Molecular panels for energy transduction in C60-based conjugates

Light-harvesting C(60)-based dyads endowed with a truxene fluorophore unit have been synthesized. Their photophysical studies in solution reveal a singlet-singlet energy transfer deactivation mechanism that confirms the actuation of the latter as an efficient molecular panel for light absorption and energy transduction. Those processes strongly depend on the nature of the linker connecting both chromophores, such as C(60) and truxene, owing to the overlapping degree between their respective orbitals. [structure: see text]     

Molecular and supramolecular organization of star-shaped C60-fullerene-containing polyethylene oxide in benzene

The molecular properties and self-organization of star-shaped fullerene-containing polyethylene oxide in benzene were studied by methods of molecular hydrodynamics and small-angle neutron scattering.     

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

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

Photochemistry of supramolecular systems containing C60

Fullerenes have been used successfully in the covalent assembly of supramolecular systems that mimic some of the electron transfer steps of photosynthetic reaction centers. In these constructs C60 is most often used as the primary electron acceptor; it is linked to cyclic tetrapyrroles or other chromophores which act as primary electron donors in photoinduced electron transfer processes. In artificial photosynthetic systems, fullerenes exhibit several differences from the superficially more biomimetic quinone electron acceptors. The lifetime of the initial charge-separated state in fullerene-based molecules is, in general, considerably longer than in comparable systems containing quinones. Moreover, photoinduced electron transfer processes take place in non-polar solvents and at low temperature in frozen glasses in a number of fullerene-based dyads and triads. These features are unusual in photosynthetic model systems that employ electron acceptors such as quinones, and are more reminiscent of electron transfer in natural reaction centers. This behavior can be attributed to a reduced sensitivity of the fullerene radical anion to solvent charge stabilization effects and small internal and solvent reorganization energies for electron transfer in the fullerene systems, relative to quinone-based systems.     

A supramolecular cup-and-ball C60-porphyrin conjugate system

In addition to the ammonium-crown ether recognition, pi-stacking interactions between the C60 sphere and the porphyrin moiety have been evidenced in a supramolecular complex obtained from a porphyrin-crown ether conjugate and a fullerene derivative bearing an ammonium unit.     

Synthesis and surface self-assembly of [3]rotaxane-porphyrin conjugates: toward the development of a supramolecular surface tweezer for C60

Surface immobilization of pristine C60 by supramolecular interactions is an attractive way to introduce C60 on surfaces since the pi-electron network and the electronic properties of C60 remain intact. Several hosts have been developed for surface complexation of C60. With few exceptions, the hosts reported to date are "electronically inert", limiting the potential applications of pristine C60-based devices. In this study, we present the synthesis and self-assembly of a potential tweezer-like host for C60 having a light-harvesting moiety and an electron-donating unit. More precisely, an azide-containing [3]rotaxane scaffold having ferrocene moieties as blocking group and thioctic acid as anchoring group for a gold surface has been synthesized. This [3]rotaxane has been self-assembled on gold in its protonated (NH2+) (1p) and neutral (NH) (1n) forms and characterized using electrochemistry, XPS, and contact angle measurements. The SAMs were functionalized with free-base and zinc porphyrin using copper-catalyzed 1,3-dipolar cycloaddition in optimized conditions. In combination with C60, this new host is expected to form a triad that could potentially be used as active building block in the preparation of nanostructured electrodes for photoelectrochemical application.     

Reducing ability of supramolecular C60 dianion toward C=O, C=C and N-N bonds

Different from C60 dianion which readily reacts with electrophiles, supramolecular C60 dianion (2) generated from gamma-cyclodextrin-bicapped C60 (1) and NaBH4 (or diborate) in DMSO-H2O (9:1, v/v) is able to reduce N-N+, C=C-EWG and C=O bonds to provide the respective dihydro derivatives; 1-mediated reduction of acetophenone with NaBH4 in the presence of (Me2N)2CH2 and EtONa gives turn over frequency (TOF)/h of 400.     

