UV-Vis, fluorescence and NMR spectroscopic investigations on inclusion properties of a designed tetrahomocalix[8]arene with fullerenes C60 and C70 in solution

The present article reports the spectroscopic investigations on non-covalent interaction of fullerenes C(60) and C(70) with a macrocyclic receptor molecule, namely, 1,3,5,7-tetrahomo-p-tert-butylcalix[8]arene (1) in toluene. Jobs method of continuous variation reveals 1:1 stoichiometry for the fullerene complexes of 1. The most fascinating feature of the present study is that 1 binds selectively C(60) compared to C(70) as obtained from binding constant (K) data of C(60)-1 (K(C60-1)) and C(70)-1 (K(C70-1)) complexes which are enumerated to be 265,000 dm(3) mol(-1) and 63,43 dm(3) mol(-1), respectively, and selectivity in binding (K(C60-1)/K(C70-1)) is estimated to be 4.18 as obtained from UV-Vis study. Steady state fluorescence studies reveal quenching of fluorescence of 1 in presence of fullerenes and the K value of the C(60)-1 and C(70)-1 complexes are estimated to be 80,760 and 68,780 dm(3) mol(-1), respectively, with selectivity in binding (K(C60-1)/K(C70-1)) ~1.18. (1)H NMR analysis provides very good support in favor of strong binding between C(60) and 1. The high value of K value for C(60)-1 complex indicates that 1 forms an inclusion complex with C(60).     

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.     

Balancing binding strength and charge transfer lifetime in supramolecular associates of fullerenes

A macrocyclic exTTF host for fullerenes offers control over the electronic coupling between an electron donor and an acceptor, and stabilizes the charge separated state lifetimes into the range of 500 ps.     

A highly C70 selective shape-persistent rectangular prism constructed through one-step alkyne metathesis

Dynamic covalent chemistry (DCC) provides an intriguing and highly efficient approach for building molecules that are usually thermodynamically favored. However, the DCC methods that are efficient enough to construct large, complex molecules, particularly those with three-dimensional (3-D) architectures, are still very limited. Here, for the first time, we have successfully utilized alkyne metathesis, a highly efficient DCC approach, to construct the novel 3-D rectangular prismatic molecular cage COP-5 in one step from a readily accessible porphyrin-based precursor. COP-5 consists of rigid, aromatic porphyrin and carbazole moieties as well as linear ethynylene linkers, rendering its shape-persistent nature. Interestingly, COP-5 serves as an excellent receptor for fullerenes. It forms 1:1 complexes with C(60) and C(70) with association constants of 1.4 × 10(5) M(-1) (C(60)) and 1.5 × 10(8) M(-1) (C(70)) in toluene. This represents one of the highest binding affinities reported so far for purely organic fullerene receptors. COP-5 shows an unprecedented high selectivity in binding C(70) over C(60) (K(C70)/K(C60) > 1000). Moreover, the binding between the cage and fullerene is fully reversible under the acid-base stimuli, thus allowing successful separation of C(70) from a C(60)-enriched fullerene mixture (C(60)/C(70), 10/1 mol/mol) through the "selective complexation-decomplexation" strategy.     

Photophysical and theoretical insights on non-covalently linked fullerene-zinc phthalocyanine complexes

