A dendrimer bearing two cyclam units linked by an azobenzene moiety, and luminescent naphthalene units at the periphery performs three different functions (light-harvesting, photoisomerization and coordination of metal ions) which can cooperate or interfere depending on the nature of the metal ion. It is thus an example of light controlled molecular tweezers in which Zn(II) coordination allows 100% efficient photosensitization of azobenzene switching, while Cu(II) shuts down azobenzene isomerization.

The sphere-shaped fullerene has attracted considerable interest not least due to the peculiar electronic properties of this carbon allotrope and the fascinating materials emanating from fullerene-derived structures. The rapid development and tremendous advances in organic chemistry allow nowadays the modification of C60 to a great extent by pure chemical means. It is therefore not surprising that the fullerene moiety has also been part of dendrimers. At the initial stage, fullerenes have been examined at the center of the dendritic structure mainly aimed at possible shielding effects as exerted by the dendritic environment and light-harvesting effects due to multiple chromophores located at the periphery of the dendrimer. In recent years, also many research efforts have been devoted towards fullerene-rich nanohybrids containing multiple C60 units in the branches and/or as surface functional groups. In this review, synthetic efforts towards the construction of dendritic fullerene-rich nanostructures have been compiled and will be summarized herein.

A new series of homoleptic metallodendrimers has been synthesized through ruthenium-metal complexation by dendritically modified bathophenanthroline ligands. The presence of hydrophilic oligo(ethylene glycol) groups on the surface of the monodisperse metal complexes enabled the solubilization of all of the fractal species in a wide range of solvents, including water. The specific properties of all of these compounds have been systematically investigated by using photophysical techniques as a function of the generation number. Accordingly, the encapsulation of the highly luminescent [Ru(dpp)(3)](2+)-type (dpp=4,7-diphenyl-1,10-phenanthroline) core unit within a dendritic microenvironment creates a powerful means to shield the center from dioxygen quenching. This shielding effect, as exerted on the phosphorescent ruthenium-derived center, is reflected by enhanced emission intensities and extended excited-state lifetimes that are close to the highest values reported so far, even in an air-equilibrated aqueous medium. Interestingly, when inspecting the largest dendritic assembly, that is, the third-generation assembly, significant drops in emission quantum yields and lifetimes are observed. This anomalous behavior has been attributed to the folding of the branches towards the luminescent core.

Internal dynamics of dansylated poly(propyleneamine) dendrimers (POPAM, G1-G4) in Solution and excitation energy transfer from dansyls to eosin in POPAM-eosin complexes have been Studied by time-resolved fluorescence spectroscopy and molecular dynamics (MD) simulations. Combining the results from fluorescence anisotropy and the MD simulation studies Suggests three time domains for the internal dynamics of the G3 and G4 generations, about 60 ps for motions of the outer-sphere dansyls, 500-1000 ps for restricted motions of back-folded dansyls, and 1500-2600 ps For the overall rotation. For the smaller generations, the contribution from the restricted motions was not entirely evident. Eosin binding hinders fast rotation of the dansyl fragments in the largest G4 dendrimer, but the motion of back-folded dansyls is more hindered in the pure dendrimer. Both fluorescence anisotropy and MD results for the G4 dendrimer support the "soft" dendrimer picture with almost free mobility and substantial back-folding of the dansyls of the dendrimers in Solution. Analysis of time-dependent spectral shifts of fluorescence reveals 20-30 ps excited-state solvation relaxation around a single dansyl of a dendrimer. Dendrimer-independent excitation energy transfer from 4 to 8 ps from dansyls to eosins in POPAM-eosin complexes G2-G4 was observed.

