated over the years. In fullerene hybrid dyads with Ru(II) and Re(l) complexed moieties, electron transfer is observed at room temperature in both cases, while it is blocked at 77 K in the former case. For multicomponent arrays (rotaxane, dendrimers, helicates) with Cu(l)-bisphenanthroline moieties, quenching by electron/energy transfer of the MLCT excited states of the metal complexed moiety is always found. When excitation is addressed to the carbon cage, photoinduced processes occurs when methanofullerenes are involved, but not with bismethanofullerenes.

Abstract: The new, sterically encumbered phenanthroline ligands 1a,b, both characterized by the presence of bulky aryl substituents (3,5-di-tert-butyl-4-methoxyphenyl, 2,4,6-trimethylphenyl) in the 2,9-position, were prepared along with their homoleptic [Cu(1a,b)(2)](+) and heteroleptic complexes [Cu(1a,b)(phen)](+) (phen = parent 1,10-phenanthroline). Due to the pronounced steric shielding, particularly effective in ligand la, the formation of the homoleptic complex [Cu(1a)2]+ becomes very slow (5 days). Once formed, the homoleptic complexes [Cu(1a,b)2]+ do not exchange ligands even with phen added in excess because they are kinetically locked due to the large tert-butylphenyl substituents at the phenanthroline unit. The electronic absorption spectra of the homoleptic complexes [Cu(1a)(2)](+) and [Cu(1b)(2)](+) evidence a strongly different ground state geometry of the two compounds, the former being substantially more distorted. This trend is also observed in the excited-state geometry, as derived by emission spectra and lifetimes in CH2Cl2 solution. The less distorted [Cu(1b)(2)](+), compared to [Cu(1a)(2)](+), is characterized by a 15- and over 100-fold stronger emission at 298 and 77 K, respectively. Noticeably, the excited-state lifetime of [Cu(1a)(2)](+) in solution is unaffected by the presence of molecular oxygen and only slightly shortened in nucleophilic solvents. This unusual behavior supports the idea of a complex characterized by a "locked" coordination environment.

Abstract: The preparation of sol-gel glasses is described wherein highly stable Eu(III) centres are anchored to the silica glass upon acidic hydrolysis and by using tetraethylorthosilicate (TEOS) as a silica source. The complex employed is Eu center dot 1 and is obtained from bipartite ligand 1, which features a DO3A macrocycle as a hosting unit for the Eu(III) centre, a methoxy-acetophenone unit as an antenna chromophore, and an alkyl chain bearing one primary hydroxy group (DO3A is 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid). Eu? 1 is linked to the forming silica glass through the -OH groups and a uniform distribution of the luminescent centres is obtained, as indicated by results from secondary ion mass spectrometry in-depth profiling. The luminescent efficiency of the Eu(III) centres in the solid matrix is evaluated to be 10%, which is comparable to that of Eu center dot 1 in water solution and of a convenient reference complex, Eu center dot 2 (2 is a ligand featuring the same hosting and antenna functionalities of 1, wherein the -OH residue is replaced by an unreactive group, a benzoylmethyl residue). A discussion is given of the photophysical properties exhibited by the complexes in the film and in solution.

Abstract: Symmetrically substituted oligophenylenevinylene (OPV) derivatives bearing terminal p-nitrophenylhydrazone groups have been prepared and used for the synthesis of dumbbell-shaped bis(pyrazolino[60]fullerene)OPV systems. In these triad arrays, the OPV-type fluorescence is dramatically quenched as a consequence of ultrafast OPV -> C-60 singlet energy transfer. In its turn the fullerene singlet state is quenched by pyrazoline -> C-60 electron transfer, in line with the behavior of the corresponding reference fullerene molecule. The occurrence of electron transfer in the multicomponent arrays is evidenced by recovery of fullerene fluorescence at 77 K in CH2Cl2, and in toluene at 298 K. Under these conditions the OPV -> C-60 energy transfer is unaffected. The rate of this process turns out to be higher for the OPV trimer than for the corresponding pentameric OPV arrays, in agreement with energy-transfer theory expectations. Scanning tunneling microscopy (STM) and scanning force microscopy (SFM) revealed that the bis(pyrazolino[60]fullerene)-OPV can self-assemble into ordered layered crystalline architectures on the basal plane of highly oriented pyrolitic graphite.