The photo-physical aspects of non-covalently linked assemblies of a series of fullerenes, namely, C60, C70, tert-butyl-(1,2-methanofullerene)-61-carboxylate (1) and [6,6]-phenyl C70 butyric acid methyl ester (2) with a designed zinc phthalocyanine (ZnPc), viz., zinc-1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (3) in toluene medium are studied employing absorption spectrophotometric, steady state and time resolved fluorescence spectroscopic measurements. Of central interest in these investigations is the preferential binding of various fullerenes with ZnPc in toluene. The ground state interaction between fullerenes and 3 is first evidenced from UV-Vis measurements. Steady state fluorescence experiment reveals efficient quenching of the excited singlet state of 3 in presence of both underivatized and derivatized fullerenes. K values for the complexes of C60, C70, 1 and 2 with 3 are determined to be 6500, 22,230, 47,800 and 54,770 dm3 mol(-1), respectively. The magnitude of K suggests that 3 preferentially binds C70 and derivatized C70 in comparison to C60 and 1. Time resolved emission measurements establish that C(70)-3 and 2-3 complexes are stabilized much more in comparison to C(60)-3 and 1-3 systems in terms of charge separation process. Semi empirical calculations employing third parametric method substantiate the strong binding of C70 and its derivative with 3 in terms of heat of formation values of the respective complexes, and at the same time, determine the orientation of bound guest (here fullerenes) with the molecular plane of 3.     

Intracellular uptake and photodynamic activity of water-soluble [60]- and [70]fullerenes incorporated in liposomes

Water-soluble fullerenes have attracted attention as promising compounds that have been used to forge new paths in the field of photo-biochemistry. To prepare water-soluble fullerenes, we employed lipid-membrane-incorporated fullerenes (LMICx; x=60 or 70) by using the fullerene exchange method from a gamma-cyclodextrin (gamma-CD) cavity to vesicles. LMIC60 have low toxicity in the dark and engender cell death by photoirradiation (lambda>350 nm). Furthermore, the photodynamic activity of LMIC70 is 4.7-fold that of LMIC60 for the same photon flux (lambda>400 nm). One of the reasons for the higher phototoxicity of LMIC70 is the higher generation of singlet oxygen (1O2) in LMIC70 than in LMIC60. The difference between LMIC60 and LMIC70 is considered to be simply derived from the amount of light absorption in the 400-700 nm region that is suitable for photodynamic therapy (PDT). To the best of our knowledge, this is the first case in which biological activity of C70 and its derivatives toward HeLa cells has been assayed.     

Synthesis of large macrocyclic azacalix[n]pyridines (n = 6 - 9) and their complexation with fullerenes C(60) and C(70)

Large methylazacalix[n]pyridines (n = 6-9) were synthesized effectively from the Pd-catalyzed macrocyclic fragment coupling reactions between alpha,omega-dibrominated and alpha,omega-diaminated linear oligomers. As macrocyclic host molecules, they formed a 1:1 complex with fullerenes C(60) and C(70) with association constants ranging from 3 x 10(4) to 1 x 10(5) M(-1).     

Spectral and theoretical studies on effective and selective non-covalent interaction between tetrahexylporphyrins and fullerenes

The host-guest interaction of zinc(II) 5,10,15,20-tetrahexylporphyrin (Zn-THP) and its free base (H2-THP) with fullerenes (C60 and C70) has been studied in toluene medium. Binding constants (K) for H2- and Zn-THP complexes of fullerenes were determined by UV-vis, fluorescence and NMR spectroscopic techniques. Large K values of C70/THP complexes (KC70 ) were obtained in the range of 1.4-2.5 x 10(4)M(-1), while those of C60/THP complexes (KC60) were smaller (1.0-3.2 x10(3)M(-1)). These results show that the KC70 is about 10 times as large as KC60 in both THPs (KC70/KC60 = 10). Enthalpies of formation (DeltaHf degrees) for various fullerene/THP complexes were estimated by ab initio calculations; DeltaHf degrees for C60/H2-THP, C70/H2-THP, C60/Zn-THP and C70/Zn-THP complexes are 5.82, 2.80, 2.31 and 1.54 kcal mol(-1), respectively. The trends in DeltaHf degrees support the experimental results of selective complexation of THPs towards C70 over C60 and fullerenes towards Zn-THP over H2-THP.     