We have investigated the self-assembly of three luminescent species in CH(3)CN/CH(2)Cl(2), namely: 1) a polylysin dendrimer (D) composed of 21 aliphatic amide units and 24 green luminescent dansyl chromophores at the periphery, 2) a molecular clip (C) with two blue luminescent anthracene sidewalls and a benzene bridging unit that bears two sulfate groups in the para position, and 3) a near infrared (NIR)-emitting Nd(3+) ion. For purposes of comparison, analogous systems have also been investigated in which Gd(3+) replaced Nd(3+). The dendrimer and the clip can bind Nd(3+) ions with formation of [D.2Nd(3+)] and [C.Nd(3+)] complexes, in which energy transfer from dansyl and, respectively, anthracene to Nd(3+) ion takes place with 65 and 8% efficiency, in air-equilibrated solution. In the case of [C.Nd(3+)], the energy-transfer efficiency is quenched by dioxygen, thereby showing that the energy donor is the lowest triplet excited state of anthracene. In [D.2Nd(3+)] the intrinsic emission efficiency of Nd(3+) is much higher (ca. 5 times) than in [C.Nd(3+)] because of a better protection of the excited lanthanide ion towards nonradiative deactivation caused by interaction with solvent molecules. By mixing solutions of D, Nd(3+), and C with proper concentrations, a supramolecular structure with five components of three different species, [D.2Nd(3+).2C], is formed. The excitation light absorbed by the clips is transferred with 100% efficiency to the dansyl units of the dendrimer and then to the Nd(3+) ions with 65% efficiency either in the presence or absence of dioxygen. These results show that the [D.2Nd(3+).2C] complex is able to efficiently harvest UV light by the 24 dansyl units of the dendrimer and the four anthracene chromophores of the two clips, and efficiently transfer it to the encapsulated Nd(3+) ions that emit in the NIR spectral region.

We have synthesized two cyclam-cored dendrimers appended with dendrons of two different types by proper protection/deprotection of the cyclam unit. The resulting dendrimers contain six naphthyl and two dansyl units (N6 D2) or two dansyl and six naphthyl units (N2 D6) at the periphery. Their photophysical properties have been compared to those of a dendrimer containing 8 dansyl units (D8) and a previously investigated dendrimer containing 8 naphthyl units (N8). The absorption spectra are those expected on the basis of the number of chromophores, demonstrating that no ground state interaction takes place. The emission spectra of N2 D6 and N6 D2 show naphthalene localized and naphthalene excimer emission similar to those observed in the case of N8, together with a much stronger dansyl emission with maximum at 525 nm. Addition of CF(3)SO(3)H to dendrimer solutions in CH(3)CN/CH(2)Cl(2) 1:1 (v/v) leads to protonation of the aliphatic amine units of the cyclam core at first and then of the aromatic amine of each dansyl chromophores. Cyclam can be diprotonated and this affects dansyl absorption and, most significantly, emission bands by a charge perturbation effect. Each dansyl unit is independently protonated in both dendrimers. The most interesting photophysical feature of these heterofunctionalized cyclam-cored dendrimers is the occurrence of an intradendrimer photoinduced energy transfer from naphthyl to dansyl chromophores of two different dendrons (interdendron mechanism). The efficiency of this process is 50 % for N6 D2 and it can be increased up to 75 % upon protonation of the cyclam core and formation of N6 D2(2H(+)). This arises from the fact that protonation of the amine units of the cyclam prevents formation of exciplexes upon naphthyl excitation, thus shutting down one of the deactivation processes of the fluorescent naphthyl excited state.

Zn(II) complexation drives the formation of a light-harvesting antenna constituted by two multicomponent luminescent ligands: a cyclam-cored dendrimer decorated at the periphery with 16 naphthyl units and an anthracene-based molecular clip.

