Efficient preparation of monoadducts of [60] fullerene and anthracenes by solution chemistry and their thermolytic decomposition in the solid state

Sonochemical synthesis of novel C60 fullerene 1,4-oxathiane derivative through the intermediate fullerene radical anion

We have discovered a selective and efficient method for the synthesis of previously unknown 1,9-(1',4'-oxathiano)-1,9-dihydro-(C₆₀-I_h)[5,6]fullerene, a compound with the direct attachment of the sulfur atom to the fullerene core. The method is based on the reaction of C₆₀ with 1,2-hydroxythiols in the presence of inorganic bases in air under ultrasonication. The significance of ultrasound has been exemplified with the comparative conventional methods. The title compound has been identified with mass-(MALDI TOF/TOF), one- and two-dimensional NMR ¹H and ¹³C (COSY, HSQC, HMBS), IR, UV-Vis spectroscopic techniques. Using the direct EPR method, we have detected radical anion C₆₀^- (g = 2.0046 and ΔH = 2 G) as a key reaction intermediate of the sonochemical reaction. Based on the experimental results and quantum chemical calculations, we have proposed a mechanism for the conversion of C₆₀ and 2-mercaptoethanol to the C₆₀-1,4-oxathiane adduct.

The intermolecular anthracene-transfer in a regiospecific antipodal C60 difunctionalization

Ever since the discovery of fullerenes, their mono- and multi-functionalization by exohedral addition chemistry has been a fundamental topic. A few years ago, a topochemically controlled regiospecific difunctionalization of C₆₀ fullerene by anthracene in the solid state was discovered. In the present work, we analyse the mechanism of this unique reaction, where an anthracene molecule is transferred from one C₆₀ mono-adduct to another one, under exclusive formation of equal amounts of C₆₀ and of the difficult to make, highly useful, antipodal C₆₀ bis-adduct. Our herein disclosed dispersion corrected DFT studies show the anthracene transfer to take place in a synchronous retro Diels-Alder/Diels-Alder reaction: an anthracene molecule dissociates from one fullerene under formation of an intermediate, while undergoing stabilizing interactions with both neighbouring fullerene molecules, facilitating the reaction kinetically. In the intermediate, a planar anthracene molecule is sandwiched between two neighbouring fullerenes and forms equally strong 'double-decker' type π-π stacking interactions with both of these fullerenes. Analysis with the distortion interaction model shows that the anthracene unit of the intermediate is almost planar with minimal distortion. This analysis highlights the existence of simultaneous noncovalent interactions engaging both faces of a planar polyunsaturated ring and two convex fullerene surfaces in an unprecedented 'inverted sandwich' structure. Hence, it sheds light on new strategies to design functional fullerene based materials.

Pd(II) Coordination Sphere Engineering: Pyridine Cages, Quinoline Bowls, and Heteroleptic Pills Binding One or Two Fullerenes

Fullerenes and their derivatives are of tremendous technological relevance. Synthetic access and application are still hampered by tedious purification protocols, peculiar solubility, and limited control over regioselective derivatization. We present a modular self-assembly system based on a new low-molecular-weight binding motif, appended by two palladium(II)-coordinating units of different steric demands, to either form a [Pd₂L¹₄]⁴⁺ cage or an unprecedented [Pd₂L²₃(MeCN)₂]⁴⁺ bowl (with L¹ = pyridyl, L² = quinolinyl donors). The former was used as a selective induced-fit receptor for C₆₀. The latter, owing to its more open structure, also allows binding of C₇₀ and fullerene derivatives. By exposing only a fraction of the bound guests’ surface, the bowl acts as fullerene protecting group to control functionalization, as demonstrated by exclusive monoaddition of anthracene. In a hierarchical manner, sterically low-demanding dicarboxylates were found to bridge pairs of bowls into pill-shaped dimers, able to host two fullerenes. The hosts allow transferring bound fullerenes into a variety of organic solvents, extending the scope of possible derivatization and processing methodologies.

