[60]Fullerene-flavonoid dyads

A range of fullerene-chalcone, fullerene-flavone, and fullerene-chromone dyads, including a bis(flavonyl)-fullerene dyad, were prepared by 1,3-dipolar cycloaddition reactions of azomethine ylides to C₆₀ and by cyclopropanation of C₆₀ with flavonyl malonates. Synthetic and natural flavonoid derivatives were used as starting materials.     

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.     

Synthesis and properties of isoxazolo[60]fullerene-donor dyads

A series of isoxazolo[60]fullerenes has been prepared in one pot from aldoximes under microwave irradiation. Several donors and acceptors were used as substituents. The absorption and emission spectra of these compounds in polar solvents suggest a weak charge-transfer interaction between the oxygen atom of the isoxazoline moiety and the C(60) cage, as well as a stronger interaction between the donor and the fullerene cage when the attached groups are p-N,N-dimethylaniline or ferrocene. The electrochemical properties of the compounds were investigated and they show the same or better acceptor character than C(60) in all cases. Theoretical calculations support the results obtained. Solvent effects in the (1)H NMR spectra have been determined and provide useful information concerning the polarization of dyads.     

Liquid-crystalline hybrid materials based on [60]fullerene and bent-core structures

What a core-ker! By the appropriate combination of promesogenic bent-core structures and the C(60) unit, lamellar polar liquid-crystal phases were induced. The supramolecular organization of the functional fullerene-based assemblies, the temperature range of the soft phase, the stabilization of the mesophase-like order at room temperature, and the molecular switching under an electric field can be tuned, depending on the molecular structure.     

Self-organization of phthalocyanine--[60]fullerene dyads in liquid crystals

The use of blends in which a mesogen induces mesomorphism into a non-mesogenic compound has made possible the self-organization of phthalocyanine--[60]fullerene (Pc-C60) dyads into liquid crystals. Pc-C60 dyads 1, 2, or 3, in which two photoactive units are brought together by a phenylenevinylene spacer, have been synthesized through a Heck reaction that links 4-vinylbenzaldehyde to a monoiodophthalocyanine precursor, followed by standard cycloaddition of azomethine ylides--generated from the formylPc derivative and N-methylglycine--to one of the double bonds of C60. The mesomorphic and thermal properties of different mixtures formed by the liquid-crystalline phthalocyanine 4 and dyads 1, 2, or 3 were examined using polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). DSC diagrams of the blends show clear transitions from the crystalline state to a mesophase, and the measured structural parameters obtained from the powder diffraction experiments are consistent with a discotic hexagonal columnar (Col h) structure. Considering that segregation in domains of separated molecules of Pc-C60 dyad and phthalocyanine 4 would preclude mesomorphism due to the mismatch in the column diameter and to the lack of mesogenic character of the pure dyads, a predominance of alternating stacking is proposed. Additionally, the observed decrease in the calculated density of the blend mesophases relative to the mesophase of pure compound 4 is important evidence in this direction.     

Ruthenocene as a new donor fragment in [60]fullerene-donor dyads

Four novel fullerene derivatives containing ruthenocene as the donor fragment have been synthesized and their electrochemical and fluorescence properties have been studied. Steady state fluorescence studies suggest the existence of photoinduced electron transfer in these dyads.     

Energy and electron transfer in beta-alkynyl-linked porphyrin-[60]fullerene dyads