A liquid crystalline supramolecular complex of C60 with a cyclotriveratrylene derivative

Cyclotriveratrylene (CTV) derivatives substituted with 9 (1) or 18 (2) long alkyl chains have been prepared. Whereas no liquid crystalline behavior has been observed for 1, the CTV derivative 2 has mesomorphic properties. Indeed, at room temperature compound 2 exhibits a nematic phase characterized by cybotactic groups with a local lamello-columnar order. Both CTV derivatives 1 and 2 are able to form supramolecular complexes with C60 in the solid state. In both cases, the 2:1 host-guest species have been obtained as brown compounds. No liquid crystalline behavior was observed for the supramolecular complex [C60 is included in (1)2]. In contrast, observation of the brown product obtained from C60 and the CTV derivative 2 directly after preparation by polarized optical microscopy revealed a fluid birefringent phase at room temperature. When the sample is heated above 70 degrees C, the birefringence of the texture under the microscope disappears and the X-ray diffraction pattern is transformed into a pattern characteristic of a cubic phase. For the first time in thermotropic liquid crystals, the space group of this cubic phase can be assigned as I4(1)32.     

Flowerlike supramolecular architectures assembled from C60 equipped with a pyridine substituent

Fullerene (C(60))-rich and photoconductive flowerlike supramolecular assembly was constructed from self-organization of pyridine substituted C(60) by a facile drop-casting method.     

Interfacial supramolecular self-assembled monolayers of C(60) by thiolated beta-cyclodextrin on gold surfaces via monoanionic C(60)

The supramolecular self-assembled monolayers (SAMs) of C(60) by thiolated beta-cyclodextrin (CD) on gold surfaces were constructed for the first time using C(60) monoanion. The results indicate that monoanionic C(60) plays a crucial role in the formation of the C(60)-containing self-assembled monolayers. The generation of C(60) monoanion and the formation process of C(60) SAMs were monitored in-situ by UV-visible and near-IR spectroscopy. The resulting C(60) SAMs were fully characterized by spectroscopic ellipsometry (SE), cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and water contact angle measurements. After the immobilization of C(60) by the SAMs of thiolated beta-CD, the film thickness increased by approximately 1 nm from 0.8 to 1.8 nm as determined by SE, demonstrating the formation of the supramolecular self-assembled monolayers of thiolated beta-CD/C(60). The new C(60) SAMs exhibited one quasi-reversible redox couple at half wave potential of -0.57 V vs SCE in aqueous solution containing 0.1 M KCl. The surface coverage of C(60) on the gold surfaces was estimated to be 1.1 x 10(-10) mol cm(-2). The XPS showed the assembly of C(60) over the thiolated beta-CD SAMs. The surface hydrophobicity increased greatly upon the formation of the C(60)-containing SAMs as analyzed by water contact angle measurements. The results are in agreement with the formation of 1:1 complex of C(60) and cyclodextrin on gold surfaces, though it also reveals some non-homogeneous features of the monolayers.     

Well-defined self-assembling supramolecular structures in water containing a small amount of C60

In this communication, we report for the first time on the spherical bilayer vesicle formation of a dendritic C(60)-amphiphile-surfactant hybrid in aqueous solutions.     

Molecular complexes of C60 with tetrasulfur tetranitride

Compounds C₆₀(S₄N₄)_2−x (C₆H₆) _x (1a-d) withx=0.67 (a), 1.0 (b), 1.1 (c), and 1.2 (d), in which isomorphous replacement of S₄N₄ with benzene takes place, were obtained by the reaction of fullerence C₆₀ with tetrasulfur tetranitride in benzene. Complexes C₆₀·S₄N₄ (2) and C₆₀(S₄N₄)₂ (3) containing no solvent were isolated from toluene. The compositions of the compounds were established by elemental and thermogravimetric analyses. The data of IR and X-ray photoelectron (XP) spectroscopies show that in the complexes studied the transfer of electron density occurs mainly from the nitrogen atoms of S₄N₄. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 37–40. January 1977.     

An Organic Molecular Nanobarrel that Hosts and Solubilizes C60

Organic cages have gained increasing attention in recent years as molecular hosts and porous materials. Among these, barrel-shaped cages or molecular nanobarrels are promising systems to encapsulate large hosts as they possess windows of the same size as their internal cavity. However, these systems have received little attention and remain practically unexplored despite their potential. Herein, we report the design and synthesis of a new trigonal prismatic organic nanobarrel with two large triangular windows with a diameter of 12.7 Å optimal for the encapsulation of C₆₀. Remarkably, this organic nanobarrel shows a high affinity for C₆₀ in solvents in which C₆₀ is virtually insoluble, providing stable solutions of C₆₀.     