Tailor-Made Pyrazolide-Based Metal-Organic Frameworks for Selective Catalysis

The predesignable porous structures in metal-organic frameworks (MOFs) render them quite attractive as a host-guest platform to address a variety of important issues at the frontiers of science. In this work, a perfluorophenylene functionalized metalloporphyrinic MOF, namely, PCN-624, has been rationally designed, synthesized, and structurally characterized. PCN-624 is constructed by 12-connected [Ni₈(OH)₄(H₂O)₂Pz₁₂] (Pz = pyrazolide) nodes and fluorinated 5,10,15,20-tetrakis(2,3,5,6-tetrafluoro-4-(1 H-pyrazol-4-yl)phenyl)-porphyrin (TTFPPP) linker with an ftw-a topological net. Notably, PCN-624 exhibits extinguished robustness under different conditions, including organic solvents, strong acid, and base aqueous solutions. The pore surface of PCN-624 is decorated with pendant perfluorophenylene groups. These moieties fabricate densely fluorinated nanocages resulting in the selective guest capture of the material. More importantly, PCN-624 can be employed as an efficient heterogeneous catalyst for the selective synthesis of fullerene-anthracene bisadduct. Owing to the high chemical robustness of PCN-624, it can be recycled over five times without significant loss of its catalytic activity. All of these results demonstrate that MOFs can serve as a powerful platform with great flexibility for functional design to solve various synthetic problems.

Theoretical Study on the Reactivity and Regioselectivity of the Diels-Alder Reaction of Fullerene: Effects of Charges and Encapsulated Lanthanum on the Bis-Functionalization of C70

Bis-adducts of fullerenes are important for both material and biological science. The first added substituent greatly impacts the reactivity and regioselectivity of fullerene. What determines the bond reactivity and how to control the regioselectivity are two crucial questions in synthesizing bis-adduct of C₇₀. Recently, an unexpected 12 o'clock isomer of anthracene bis-adduct of C₇₀ was prepared with high yield by the Diels-Alder (DA) reaction although three possible isomers (12, 2, and 5 o'clock isomers) may be formed. In the current study, the beneath mechanism is systematically investigated by density functional theory methods. Moreover, effects of charges and encapsulated lanthanum atom on the regioselectivity are reported. The computational results successfully rationalize experimental observations by Venkata et al. A possible way to change the regioselectivity of DA reaction is put forward. The kinetical promotion effect of an encapsulated La atom on the 12 o'clock reaction is elucidated.

Blend films of an amorphous conjugated polymer and a thermal precursor fullerene: effects of annealing temperatures on film structures and photovoltaic properties

Thermal precursor approach using C₆₀–9-methylanthracene adducts enables blend film formations with bulk heterojunction structures containing highly aggregating pristine C₆₀ molecules in combination with an amorphous conjugated polymer, PCDTBT.

Selective and reversible self-assembly of C60fullerene on a 9,10-bis(S-acetylthiomethyl)anthracene modified gold surface

Synthesized di-S-acetyl anthracene derivative deposited on gold surface allows for selective multi-cycle capture of C₆₀fullerene by reversible forming well-ordered monolayers of C₆₀fullerene–anthracene adduct according to Diels–Alder reaction.

Molecular self-healing mechanisms between C60-fullerene and anthracene unveiled by Raman and two-dimensional correlation spectroscopy

C₆₀-fullerene–anthracene self-healing copolymers were studied by time-, temperature- and concentration-dependent FT-Raman spectroscopy and advanced 2D correlation analysis.

Supramolecular control of electronic properties in aromatic materials

The use of supramolecular interactions for controlling the electronic and photophysical properties of organic π-conjugated materials is described. This leads to materials presenting unique properties, such as light-induced switching of polarization (photopolism), or the spontaneous formation of highly luminescent vesicles. In another approach, reversible covalent bonds are used to prepare densely packed fullerene monolayers whose conductivity could be probed using conducting AFM.

High-yield, regiospecific bis-functionalization of C70 using a Diels–Alder reaction in molten anthracene

A regiospecific bis-adduct of C₇₀ with anthracene was prepared with unusually high yield (68%) by the Diels–Alder reaction in the absence of solvent (melt). The structure of the bis-adduct was an unexpected 12 o'clock isomer, as determined by single crystal X-ray diffraction, thermal gravimetric analysis (TGA) and spectroscopy.

Engineering molecular chains in carbon nanotubes

A range of mono- and bis-functionalised fullerenes have been synthesised and inserted into single-walled carbon nanotubes. The effect of the size and shape of the functional groups of the fullerenes on the resultant 1D arrays formed within the nanotubes was investigated by high resolution transmission electron microscopy and X-ray diffraction. The addition of non-planar, sterically bulky chains to the fullerene cage results in highly ordered 1D structures in which the fullerenes are evenly spaced along the internal nanotube cavity. Theoretical calculations reveal that the functional groups interact with neighbouring fullerene cages to space the fullerenes evenly within the confines of the nanotube. The addition of two functional groups to opposite sides of the fullerene cages results in a further increase in the separation of the fullerene cages within the nanotubes at the cost of lower nanotube filling rates.