Abstract: The Nile Red dye, H(NR), forms cyclometalated R-2-disubstituted-acetylacetonato square planar Pd(II) complexes (1-3; R = CH3, CF3, C6H5 respectively) whose photophysical properties were tested in cyclohexane, dichloromethane or methanol solutions. In cyclohexane 1-3 emit in the range 580-650 nm with a quantum yield ranging from 0.12 (R = CH3) to 0.50 (R = CF3) and lifetimes between 0.88 and 4.46 ns. These complexes form a new family of notably efficient red emitting organometallic dyes which Could be of interest for practical applications. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: The synthesis of a new ligand (1) containing a single phenanthroline (phen) chromophore and a flexibly connected diethylenetriamine tetracarboxylic acid unit (DTTA) as a anthanide (Ln) coordination site is reported [1 is 4-[(9methyl-1,10-phenantrol-2-yl)methyl]-1,4,7-triazaheptane-1,1,7,7-tetraacetic acid]. From 1, an extended series of watersoluble Ln.1 complexes was obtained, where Ln is Eu(III), Tb(III), Gd(III), Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), and Er(III). The stoichiometry for the association was found 1:1, with an association constant K-A greater than or equal to 10(7)s(-1) as determined by employing luminescence spectroscopy. The luminescence and photophysical properties of the series of lanthanide complexes were investigated in both H2O and D2O solutions. High efficiencies for the sensitized emission, os, in air-equilibrated water were observed for the Ln.1 complexes of Eu(Ill) and Tb(Ill) in the visible region (phi(se) = 0.24 and 0.15, respectively) and of Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Ncl(III), and Er(III) in the vis and/or near-infrared region [phi(se) = 2.5 x 10(-3), 5 X 10(-4), 3 x 10(-5), 2 x 10(-5), 2 x 10(-4), 4 x 10(-5), and (in D2O) 4 x 10(-5), respectively]. For Eu.1 and Tb.1, luminescence data for water and deuterated water allowed us to estimate that no solvent molecules (q) are bound to the ion centers (q = 0). Luminescence quenching by oxygen was investigated in selected cases.

Abstract: Mononuclear complexes [Re(bpym)(CO)(3)Cl] and [Pt(bpym)(CC-C6H4CF3)(2)] (bpym = 2,2'-bipyrimidine), in which one of the bipyrimidine sites is vacant, have been used as "complex ligands" to prepare heterodinuclear d-f complexes in which a lanthanide tris(1,3-diketonate) unit is attached to the secondary bipyrimidine site to evaluate the ability of d-block chromophores to act as antennae for causing sensitized near-infrared (NIR) luminescence from adjacent lanthanide(III) centers. The two sets of complexes so prepared are [Re(CO)(3)Cl(mu-bpym)Ln(fod)(3)] (abbreviated as Re-Ln; where Ln = Yb, Nd, Er) and [(F3C-C6H4-CC)(2)Pt(mu-bpym)Ln(hfac)(3)] (abbreviated as Pt-Ln; where Ln = Nd, Gd). Members of both series have been structurally characterized; the metal-metal separation across the bipyrimidine bridge is approximate to6.3 Angstrom in each case. In these complexes, the (MLCT)-M-3 (MLCT = metal to ligand charge-transfer) luminescences of the mononuclear [Re(bpym)(CO)(3)Cl] and [Pt(bpym)(CC-C6H4CF3)(2)] complexes are quenched by energy transfer to those lanthanides (Ln = Yb, Nd, Er) that have low-lying f-f states capable of NIR luminescence; as a result, sensitized NIR luminescence is seen from the lanthanide center following excitation of the d-block unit. In the solid state, quenching of the luminescence from the cl-block chromophore is complete, indicating efficient d --> f energy transfer, as a result of the short metal-metal separation across the bipyrimidine bridge. In a CH2CI2 solution, partial dissociation of the dinuclear complexes into the mononuclear units occurs, with the result that some (MLCT)-M-3 luminescence is observed from mononuclear [Re(bpym)(CO)(3)Cl] or [Pt(bpym)(CC-C6H4CF3)(2)] present in the equilibrium mixture. Solution UV-vis and luminescence titrations, carried out by the addition of portions of Ln(fod)(3)(H2O)(2) or Ln(hfaC)(3)(H2O)(2) to the d-block complex ligands, indicate that binding of the lanthanide tris(1,3-diketonate) unit at the secondary bipyrimidine site to give the d-f dinuclear complexes occurs with an association constant of ca. 10(5) M-1.

Abstract: We report the synthesis and physical properties of novel fullerene-oligoporphyrin dyads. In these systems, the C-spheres are singly linked to the terminal tetrapyrrolic macrocycles of rod-like meso,meso-linked or triply-linked oligoporphyrin arrays. Monofullerene-mono(Zn-II porphyrin) conjugate 3 was synthesized to establish a general protocol for the preparation of the target molecules (Scheme 1). The synthesis of the meso,meso-linked oligopophyrin-bisfullerene conjugates 4-6, extending in size up to 4.1 nm (6), was accomplished by functionalization (iodination followed by Suzuki cross-coupling) of the two free meso-positions in oligomers 21-23 (Schemes 2 and 3). The attractive interactions between a fullerene and a Zn-II porphyrin chromophore in these dyads was quantified as Delta G = -3.3 kcal mol(-1) by variable-temperature (VT) H-1-NMR spectroscopy (Table 1). As a result of this interaction, the C-spheres adopt a close tangential orientation relative to the plane of the adjacent porphyrin nucleus, as was unambiguously established by H-1- and C-13-NMR (Figs. 9 and 70), and UV/VIS spectroscopy (Figs. 13-15). The synthesis of triply-linked diporphyrin-bis[60]fullerene conjugate 8 was accomplished by Bingel cyclopropanation of bis-malonate 45 with two C-60 Molecules (Scheme 5). Contrary to the meso,meso-linked systems 4-6, only a weak chromophoric interaction was observed for 8 by UV/VIS spectroscopy (Fig. 16 and Table 2), and the H-1-NMR spectra did not provide any evidence for distinct orientational preferences of the C-spheres. Comprehensive steady-state and time-resolved UV/VIS absorption and emission studies demonstrated that the photophysical properties of 8 differ completely from those of 4-6 and the many other known porphyrin-fullerene dyads: photoexcitation of the methano[60]fullerene moieties results in quantitative sensitization of the lowest singlet level of the porphyrin tape, which is low-lying and very short lived. The meso,meso-linked oligoporphyrins exhibit O-1(2) sensitization capability, whereas the triply-fused systems are unable to sensitize the formation Of O-1(2) because of the low energy content of their lowest excited states (Fig. 18). Electrochemical investigations (Table 3, and Figs. 19 and 20) revealed that all oligoporphyrin arrays, with or without appended methano[60]fullerene moieties, have an exceptional multicharge storage capacity due to the large number of electrons that can be reversibly exchanged. Some of the Zn-II porphyrins prepared in this study form infinite, one-dimensional supramolecular networks in the solid state, in which the macrocycles interact with each other either through H-bonding or metal ion coordination (Figs. 6 and 7).