3:1 Molecular Complex of Hydroquinone and C60

The preparation of a 3:1 complex of hydroquinone (HQ) and C₆₀, (HQ)₃C₆₀, is reported and its X-ray crystal structure described. The HQ host builds up a single H-bonded super-polonium network with super-cubes as building blocks, which accommodate the large C₆₀ guest molecules. The enclathration of C₆₀ is rather tight (high density of the complex) owing, in part, to favorable charge-transfer host-guest interactions (π-donor-acceptor complex). Nonetheless, the C₆₀ molecules arc orientationally disordered, and no individual bond lengths could be measured. In contrast, the HQ host network is essentially ordered and well-defined with normal intramolecular geometry. No appreciable (powder) conductivity could be observed for (HQ)₃C₆₀, yet ESR spectra of single crystals showed interesting narrow signals.     

Absorption spectrophotometric, fluorescence and theoretical investigations on supramolecular interaction of a designed bisporphyrin with C60 and C70

The present article reports the spectroscopic and theoretical investigations on supramolecular interaction between fullerenes (C(60) and C(70)) and a designed bisporphyrin, namely 1, in toluene. Job's method of continuous variation establishes 1:1 stoichiometry of the fullerene/1 complexes. Both absorption spectrophotometric and steady-state fluorescence studies reveal effective and selective interaction between fullerenes and 1 as average binding constants (K) for the C(60)/1 and C(70)/1 complexes are enumerated to be 34,700 and 359,925 dm(3) mol(-1), respectively. Large selectivity ratio in K, i.e., K(C(70))/K(C(60)), indicates that 1 acts as an effective molecular tweezers for C(70) in solution. Time-resolved fluorescence study evokes that the quenching of fluorescence of 1 by fullerenes is of static type in nature. Molecular mechanics calculations in vacuo determine the energies and single projection structures of the supramolecular systems, which provide very good support in favor of strong binding between C(70) and 1.     

Coverage dependent supramolecular structures: C60:ACA monolayers on Ag(111)

The dependence of supramolecular structure on fractional molecular coverage has been investigated for acridine-9-carboxylic acid (ACA) and the C(60):ACA binary molecular system. The coverage-dependent phase diagram for ACA is first determined from room-temperature STM imaging. At low molecular coverages (theta < 0.4 ML, ML = monolayer), ACA forms a 2-D gas phase. Ordered ACA structures appear with increasing coverage: first a chain structure composed of ACA molecules linked by consecutive O-H...N hydrogen bonds (theta > 0.4 ML), then a dimer structure composed of ACA dimers linked by paired carboxyl-carboxyl hydrogen bonds (theta approximately equal to 1.0 ML). Structures of the C(60):ACA binary system depend on the coverage of predeposited ACA. At intermediate (0.4 ML approximately 0.8 ML) ACA coverages, C(60) deposition results in a hexagonal cooperative structure with the C(60) periodicity nearly 3 times that of the normal C(60) 2-D packing of 1 nm and exists in enantiopure domains. At higher ACA coverages, a C(60) quasi-chain structure is formed in which parallel C(60) chains are spaced by ACA dimer domains. The mechanistic role of the initial ACA phase in the formation of C(60):ACA supramolecular structures is described. Chemically intuitive molecular packing models are presented based on the observed STM images.     

C60晶体在有序相的分子取向结构

以C60晶体中分子两种取向排列形成的双能级系统为基础,通过探讨C60晶体在有序相的热力学性质,得到了38o和98o两种取向排列的分子在晶体中均匀分布的结构稳定性结论.根据已报道的C60晶体在有序相两端点温度85 K 和260 K取向分布的实验结果,将较高的分子取向(38o)能级的概率转化成分数值1/6和3/8,得到了有序相两种取向分子在两温度端点的分布规律.当概率的分数值为1/4和1/3时,C60晶体将具有较大的结构稳定性和较小的介电损耗及内耗值,对应的温度分别为122.6和194.3 K.因而解释了介电实验结果出现异常的现象是由38o取向分子均匀分布的"规则-无规-规则"变化所造成的.