Three porphyrin-fullerene dyads, in which a diyne bridge links C(60) with a beta-position on a tetraarylporphyrin, have been synthesized. The free-base dyad was prepared, as well as the corresponding Zn(II) and Ni(II) materials. These represent the first examples of a new class of conjugatively linked electron donor-acceptor systems in which pi-conjugation extends from the porphyrin ring system directly to the fullerene surface. The processes that occur following photoexcitation of these dyads were examined using fluorescence and transient absorption techniques on the femtosecond, picosecond, and nanosecond time scales. In sharp contrast to the photodynamics associated with singlet excited-state decay of reference tetraphenylporphyrins (ZnTPP, NiTPP, and H(2)TPP), the diyne-linked dyads undergo ultrafast (<10 ps) singlet excited-state deactivation in toluene, tetrahydrofuran (THF), and benzonitrile (PhCN). Transient absorption techniques with the ZnP-C(60) dyad clearly show that in toluene intramolecular energy transfer (EnT) to ultimately generate C(60) triplet excited states is the dominant singlet decay mechanism, while intramolecular electron transfer (ET) dominates in THF and PhCN to give the ZnP(*+)/C(60)(*-) charge-separated radical ion pair (CSRP). Electrochemical studies indicate that there is no significant charge transfer in the ground states of these systems. The lifetime of ZnP(*+)/C(60)(*-) in PhCN was approximately 40 ps, determined by two different types of transient absorption measurement in two different laboratories. Thus, in this system, the ratio of the rates for charge separation (k(CS)) to rates for charge recombination (k(CR)), k(CS)/k(CR), is quite small, approximately 7. The fact that charge separation (CS) rates increase with increasing solvent polarity is consistent with this process occurring in the normal region of the Marcus curve, while the slower charge recombination (CR) rates in less polar solvents indicate that the CR process occurs in the Marcus inverted region. While photoinduced ET occurs on a similar time scale in a related dyad 15 in which a diethynyl bridge connects C(60) to the para position of a meso phenyl moiety of a tetrarylporphyrin, CR occurs much more slowly; i.e., k(CS)/k(CR) approximately equal to 7400. Thus, the position at which the conjugative linker is attached to the porphyrin moiety has a dramatic influence on k(CR) but not on k(CS). On the basis of electron density calculations, we tentatively conclude that unfavorable orbital symmetries inhibit charge recombination in 15 vis a vis the beta-linked dyads.     

Nonlinear optical properties of ferrocene- and porphyrin-[60]fullerene dyads.

A series of novel [60]fullerene-ferrocene and [60]fullerene-porphyrin dyads, in which a fullerene and an electron donating moiety are attached through a flexible triethylene glycol linker are synthesized and their nonlinear optical (NLO) response studied. Specifically, the third-order susceptibility chi(3) of all fullerene derivatives are measured in toluene solutions by the optical Kerr effect (OKE) technique using 532 nm, 35 ps laser pulses and their second hyperpolarizability gamma are determined. All fullerene dyads studied exhibit enhancement of their NLO response compared to pristine fullerenes which has been attributed to the formation of a charge separated state. All experimentally measured hyperpolarizability gamma values are also calculated by the semiempirical methods AM1 and PM3. A good correlation is found between the theoretical and experimental values, suggesting that simple semiempirical methods can be employed for the designing and optimization of the fullerene-containing dyads displaying improved nonlinear responses.     

Photoinduced charge-separation and charge-recombination processes of fullerene[60] dyads covalently connected with phenothiazine and its trimer

Photoinduced charge-separation and charge-recombination processes of fullerene[60] dyads covalently connected with phenothiazine and its trimer (PTZ n -C 60, n = 1 and 3) with a short amide linkage were investigated. A time-resolved fluorescence study provided evidence of charge separation via the excited singlet state of a C 60 moiety ( (1)C 60*), which displayed high efficiencies in various solvents; Phi (S) CS (quantum yield of charge separation via (1)C 60*) = 0.59 (toluene) to 0.87 (DMF) for PTZ 1-C 60 and 0.78 (toluene) to 0.91 (DMF) for PTZ 3-C 60. The transient absorption measurement with a 6 ns time resolution in the visible and near-IR regions showed evidence of the generation of radical ion pairs in relatively polar solvents for both dyads. In nonpolar toluene, only PTZ 1- (3)C 60* was observed for PTZ 1-C 60, whereas PTZ 3- (3)C 60* as well as the radical ion pair state in equilibrium were observed for PTZ 3-C 60. The radical ion pairs had relatively long lifetimes: 60 (DMF) to 910 ns ( o-dichlorobenzene) for (PTZ) 1 (*+)-C 60 (*-) and 230 (PhCN) to 380 ns ( o-dichlorobenzene) for (PTZ) 3 (*+)-C 60 (*-). The small reorganization energy (lambda) and the electronic coupling element (| V|) were estimated by the temperature dependence of the charge-recombination rates, i.e., lambda = 0.53 eV and | V| = 1.6 cm (-1) for (PTZ) 3 (*+)-C 60 (*-).     