Abstract: We report on the photophysical, morphological and photoresponse properties of blends of a regioregular poly(3-hexylthiophene) (P3HT) as the electron-donor and a quinquethiophene-S,S-dioxide (T5OHM) as the electron-acceptor. A scanning force microscopy study on 100 nm thick blended films revealed the occurrence of a notable phase segregation between the two components and a remarkable tendency of the acceptor molecule to form micrometre sized architectures characterized by sharp edges within the amorphous matrix of P3HT. X-Ray diffraction studies confirmed the high degree of crystallinity of T5OHM in the blended films. The interaction of the oligomer with the polymer resulted in an enhanced photoinduced charge separation, leading to a sixty-fold increase of the power conversion efficiency in the blended cells with respect to the pristine device based on neat P3HT.

Abstract: The electrochemical and photophysical properties of molecular architectures consisting of oligomeric meso,meso-linked oligoporphyrin rods linked at both extremities to methanofullerene moieties are presented in comparison to those of model systems, Cyclic voltammetry data evidence the presence of a strong intramolecular electronic coupling along the porphyrin oligomers that varies slightly with their length. This interaction affects the redox potentials of both fullerene and porphyrin moieties. The electronic coupling between the two chromophores is confirmed by comparing the redox potentials of porphyrin arrays before and after attachment of the carbon sphere. Electronic absorption, fluorescence, and phosphorescence spectra of the porphyrin oligomers in toluene are reported, which provide the energy of the lowest singlet and triplet electronic excited states. In the fullerene-porphyrin conjugates, ground-stote charge-transfer (CT) interactions are evidenced by low-energy absorption features above 750 nm. These systems also exhibit near-infrared (NIR) CT luminescence in toluene with lifetimes shorter than 1000 ps. On increasing the solvent polarity (from toluene to Et2O and THF), CT emissions become progressively weaker, red-shifted, and shorter lived, which reflects the energy-gap low and Marcus inverted region effects. Luminescence is not detected in benzonitrile. Picosecond transient absorption spectroscopy of the porphyrin-fullerene conjugates allows detection of the porphyrin cation as a clear fingerprint for electron transfer. The rate of charge recombination is in agreement with CT luminescence lifetimes, which confirms the occurrence of NIR radiative back-electron transfer.

Abstract: Heck and Sonogashira cross-coupling reactions have been used for the functionalization of the upper rim of a tetraiodinated calix[4] arene. In this way, oligophenylenevinylene (OPV) and oligophenyleneethynylene (OPE) arrays have been constructed on the calix[4] arene core to produce covalent assemblies of four pi-conjugated chromophores. Electrochemical properties have been investigated by cyclic voltammetry in different solvent/electrolyte systems. Both OPV and OPE calixarenes show the simultaneous reduction of three out of four units, followed, at more negative potential, by the reduction of the fourth unit. This behaviour can be rationalized in view of a partial deconjugation in one OPV or OPE unit. On the other hand, these calixarenes show only oxidation processes corresponding to the exchange of one electron, thus demonstrating the lack of electrochemical equivalency of the OPV or OPE units, in contrast to the reduction behaviour. Electronic absorption and emission spectra have been recorded in solvents of different polarity ( toluene, dichloromethane, and benzonitrile). The absorption spectra of the OPV calixarene do not match to the sum of the component units as a consequence of the partial deconjugation of the OPV arms in the calixarene structure. On the contrary, fluorescence spectra, quantum yields and excited state lifetimes of the OPV calixarene are nearly identical to those of the corresponding model compound. The trend of the absorption and emission spectra for the OPE calixarene is reversed relative to that of the OPV counterpart. Absorption spectra are well-matched with those of four trimeric OPE fragments but emission spectra exhibit, besides the typical OPE monomeric fluorescence, a broader and longer-lived emission feature on the low-energy spectral side, attributable to excimer-type interactions. Therefore the arrangement of OPV or OPE units within the same calix-4-arene skeleton brings about different effects on the electronic and luminescence properties of the multicomponent system.