Linear-dendritic supramolecular complexes as nanoscale reaction vessels for "green" chemistry. Diels-Alder reactions between fullerene C60 and polycyclic aromatic hydrocarbons in aqueous medium

This study describes the first Diels-Alder (DA) reaction performed in aqueous medium with highly hydrophobic compounds-fullerene (C 60) as the dienophile and anthracene (An) or tetracene (Tet) as the dienes, respectively. The reactions are performed in nanocontainers, constructed by self-assembly of linear-dendritic amphiphilic copolymers with poly(ethylene glycol), PEG or poly(ethylene oxide), PEO as the hydrophilic blocks and poly(benzyl ether) monodendrons as the hydrophobic fragments: G3PEO13k, dG3 and dG2. Comparative studies under identical conditions are carried out with an amphiphilic linear-linear copolymer, poly(styrene)1800- block-PEO2100, PSt-PEO, and the nonionic surfactant Igepal CO-720, IP720. The binding affinity of supermolecules built of these amphiphiles toward the DA reagents decreases in the following order: G3PEO13k > dG3 > PSt-PEO > dG2 > IP720. The kinetic constant of binding is evaluated for tetracene and decreases in a similar fashion: 5 x 10 (-7) M/min (G3PEO13k), through 4 x 10 (-7) M/min (PSt-PEO) down to 1.5 x 10 (-7) M/min for IP720. The mobility of substrates encapsulated in the micellar core, estimated by pyrene fluorescence decay, is 95-121 ns for the micelles of the linear-dendritic copolymers and notably higher for PSt-PEO (152 ns), revealing the much denser interior of the linear analogue. The apparent kinetic constant for the DA reaction of C 60 and Tet within the G3PEO13k supermolecule in aqueous medium is markedly higher than in organic solvent (toluene), 208 vs 1.82 M /min. With G3PEO13k the conversions reach 49% for the DA reaction between C 60 and An, and 55% for C 60 and Tet. Besides the monoadduct (26.5% yield) the reaction with An produces exclusively increasing amounts of D 2 h -symmetric antipodal bis-adduct, whose yield reaches up to 22.5% after 48 h. In addition to the environmentally friendly conditions notable advantages of the synthetic strategy described are the extended stability of the linear-dendritic nanovessels, the easy collection of the products formed, and the recovery and reuse of unreacted reagents and linear-dendritic copolymers.

Kinetic Substituent and Solvent Effects in 1,3-Dipolar Cycloaddition of Diphenyldiazomethanes with Fullerenes C60 and C70: A Comparison with the Addition to TCNE, DDQ, and Chloranil

Kinetics of 1,3-dipolar cycloaddition of a series of meta- and para-substituted diphenyldiazomethanes (DDMs) with fullerenes C60 and C70 as dipolarophiles have been investigated in toluene at 30 degrees C. Fullerene C60 was ca. 1.5 times more reactive than C70. The rate constants (k) for the primary [3 + 2] additions increased with the increase of the electron-releasing ability of the meta and para substituent. The log k/k0 values were well correlated by the Yukawa-Tsuno (Y-T) equations with the smaller negative rho values (-1.6 and -1.7 for C60 and C70) and the reduced resonance reaction constants r (0.22 and 0.17) compared to similar reactions of common acceptors, TCNE, DDQ, and chloranil (CA). The plots of log k (acceptor) versus log k (C60) as reference gave good regression equations and the slopes became larger in the order of TCNE > DDQ > CA > C70 > or = C60. The rates were also found to decrease with the increase of solvent polarity due to the ground-state solvation of fullerenes. However, the relative reactivity of these acceptors toward the unsubstituted DDM increased in the order of DDQ > C60 > or = C70 > TCNE > CA. The unexpected higher reactivity of fullerenes was interpreted in terms of the inherent steric strain by the pyramidalization of the sp2 C-atoms as well as the shorter [6,6] bonds with larger pi-electron densities.

Retrocyclopropanation reactions of fullerenes: complete product analyses

Mono- and bis-pyrene malonates 1 and 2 were synthesized and reacted with C(60) to prepare the corresponding Bingel adducts 3 and 4. These compounds were characterized electrochemically and exhibited the well-established retrocyclopropanation reaction when subjected to bulk electrolytic reductions. For the first time, it was possible to perform detailed product analyses after the retrocyclopropanation reactions, and these showed the presence of the original malonates 1 and 2 along with C(60), in reasonable yields, around 50%.