Synthesis and structure of nitrogen bridged calix[5]- and -[10]-pyridines and their complexation with fullerenes

Azacalix[5]pyridine, a heteroatom bridged calixaromatic with an odd number of arene units, and azacalix[10]pyridine, a giant molecular belt, were selectively synthesized based on a 2 + 3 macrocyclic coupling strategy; both novel macrocyclic hosts formed strong 1 : 1 complexes with fullerenes C60 and C70 in a size-selective manner with association constants up to 1.3 x 10(5) +/- 0.03 x 10(5) M(-1).     

Noncovalent endo-binding of fullerenes to diprotonated bisporphyrins

Noncovalent binding of fullerenes to bisporphyrins was studied in the gas phase by energy-dependent collision-induced dissociation (CID) with Xe under single-collision conditions. The electrospray ionization mass spectra of calix[4]arene-linked bisporphyrins show that bisporphyrins take up to 3-4 protons, depending on the type of meso-substituents. Of the protonated bisporphyrins, the diprotonated species form stable 1:1 complexes with fullerenes (C(60) and C(70)). CID cracking patterns of the diprotonated bisporphyrins indicate that each monomeric porphyrin moiety is singly protonated. CID yield-energy curves obtained from the 1:1 diprotonated bisporphyrin-fullerene complexes suggest that a fullerene occupies the endo-binding site intercalated between the two singly protonated porphyrin moieties. In the cases of 1:2 diprotonated bisporphyrin-fullerene complexes, CID results show that one fullerene binds inside (endo-binding) and the other outside (exo-binding). The exo-binding mode is energetically almost identical to the binding of fullerenes to singly protonated porphyrin monomers. The endo-binding energy is at least twice the exo-binding energy. To gain insights into the binding mode, we optimized structures of diprotonated bisporphyrins and their 1:1 endo-complexes with fullerenes, and calculated the endo-binding energy for C(60), C(70) (end-on), and C(70) (side-on). The endo-binding of fullerenes to diprotonated bisporphyrins nearly doubles the π-π interactions while reducing the electrostatic repulsion between the two singly protonated porphyrin moieties. The side-on binding of C(70) is favored over the end-on binding because the former exerts less steric strain to the lower rim of calixarene.     

Stabilities of multiply charged dimers and clusters of fullerenes

The authors find even-odd variations as functions of r (...+[C60]2(r+)([C60C70](r+)) electron-transfer collisions. This even-odd behavior is in sharp contrast to the smooth one for fullerene monomers and may be related to even-odd effects in dimer ionization energies in agreement with results from an electrostatic model. The kinetic energy releases for dimer dissociations [predominantly yielding intact fullerenes [C60]2(r+)-->C60(r1+)+C60(r2+) in the same (r1=r2) or nearby (r1=r2+/-1) charge states] are found to be low in comparison with the corresponding model results indicating that internal excitations of the separating (intact) fullerenes are important. Experimental appearance sizes for the heavier clusters of fullerenes [C60]n(r+) (n>3 and r=2-5) compare well with predictions from a new nearest-neighbor model assuming that r unit charges in [C60]n(r+) are localized to r C60 molecules such that the Coulomb energy of the system is minimized. The system is then taken to be stable if (i) two (singly) charged C60 are not nearest neighbors and (ii) the r C60(+) molecules have binding energies to their neutral nearest neighbors which are larger than the repulsive energies for the (r-1) C60(+)-C60(+) pairs. Essential ingredients in the nearest-neighbor model are cluster geometries and the present results on dimer stabilities.     