Abstract: Highly soluble dendritic branches with fullerene subunits at the periphery and a carboxylic acid function at the focal point have been prepared by a convergent approach. They have been attached to an oligophenylenevinylene (OPV) core bearing two alcohol functions to yield dendrimers with two, four or eight peripheral C,, groups. Their photophysical properties have been systematically investigated in solvents of increasing polarity; that is, toluene, dichloromethane, and benzonitrile. Ultrafast OPV --> C-60 singlet energy transfer takes place for the whole series of dendrimers, whatever the solvent. Electron transfer from the fullerene singlet is thermodynamically allowed in CH,Cl, and benzonitrile, but not in apolar toluene. For a given solvent, the extent of electron transfer, signaled by the quenching of the fullerene fluorescence, is not the same along the series, despite the fact that identical electron transfer partners are present. By increasing the dendrimer size, electron transfer is progressively more difficult due to isolation of the central OPV core by the dendritic branches, which hampers solvent induced stabilization of charge separated couples. Compact structures of the hydrophobic dendrimers are favored in solvents of higher polarity. These structural effects are also able to rationalize the unexpected trends in singlet oxygen sensitization yields.

Abstract: We have utilized oligophenylenevinylenes (OPV) as building blocks in multicomponent arrays featuring controlled photoinduced processes. We describe here three different systems. An OPV-fulleropyrazoline array exhibiting both an energy and an electron transfer terminal for the carbon sphere. The OPV moiety acts as an antenna unit. Then we present a dyad combining an OPV group with a protonable phenanthroline unit, in which the direction of photoinduced energy transfer can be tuned by proton input, enabling the ON/OFF switching of the luminescence of the OPV moiety. Finally a Cu(I)-bisphenanthroline complex with an appended OPV trimer or tetramer unit is described. The OPV luminescence is quenched by the nearby metal complex while, in its turn, the OPV unit imposes structural constraint to the metal center, affecting the metal-to-ligand-charge-transfer luminescence properties in rigid matrix. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: Here we report our recent progresses in the synthesis and the study of fullerene-containing macromolecules. For example, poly(aryl ether) dendritic branches terminated with peripheral triethyleneglycol chains have been attached to C-60. Their photophysical properties have been systematically investigated in three solvents, namely toluene, dichloromethane, and acetonitrile. The changes observed in the photophysical properties along the series suggest an increasing interaction between the poly(aryl ether) dendritic wedges and the fullerene core, which brings about an increasing isolation of the central chromophore towards the exterior. Finally, thanks to their high solubility, these fullerodendrimers have been easily incorporated in mesoporous silica glasses and measurements on the resulting doped samples have revealed efficient optical limiting properties. Fullerene-containing polyesters have also been prepared by polycondensation of a bifunctional fullerene adduct with tetraethyleneglycol. These polymers have been obtained in good yields and found to have quite high molecular weights. Thanks to their good solubility in common organic solvents and to their good film-forming properties, these fullerene-containing polyesters are easy to process and could be used to evaluate their potential for the preparation of all-polymer donor/acceptor bulk heterojunction photovoltaic cells. (C) 2003 Published by Elsevier Ltd.

Abstract: We describe the syntheses, the H-1 NMR studies in CD3OD and D2O as solvent, the X-ray characterization, and the luminescence properties in D2O solution of the two complexes Eu.1 and Er.1, where 1 is a dipartite ligand that includes (i) a 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) unit serving as hosting site for the metal center; and (ii) a phenanthroline unit which plays the role of light antenna for the sensitization process of the metal centered luminescence. In a previous report (Inorg. Chem. 2002, 41, 2777), we have shown that for Eu.1 there are no water molecules within the first coordination sphere. X-ray and H-1 NMR results reported here are consistent with full saturation of the nine coordination sites within the Eu.1 and Er.1 complexes. In addition, these studies provide important details regarding the conformations, square antiprism (SAP) and twisted square antiprism (TSAP), adopted in solution by these complexes. The luminescence results are consistent with both an effective intersystem crossing (ISC) at the light absorbing phenanthroline unit (lambda(exc) = 278 nm) and an effective energy transfer (en) process from the phenanthroline donor to the cation acceptor (with unit or close to unit efficiency for both steps). In D2O solvent, the overall sensitization efficiency, phi(se), is 0.3 and 5 x 10(-6), for Eu.1 (main luminescence peaks at 585, 612, 699 nm) and Er-1 (luminescence peak at 1530 nm), respectively. The photophysical properties of both complexes are discussed with reference to their structural features as elucidated by the obtained H-1 NMR and X-ray results.

Abstract: Transient absorption spectrometry of Cu(I)-phenanthrolines in CH2Cl2 reveals ligand-independent dynamic processes lasting 15 ps, which are associated with the peculiar structural rearrangements occurring for this class of compounds upon photoexcitation.