Conformation effect of oligosilane linker on photoinduced electron transfer of tetrasilane-linked zinc porphyrin–[60]fullerene dyads

A series of zinc porphyrin–[60]fullerene dyads linked by conformation-constrained tetrasilanes and permethylated tetrasilane have been synthesized for the evaluation of the conformation effect of the tetrasilane linkers on the photoinduced electron transfer. The excited-state dynamics of these dyads have been studied using the time-resolved fluorescence and absorption measurements. The fluorescence of the zinc porphyrin moiety in each dyad was quenched by the electron transfer to the fullerene moiety. The transient absorption measurements revealed that the final state of the excited-state process was a radical ion pair with a radical cation on the zinc porphyrin moiety and a radical anion on the fullerene moiety as a result of the charge separation. The charge separation and charge recombination rates were found to show only slight conformation dependence of the tetrasilane linkers, which is characteristic for the Si-linkages.     

Synthesis of diverse N,O-bridged calix[1]arene[4]pyridine-C(60) dyads and triads and formation of intramolecular self-inclusion complexes

Starting from both the bridging nitrogen atom-functionalized and the upper rim-functionalized N,O-bridged calix[1]arene[4]pyridine reactants, different types of heteracalixaromatics-C(60) dyads and triads of varied spacers were expediently synthesized using mainly the click reaction as the key step. By means of various spectroscopic methods, the heteracalixaromatics-C(60) dyads and triads obtained have been shown to form intramolecular self-inclusion complexes rather than oligomers or polymers in solution because of a flexible spacer in between the heteracalixaromatic ring and C(60) moiety. The current study, coupled with previous investigations, would provide the guideline for the construction of supramolecular fullerene motifs based on molecular design of the dyads and triads.     

Photoswitchable fluorescent dyads incorporating BODIPY and [1,3]oxazine components

We designed and synthesized three compounds incorporating a BODIPY fluorophore and an oxazine photochrome within the same molecular skeleton and differing in the nature of the linker bridging the two functional components. The [1,3]oxazine ring of the photochrome opens in less than 6 ns upon laser excitation in two of the three fluorophore-photochrome dyads. This process generates a 3H-indolium cation with a quantum yield of 0.02-0.05. The photogenerated isomer has a lifetime of 1-3 μs and reverts to the original species with first-order kinetics. Both photochromic systems tolerate hundreds of switching cycles with no sign of degradation. The visible excitation of the dyads is accompanied by the characteristic fluorescence of the BODIPY component. However, the cationic fragment of their photogenerated isomers can accept an electron or energy from the excited fluorophore. As a result, the photoinduced transformation of the photochromic component within each dyad results in the effective quenching of the BODIPY emission. Indeed, the fluorescence of these photoswitchable compounds can be modulated on a microsecond time scale with excellent fatigue resistance under optical control. Thus, our operating principles and choice of functional components can ultimately lead to the development of valuable photoswitchable fluorescent probes for the super-resolution imaging of biological samples.     

富勒烯[60]的光化学反应研究

从光物理出发,综述了近几年富勒烯「６０」的光化学反应研究进展。Ｃ６０能发生诸多的光化学反应：（１）光氧化;（２）光氢化还原;（３）「２＋２」光环化加成;（４）与叔胺的光加成;（５）与氨基酸的光加成;（６）与金属有机化合物的光加成。     

Chromophoric interactions in [60]fullerene–porphyrin dyads investigated by solid-state UV–Vis and IR spectroscopies

Solid-state electronic (UV–Vis) and vibrational (IR) spectra of several fullerene–porphyrin conjugates were recorded in KBr in the spectral range between 400 and 50,000 cm⁻¹. It was observed that significant redistribution of the charges occurs in both fullerene and porphyrin moieties upon covalent linkage. This effect is mainly observed as shifts of both electronic and vibrational bands in comparison with the respective free porphyrin and fullerene features. Variable temperature IR measurements were also performed.     