Metallodendrimers built around a [Ru(dpp)(3)](2+)-type core (dpp = 4,7-diphenyl-1,10-phenanthroline) were prepared containing peripheral phenyl moieties. The convergent synthesis of the ligands was accomplished by coupling dendritic branches with a focal amino function to the chelating phenanthroline precursor under the formation of sulfonamide linkages. Complexation of ruthenium ions afforded the corresponding metallodendrimers with up to 24 peripheral phenyl units in the case of the largest dendritic structure. The absorption spectra and luminescence properties of the four new dendrimers are reported. The dendritic effect is clearly visible, going from zero to second generation, as demonstrated by an elongation in the excited-state lifetime in aerated acetonitrile and improved emission quantum yields relative to the reference complex containing a [Ru(dpp)(3)](2+) core. Interestingly, the use of rigid and conjugated ruthenium-based cores results, for all dendritic structures, in luminescence lifetimes that are several microseconds long in deaerated solutions, even at room temperature. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

We have synthesized the water-soluble molecular clip AC containing two anthracene sidewalls connected by semirigid aliphatic units to a benzene bridge which carries two sodium sulfate substituents. For comparison purposes, the analogous clip NC with naphthalene instead of anthracene sidewalls has been synthesized. In methanol solution both clips exist in their monomeric form, while in aqueous solution the anthracene clips AC self-assemble to give a highly stable dimer with log K-dim = 5.1 (for the naphthalene clip NC, log K-dim = 2.5). The H-1 NMR spectra of the dimers have evidenced the interaction of two intertwined clip molecules in a perpendicular arrangement. The non-associated clip AC exhibits a very strong blue fluorescence typical of the anthracene chromophoric unit. The (AC)(2) dimer has a broader absorption spectrum and a much weaker and red shifted emission band. Addition of acetylcholine leads to the disruption of the dimer (AC)(2) and the revival of the very strong fluorescence typical of the monomeric clip AC. Both clips interact with nicotinamide adenine dinucleotide (NAD(+)) in buffered aqueous solution at pH = 7.2. A H-1 NMR analysis shows that the naphthalene clip NC forms a 1 : 1 complex with NAD(+) including the active site of the cofactor inside the clip cavity. In methanol, formation of a stable 1 : 1 adduct between AC and a fluorescent first-generation dendrimer containing four dansyl groups appended to a 1,4-diaminobutane core is driven by acid addition. In such adduct, a very efficient energy transfer takes place from the excited anthracene units of the clip to the dansyl chromophores of the dendrimer. The adduct can be reversibly disassembled by addition of base or of competitive guests.

Despite their rigid scaffold, tetralactam macrocycles (TLMs) display a remarkable degree of conformational flexibility, as revealed by analysis of the corresponding X-ray crystal structures. This flexibility is not limited to the rotatability of the TLM amide groups but also applies to the m-xylene rings, and it thus has a great impact on the overall shape of the macrocycle cavity. The conformational properties of the TLMs give rise to a broad variety of intermolecular hydrogen-bonding patterns, including infinite ladders, an interesting catemer motif, and short C-HO=C hydrogen bonds. These results are in accord with previous theoretical calculations, support a structural model proposed earlier for an interpretation of scanning tunneling microscopy images, and substantially contribute to the understanding of the adaptability of macrocyclic scaffolds, which is crucial for guest binding or templated syntheses with TLMs.

We have studied internal dynamics of dansylated poly(propyleneamine) dendrimers of different generations in solution and excitation energy transfer from dansyl chromophores to xanthene dyes that form van der Waals complexes with the dendrimers

This chapter contains sections titled: Introduction Catalysis, membrane technology Pigments, adhesives, additives in chemical materials Dendrimers for displays and (opto)electronics Biomimetics, sensor technology, diagnostics (fluorescence) Dendrimers in medical diagnostics Medical applications Dendrimers in nanotechnology Bibliography and Notes for Chapter 8 "Special properties and potential applications"

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Monolayers of a large tetralactam macrocycle were prepared by vacuum sublimation oil the Au(111) surface and investigated by scanning tunnelling microscopy. The macrocycles form three different highly ordered monolayer structures alpha, beta, and eta. The alpha and P structure are stable at room temperature and call be understood as two dimensional networks which are held together by hydrogen bonds between the next neighbour molecules, These structures were described in detail before [Kossev et al.. Adv. Mat. 17, 513 (2007)]. The third structure, which is described here, is only observed after heating at 400 K and rapid cooling to low temperatures. It consists of chiral aggregates, composed of three molecules. These aggregates are either left or right handed. The surface is covered by a racemic mixture of long range ordered domains with either left or right handed aggregates.