Abstract:

Abstract: Copper(I) complexes obtained from 2,9-diphenyl-1,10-phenanthroline derivatives substituted with an oligophenylenevinylene (OPV) unit have been prepared. Very strong intramolecular quenching of the lowest OPV excited state by the copper(I) complex has been evidenced in these multicomponent systems. The mechanism of the photoinduced process depends on the length of the conjugated OPV backbone. Upon irradiation of the OPV unit, quantitative sensitization of the Cu(I) complex has been evidenced for the system substituted with trimeric OPV units, but not for those with tetrameric OPV units. Therefore, energy transfer is the sole quenching mechanism for the former complex, whereas electron transfer might play a role in the latter case. This different behaviour is ascribed to the slightly increased electron-accepting character of the OPV tetrameric unit when compared to the corresponding trimer. As far as excited state deactivation in the copper(I) complex is concerned, the hybrid compounds exhibit the characteristic luminescence band attributable to the deactivation of low-lying metal-to-ligand charge transfer (MLCT) excited state(s). As shown by the comparison with a model copper(I) complex, the OPV units have no influence on the MLCT excited state(s) deactivation at room temperature in fluid solutions. In contrast, they are capable of acting as "hooks'' when the measurements are performed at low temperature in a rigid matrix, thus reducing the excited state distortion of the copper(I) complex. As a result, at 77 K the MLCT emission spectral shapes and band maxima of the hybrid compounds are no longer identical to those of the corresponding model complex.

Abstract: Owing to their special photophysical properties, fullerene derivatives are good candidates to demonstrate dendritic effects. In particular, the triplet lifetimes of a C-60 core can be used to evaluate its degree of isolation from external contacts. On the other hand, the fullerene core can act as a terminal energy receptor in dendrimer-based light-harvesting systems. When a fullerodendrimer is further functionalized with a suitable electron donor, it may exhibit the essential features of a multicomponent artificial photosynthetic system in which photoinduced energy transfer from the antenna to the C-60 core is followed by electron transfer.

Abstract: Two ruthenium complexes [Ru(phen)(2)(m-36)](2+) and [Ru(aphen)2(m-36) 121, indicated as 1 and 2 respectively, which contain a 36-membered macrocycle incorporating a sterically hindered bipyridine (m-36), and two 1,10-phenanthroline (phen) or 4-(P-anisyl)-1,10-phenanthroline (aphen) ligands, have been synthesised. Under light irradiation, as seen from the metal-to-ligand-charge-transfer (MLCT) bands of the visible spectral region, the [Ru(phen)12 2+ core of I and 2 is selectively expelled from the macrocycle to give the corresponding bis-acetonitrile derivative. This photochemical process was found to be notably less efficient than that observed in a simpler related complex [Ru(phen)(2)dmbp](2+) (dmbp = 6,6'dimethyl-2,2'-bipyridine), that lacks the macrocyclic motif. In the case of I thermal back reaction takes place quantitatively affording a completely reversible system. The isolation, by chromatographic techniques, of the axial-axial cis-[(a,a)Ru(dphen)(2)Cl-2] isomer, where the two aphen ligands bear two p-anisyl groups disposed trans to one another enabled the preparation of 2. This type of complex undergoes a more complicated photochemical process, in fact, following the expected photolabilisation of the [Ru(aphen)(2)](2+) unit, photoisomerisation of the primary photo-product occurs and gives a statistical mixture of the three geometrical isomers: cis-[(a, a)Ru(aphen)(2)(CH3CN)(2)] (PF6)(2), cis-[ (a, e)Ru(aphen)(2)(CH3CN)(2)](PF6)(2) and cis-[ (e,e)Ru(aphen)(2)(CH3CN)(2)](PF6)(2) This side-reaction precludes its use as rotaxane precursor suggesting that, for this purpose, a bis-phenanthroline ligand stabilising the ruthenium core is needed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

Abstract: In a dinuclear complex containing {Ru(bpy)(3)}(2+) and {Os(bpy)(3)}(2+) termini separated by a flexible diaza-18-crown-6 macrocyclic spacer, binding of a Ba2+ ion at the central macrocycle results in an increase in the Ru...Os separation for electrostatic reasons, and hence a decrease in the efficiency of Ru --> Os photoinduced energy-transfer. (C) 2003 Elsevier Science B.V. All rights reserved.

Abstract: A series of potentially dinucleating ligands, each with two bidentate imino-pyridine compartments, has been used to prepare the mononuclear complexes [Re(CO)(3)Cl(L")] (n = 1-4) which each have a vacant binding site and so constitute 'complex ligands' for the stepwise synthesis of heterodinuclear complexes. Three of the complexes (with L-1, L-2 and L-4) have been structurally characterised. The mononuclear complex [Re(CO)(3)Cl(L-5)], arising from decomposition of [Re(CO)(3)Cl(L-3)] by hydrolysis of the non-coordinated imine unit, was also isolated and structurally characterised. Luminescence studies show that these compounds are only very weak emitters. The 'complex ligand' [Re(CO)(3)Cl(L-1)] has been reacted with [Ln(hfac)(3)] . 2H(2)O (Ln = Yb, Er) to prepare the heterodinuclear complexes [Re(CO)(3)Cl(mu-L-1)Ln(hfac)(3)] in which the {Ln(hfac)}(3) unit is attached to the second bidentate imino-pyridine site of [Re(CO)(3)Cl(L-1)]. The crystal structures of these show that the bridging ligand has to twist to accommodate the two bulky metal fragments. and that the lanthanide units have an 8-coordinate square-antiprismatic geometry. (C) 2003 Elsevier B.V. All rights reserved.