Synthesis of 4-aziridino[C60]fullerene-1,8-naphthalimide (C60-NI dyads) and their photophysical properties

A series of 4-aziridino[C₆₀]fullerene-1,8-naphthalimide (C₆₀-NI) dyads 4 ([6,6]-closed ring) were synthesized as the only addition product from the reaction of C₆₀ with the corresponding azide compounds 3 under microwave irradiation in good yield. A quenching of fluorescence was shown in dyads 4, and this decay was evidenced to be an intramolecular process.     

Photoinduced Reaction of [60]Fullerene with Tertiary Amines: Synthesis of [60]Fulleropyrrolidines

[60]Fulleropyrrolidine derivatives were prepared from the photoinduced reaction of [60]fullerene and tertiary amines.     

Probing the spatial requirements for [60]fullerene-[60]fullerene π-stacking and the syn addition of [60]fullerenes across acenes

The reaction between 2 equiv of [60]fullerene and 6,8,15,17-tetraphenylheptacene-7,16-quinone leads to both cis and trans-bis[60]fullerene adducts. This result contrasts sharply with the highly diastereoselective syn additions of [60]fullerenes across 6,13-diphenylpentacene and 6,8,15,17-tetraphenylheptacene. The importance of spatially dependent [60]fullerene-[60]fullerene π-stacking interactions in promoting a syn addition of [60]fullerenes is discussed.     

Three novel bismetallacyclopropa[60]fullerene complexes formed via intermediate monometallacyclopropa[60]fullerene diphosphine ligands

The homodinuclear bismetallacyclopropa[60]fullerene complexes (η²-C₆₀)M(μ-η¹,η¹-trans-Ph₂PCHCH PPh₂)₂M(η²-C₆₀) (1, M = Pt; 2, M = Pd) were prepared by reaction of C₆₀ with M(dba)₂ (dba = dibenzylideneacetone) and trans-1,1′-bis(diphenylphosphino)ethylene in 82% and 92% yield, whereas reaction of C₆₀ with Pd(dba)₂ and trans-dppet followed by treatment with C₆₀ and Pt₂(dba)₃ gave rise to the heterodinuclear complex (η²-C₆₀) Pd(μ-η¹,η¹-trans-Ph₂PCHCH PPh₂)₂Pt(η²-C₆₀) (3) in 65% yield. Mechanistic study showed that these reactions involve the intermediates of monometallacyclopropa[60]fullerene diphosphine ligands (η²-C₆₀)M(η¹-trans-Ph₂PCHCHPPh₂)₂ (4, M = Pt; 5, M = Pd). All the mono- and bismetallacyclopropa[60]fullerene complexes 1-5 have been fully characterized by elemental analysis and spectroscopy, as well as for 2 by X-ray crystallography.     

Synthesis of [60]fullerene-functionalized rotaxanes

Synthesis of [60]fullerene (C₆₀)-functionalized rotaxanes via Diels-Alder reactions with C₆₀ is described. Diels-Alder reaction of C₆₀ and sulfolene moiety as masked diene attached on the wheels of rotaxanes results in high yields of C₆₀ incorporation. Rotaxanes are prepared by tin-catalyzed urethane-forming end-capping reaction with isocyanate of pseudorotaxane having the wheel carrying C₆₀ functionality as introduced by the Diels-Alder reaction. The Diels-Alder reaction was accomplished as end-capping reaction between C₆₀ and pseudorotaxane bearing sultine moiety as masked diene on the axle terminal. A variety of C₆₀-containing [2]rotaxanes was prepared in moderate to good yields by these Diels-Alder protocols.