A family of poly(propylene amine) dendrimers, decorated at their periphery with 4, 16, and 32 dansyl units and a molecular clip, composed of two anthracene sidewalls and a disulfate benzene bridging unit, show intense UV absorption and strong fluorescence in the visible region when in a CH(3)CN/CH(2)Cl(2) (1:1, v/v) solvent mixture. Both these classes of compounds are good ligands for Zn(II) ions, as demonstrated by the changes in the absorption and fluorescence spectra upon addition of metal ions. These coordinating properties have been exploited in the self-assembly of complex structures in which the interaction between a dansylated dendrimer and anthracene-functionalized clips is mediated by Zn(II) ions. The self-assembly process is reversible and the number of metal ions and molecular clips associated with each dendrimer increases with the generation number. In these adducts, an energy transfer process from the anthracene to yield the fluorescent excited state of dansyl takes place with almost unitary efficiency.

We have studied the adduct formed by N,N'-2,7-didecyldiazapyrenium (P2+), as the hexafluorophosphate salt, with a third generation dendrimer (D) that comprises 14 tertiary amine units in the interior, and 16 naphthyl and 16 trans-azobenzene units in the periphery. A strong charge-transfer interaction between the electron-accepting diazapyrenium dication and electron-donating amine units of the dendrimer interior leads to a host-guest complex with 1 : 1 stoichiometry, namely D(16t) superset of P2+. The self-assembly process can be easily monitored by strong changes in the absorption and emission spectra: (i) new absorption bands (lambda(max) approximate to 445 and 565 nm) at lower energy compared to the isolated species arise, (ii) a strong quenching of the intense diazapyrenium fluorescence is observed, and (iii) a new broad emission band, typical of the charge-transfer complex, appears with a maximum at 660 nm at 298 K and 600 nm at 77 K. By global analysis of the absorption spectra, an association constant of 1.0 x 10(6) M-1 is obtained for D(16t) superset of P2+, compared to 3.0 x 10(4) M-1 in the case of the adduct of P2+ with triethylamine under the same experimental conditions. This result demonstrates that the presence of bulky substituents at the dendrimer periphery does not hinder the formation of a stable complex and suggests a cooperative effect due to the multiple amine groups of the dendrimer branching points. No energy transfer from the azobenzene or naphthyl chromophores to the charge-transfer complex has been evidenced. The self-assembly process can be reversed upon addition of an equimolar amount of trifluoromethanesulfonic acid. An adduct with 1 : 1 stoichiometry is formed also between P2+ and D(2t14c), a species obtained from D(16t) upon irradiation at 365 nm: the corresponding association constant is very similar to that of D(16t) superset of P2+, showing that the isomeric state of the peripheral azobenzene units does not a effect the stability of the adduct.

Hydrophilic oxybathophenanthroline dendrons (generation 1-3) have been synthesized by treatment of 4,7-bis(4'-hydroxyphenyl)-1,10-phenanthroline with the corresponding bromo-functionalized etheraryl branching units containing triethylene glycol monomethyl end groups. Radiotracer experiments using Cu-64 prove the rapid formation of stable copper(II) complexes in aqueous solution. These Cu-64 complexes remain unchanged even upon addition of a high excess of glutathione as competing ligand, thus demonstrating the high stability of the formed copper(II) complexes. Electronic and EPR spectroscopy indicate the formation of [Cu(L)(2)(OH2)(2)](2+) (L = ligand) complexes in aqueous solution, confirmed by time-resolved laser fluorescence spectroscopy and supported by molecular mechanics modeling.