Abstract: A new fullerene-substituted phenanthroline ligand has been obtained by reaction of a phenanthroline derivative bearing a 1,3-phenylenebis(methylene)-tethered bis-malonate with C-60 in a double Bingel cyclopropanation. The relative position of the two cyclopropane rings in the resulting bis-methanofullerene derivatives has been determined on the basis of the molecular symmetry (C,) deduced from the H-1 and C-13 NMR spectra. The corresponding Cu(I) complex F-Cu-F has been prepared in good yields by treatment of the ligand with Cu(CH3CN)(4)BF4. In the resulting multicomponent system, both C60 moieties are in a tangential orientation relative to their bridging phenyl ring, and the central bis(phenanthroline)Cu(I) core is sandwiched between the two carbon spheres. The electrochemical properties of F-Cu-F suggest the existence of ground-state electronic interactions in this multicomponent array based on the mutual effects exerted by the fullerene units to the bis(2,9-diphenyl-1,10-phenanthroline)Cu(I) complex and vice versa. Close vicinity and electronic interactions between the inorganic core and the peripheral fullerene units are also suggested by increased electronic absorption around 430 nm. The distance between the two moieties is estimated to be 4.3 Angstrom by molecular modeling studies. The excited-state properties of F-Cu-F have also been investigated. Photoinduced electron transfer from the central chromophore to the external fullerene units occurs but, surprisingly, only following population of the excited states of the central inorganic unit and not of the external carbon spheres. This is mainly attributed to kinetic factors related to the different nature of the two types of excited states involved, namely charge transfer (excitation on the metal-complexed moiety) vs a localized state (excitation on the fullerene units).

Abstract: Dendrimers with a C-60 core have been obtained by cyclization of dendritic bis-malonate derivatives at the carbon sphere. The resulting bis-methanofullerene derivatives have been characterised by electrospray (ES) and/or MALDI-TOF mass spectrometries. UV-VIS absorption spectra, fluorescence spectra, and fullerene singlet excited state lifetimes have been determined in solvents of different polarity (toluene. dichloromethane, acetonitrile). These data suggest a tighter core/periphery contact upon increase of solvent polarity and dendrimer size. In all the investigated solvents, the fullerene triplet lifetimes are steadily increased with the dendrimer volume, reflecting lower diffusion rates of O-2 inside the dendrimers along the series. Measurements of quantum yields of singlet oxygen sensitization indicate that longer lived triplet states generate lower amounts of singlet oxygen (O-1*(2)) in dichloromethane but not in apolar toluene suggesting a tighter contact between the dendritic branches and the fullerene core in CH2Cl2. In acetonitrile, the trend in singlet oxygen production is peculiar. Effectively, enhanced singlet oxygen production is monitored for the largest dendrimer. This reflects specific interactions of excited O-1*(2) molecules with the dendritic wedges, as probed by singlet oxygen lifetime measurements, possibly as a consequence of trapping effects. (C) 2003 Elsevier Science Ltd. All rights reserved.

Abstract: Fullerene derivatives A-3PV and B-3PV in which an oligophenylenevinylene trimeric subunit (3PV) is attached to C-60 through, respectively, a pyrrolidine or a pyrazoline ring have been prepared. The electrochemical and excited-state properties Of the multicomponent arrays A-3PV and B-3PV have been investigated in Solution using the related oligophenylenevinylene derivative 3PV, fullerenopyrrolidine A and fullerenopyrazoline B as reference Compounds. In A-3PV quantitative OPV --> C-60 photoinduced singlet-singlet energy transfer has been observed. Population of the lowest fullerene singlet excited state is followed by nearly quantitative intersystem crossing to the lowest fullerene triplet excited state in CH2Cl2 and toluene. whereas OPV --> C-60 electron transfer is able to compete significantly in the more polar solvent benzonitrile. In the case of B-3PV, the excited-state properties are more complex due to the electron donating ability of the pyrazoline ring. As observed for A-3PV, quantitative OPV --> C-60 photoinduced singlet-singlet energy transfer Occurs in B-3PV. However, in this case, the population of the lowest fullerene singlet excited state is followed by an efficient electron transfer from the pyrazoline ring in CH2Cl2 and benzonitrile. In B-3PV. studies of the dependence of photoinduced processes on solvent polarity. addition of acid. and temperature also reveal that this Compound can be considered as a fullerene-based molecular switch, the switchable parameters being the photoinduced processes. Finally, A-3PV and B-3PV have been tested as active materials in photovoltaic devices and the differences of light to energy conversion efficiencies found for the two compounds have been rationalised on the basis of their photophysical properties.

Abstract: New oligophenylenevinylene-terminated phenylenevinylene dendrons have been prepared and attached to C-60 by a 1,3-dipolar cycloaddition of the azomethine ylides generated in situ from the dendritic aldehydes and N-methylglycine. Preliminary photophysical investigations of the resulting fullerodendrimers have revealed interesting light-harvesting properties. (C) 2001 Published by Elsevier Science Ltd.

Abstract: The rhenium(i) and ruthemum(H) complexes of a fullerene-substituted bipyridine ligand have been prepared. Electrochemical studies indicate that so..,ne ground state electronic interaction between the fullerene subunit and the metal-complexed moiety are present in the Re-1 but not the Ru-11 complex. The photophysical properties have b.-en investigated by steady-state and time-resolved UV/Vis-NIR luminescence spectroscopy and nanosecond laser flash photolysis in CH,Cl, solution, and compared to those of the corresponding model compounds. Excitation of the methanofullerene moiety in the dyads does not lead to excited state intercomponent interactions. Instead, excitation of the metal-complexed unit shows that the lowest triplet metal-to-ligand-charge-transfer excited state ((MLCT)-M-3) centered on the Re-1- or Ru-11-type unit is quenched with a rate constant of about 2.5 x 10(8) s(-1). The quenching, is attributed to an electron-transfer (EIT) process leading to the reduction of the carbon sphere, as determined by luminescence spectroscopy for the Ru-11 dyad. Experimental detection of electron transfer in the Re-1 dyad is prevented clue to the unfavorable absorption of the metal-complexed moiety relative to the fullerene unit. However. it can tic postulated on the basis of energetic/ kinetic arguments and by comparison with the Ru-11-type array. The primary EIT process is followed by charge-recombination to give [fie lowest-lying fullerene triplet excited state (C-3(60)) with quantitative yield, as determined by sensitized singlet oxygen luminescence experiments. Direct (MLCT)-M-1 --> C-3(60) triplet-triplet energy-transfer (EnT) does not successfully compete with EIT since it is highly exoergonic and located in the Marcus inverted region. The quantum yield of singlet oxygen sensitization (P,) of the Re-1-based dyad is found to be lower (0.80) than for the cot-responding Ru-11 derivative (1.0). This is likely to be the consequence of different conformational structures for the two dyads, rather than a different yield of C-3(60) formation.

Abstract: Steady-state and time-resolved spectroscopic properties of bichromophoric species containing [Ru(bpy)(3)](2+) and pyrene (pyr) units linked together by flexible poly(ethylene glycol) chains of variable length, [Ru(bpy)(2)(bpy-pyr)]-(PF6)(2) (1) and [Ru(bpy)(2)(bpy-O6-pyr)](PF6)(2) (2), have been investigated in acetonitrile solvent. The complexes were designed with the aim of examining the intercomponent energy-transfer processes taking place after light absorption at the two chromophores and the influence of the distance separation between them; in the case of complex 2, the linking chain in the extended conformation is as long as 21 A, Direct excitation of the pyrene unit (lambda(exc) = 410 nm) results in singlet-to-singlet energy transfer (an antenna effect) to the Ru-based component, (1)pyr --> (MLCT)-M-1, which we analyze in terms of the Forster mechanism taking place with unit efficiency. Analysis of the time-resolved pyrene fluorescence reveals that the actual center-to-center distance separation (d(cc)) between the photoactive centers changes according to a Gaussian distribution, with an average d(cc) = 13.6 Angstrom (distribution width, a = 2.8 Angstrom) and 12 Angstrom (a = 10.2 Angstrom), for 1 and 2, respectively; this is ascribed to folding of the poly(ethylene glycol) linking chain. In O-2-free solvent at room temperature, after population of the (MLCT)-M-1 level (which takes place either because of direct excitation by using lambda(exc) > 355 nm or via the "antenna" effect) and subsequent intersystem crossing localized at the Ru center, (MLCT)-M-1 --> (MLCT)-M-3, a triplet-triplet thermal equilibration is established which involves the physically separated centers, (MLCT)-M-3 <----> (3)pyr, with K-eq = 11 (the energy gap between the two levels is 480 cm(-1), as determined from luminescence data obtained at 77 K). As a consequence of this equilibrium, the 3MLCT luminescence lifetime becomes tau(Ru) similar to 9 mus both in 1 and 2, i.e., 1 order of magnitude longer than for the unsubstituted [Ru(bpy)(3)](2+) luminophore. In air-equilibrated solvent, diffusional quenching by O-2 effectively depletes the (3)pyr level and only the forward (MLCT)-M-3 --> (3)pyr energy transfer stop is observed with k(en) = 4 x 10(8) and 2 x 10(8) s(-1) for 1 and 2, respectively, As briefly discussed, reasons for the high rate constants observed for the various triplet-triplet steps may be traced back to the folding properties of the linking chains.

Abstract: Dendrimers with an electroactive bis(phenanthroline) copper(I) core have been prepared and thin layer cyclic voltammetry (TLCV) found to be an efficient tool to determine their redox characteristics in spite of the slow electron transfer kinetics observed for the largest compounds.

Abstract: A two-component ligand system (1) containing 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) as the hosting unit for the lanthanide cations and an appended asymmetrically functionalized 1,10-phenanthroline (phen) as the chromophore was synthesized, The 1:1 complexes with Eu3+, Gd3+, Tb3+, and Yb3+ have been prepared and studied in aqueous solution. For Gd.1, a relaxivity value of 2.4 mM(-1) s(-1) has been measured at 20 MHz and 25degreesC, which indicates that there are no water molecules in the first coordination sphere of the metal ion. The analysis of high resolution H-1 NMR spectra of Yb.1 supports this view and suggests the direct involvement of the phen moiety in the coordination of the metal ion. For Eu.1 and Tb.1, the absorption and luminescence spectra, the overall luminescence efficiencies, and the metal-centered (MC) lifetimes were obtained; coordination features were also determined by comparing luminescence properties in water and deuterated water. For Eu.1 and Tb.1, the overall emission sensitization (se) process in air-equilibrated water was found to be notably effective with phi(se) = 0.21 and 0.11, respectively. A detailed study of the steps originating from light absorption at the phen unit and leading to MC sensitized emission was performed.

Abstract: Poly(aryl ether) dendritic branches terminated with peripheral triethyleneglycol chains have been attached to C-60. The resulting fullerodendrimers have been characterised by electrospray mass spectrometry (ESMS), which appears to be a particularly interesting analytical tool for the unambiguous structural assignment of such high molecular weight fullerene derivatives. Their photophysical properties have been systematically investigated in three solvents, namely toluene, dichloromethane, and acetonitrile. The changes observed in the photophysical properties along the series suggest an increasing interaction between the poly(aryl ether) dendritic wedges and the fullerene core, which brings about an increasing isolation of the central chromophore from the exterior. Finally, thanks to their high solubility, fullerodendrimers 1-4 have been easily incorporated in mesoporous silica glasses and preliminary measurements on the resulting doped samples have revealed efficient optical limiting properties.

Abstract: The extent of photoinduced energy-transfer between [Ru(bipy)(3)](2+) and [Os(bipy)(3)](2+) units attached to either end of a deca(oxoethylene) 33-atom chain can be used to show how the distribution of end-to-end distances in the ensemble of conformations changes in different solvents.

Abstract: The synthesis and the liquid crystalline properties of a new class of conjugated derivatives that assembled four oligophenylenevinylene (OPV) moieties arising from a calix[4]arene core are described. Photophysical investigations also revealed strong electronic coupling between the four OPV fragments of the calix[4]OPV derivative. (C) 2001 Elsevier Science Ltd. All rights reserved.

Abstract: Lanthanide(III) complexes have been prepared with [L-1](-) [the tetradentate chelating ligand bis(3-(2-pyridyl)pyrazolyl)dihydroborate], [L-2](-) [the tetradentate chelating ligand bis{3-(2-pyrazinyl)pyrazolyl}dihydroborate], [L-3](-) [the hexadentate chelating ligand bis[3-{6'-(2,2'-bipyridyl)}pyrazol-1-yl]dihydroborate], and [L-4](2-) [the 12-dentate compartmental ligand hexakis{3-(2-pyridyl)pyrazol-1-yl}diboran(IV)ate, which has two hexadentate tris(pyrazolyl)borate-based cavities linked "back-to-back" by a B-B bond]. [Ln(L-1)(2)(NO)(3)] are 10-coordinate with two tetradentate N-donor ligands and one bidentate nitrate. [Ln(L-2)(2)(NO)(3)] have 10-coordinate structures similar to those of the [L-1](-) complexes except that the coordinated N-1 of the pyrazine rings is not such a good donor as the pyridine rings in the [L-1](-) complexes, leading to marked lengthening of these Ln-N bonds. [Ln(L-3)(NO3)(2)] are also 10-coordinate from one hexadentate chelating ligand which has a pseudoequatorial coordination mode and two pseudoaxial bidentate nitrate ligands; the hexadentate ligand has a shallow helical twist to prevent steric interference between its ends. Finally [{Ln(NO3)(2)(L-4)] are dinuclear, with each metal center being 10-coordinate from a tripodal hexadentate ligand cavity and two bidentate nitrates. Five complexes were structurally characterized: [Tb(L-2)(2)(NO3)].dmf is monoclinic (P2(1)/c) with a = 14.881(3) Angstrom, b = 15.5199(12) Angstrom, c = 15.845(2) Angstrom, beta = 92.387(12)degrees, and Z = 4. [Gd(L-2)(2)(NO3)].dmf is monoclinic (P2(1)/c) with a = 14.926(2) Angstrom, b = 15.465(2) Angstrom, c 15.878(2) Angstrom, beta = 92.698(11)degrees, and Z = 4. [Eu(L-3)(NO3)(2)].dmf.0.5Et(2)O is triclinic (P (1) over bar) with a 10.020(3) Angstrom, b = 13.036(3) Angstrom, c = 14.740(3) Angstrom, alpha = 70.114(14)degrees, beta = 71.55(2)degrees, gamma = 79.66(2)degrees, and Z = 2. [{La(NO3)(dmf)(2)}(2)(L-4)](NO3)(2).dmf is orthorhombic (Pbca) with a = 18.813(2) Angstrom, b = 15.241(2) Angstrom, c = 27.322(2), and Z = 4. [{Gd(NO3)(2)}(2)(L-4)].2.4dmf is tetragonal (P4(2)/n) with a = 16.622(6), c = 24.19(5) Angstrom, and Z = 4. Detailed photophysical studies have been performed on the free ligands and their complexes with Gd(III), Eu(III), and Tb(III) in several solvents. The results show a wide range in the emission properties of the complexes which can be rationalized in terms of subtle variations in the steric and electronic properties of the ligands. In particular the dinuclear Tb(III) complex of [L-4](2-) has an emission quantum yield of ca. 0.5 in D2O and MeOD.