Stability of silicon-doped C60 dimers

A theoretical investigation on the structure, stability, and thermal behaviors of the smallest polymeric units, the dimers, formed from substitutionally Si-doped fullerenes is presented. A density functional based nonorthogonal tight-binding model has been employed for describing the interatomic interactions. The study focuses on those polymeric structures which involve Si-Si or Si-C interfullerene bonds. The binding energy of the dimers increases with their Si content from about 0.25 eV in C(60)-C(60) to about 4.5 eV in C(58)Si(2)-C(58)Si(2). Moreover, the C(59)SiC(59) dimer, linked through the sharing of the Si atom between the two fullerenes, has been also considered. Upon heating, the dimers eventually fragment into their constituent fullerene units. The fragmentation temperature correlates with the strength of the interfullerene bonds. C(58)Si(2)-C(58)Si(2) exhibits a higher thermal stability (fragmentation temperature of approximately 500 K) than the pure carbon C(60)-C(60) dimer (with a fragmentation temperature of approximately 325 K). Given the higher structural and thermal stabilities of the Si-doped fullerene dimers, the authors propose the use of substitutionally Si-doped fullerenes as the basic units for constructing new fullerene-based polymers.     

Determination of binding strength for the supramolecular complexation of a designed bisporphyrin with C60, C70 and their derivatives employing absorption spectrophotometric, fluorescence and quantum chemical calculations

The present paper reports the synthesis of a designed bisporphyrin (1), and its supramolecular complexes with C60, C70 and their derivatives, namely, tert-butyl-(1,2-methanofullerene)-61-carboxylate (2) and [6,6]-phenyl C70 butyric acid methyl ester (3) in toluene medium. C60, C70 and their derivatives undergo ground state non-covalent interaction with 1 is evidenced from absorption spectrophotometric study in which it is observed that the intensity of the Soret absorption band of 1 decreases considerably in presence of C60, C70 and their derivatives. Steady state fluorescence studies reveal efficient quenching of fluorescence of 1 in presence of fullerenes. The binding constant (K) values of the fullerene/1 complexes follows the trend: 2/1相似文献   

Supramolecular inclusion complexes of two cyclic zinc bisporphyrins with C60 and C70: structural, thermodynamic, and photophysical characterization

The formation of thermodynamically stable inclusion complexes between two cyclic zinc bisporphyrins, differing in the saturation degree of the hydrocarbon linkers that connect their porphyrin units, and the fullerenes C(60) and C(70) is described. Binding and photophysical studies were performed in two solvents of very different polarity: toluene and dichloromethane. UV/Vis and fluorescence titration experiments showed π-π interactions between the cyclic zinc bisporphyrins and the fullerenes. Solid-state structures were determined by X-ray diffraction analysis and gave valuable insight into the different complexation behaviors of the two macrocyclic systems towards the fullerenes. NMR titrations were also helpful in understanding the geometry of the complexes in solution. Upon fullerene complexation, the two macrocyclic bisporphyrins adopt very distinct conformations. Charge-transfer absorption bands point to ground-state interactions, and quenching of the porphyrin component luminescence indicates fast reactivity in the excited states. Energy transfer plus HOMO-HOMO and LUMO-LUMO electron-transfer processes occur within the complexes. Charge-separated states characterized by a reduced fullerene and an oxidized porphyrin radical, with lifetimes in the order of several hundred picoseconds, are detected.     

6,7‐Bismethoxy‐2,11‐dihydroxytetraphenylene Derived Macrocycles: Synthesis,Structures, and Complexation with Fullerenes

6,7‐Bismethoxy‐2,11‐dihydroxytetraphenylene ( 1 ), a novel building block of tetraphenylene‐derived macrocycles, was synthesized via palladium‐catalyzed cross‐coupling reactions and characterized by X‐ray diffraction. The relevant macrocyclic hosts derived from 1 have well‐defined structures with fixed conformations both in solution and solid state. They showed efficient and unique properties toward complexation with fullerenes C₆₀ and C₇₀ in toluene.     

Selective syntheses of novel polyether fullerene multiple adducts

We have applied a modified macrocyclic tether approach to control multiple additions to C60. The technique of 3He NMR was used to confirm the selective formation of specific C60 multiple adducts by the macrocyclic tether approach. An oligoglycol was used as a flexible linker to produce macrocyclic polyether-linked malonates 5, 6, 8, and 9 under solid-liquid PTC (phase-transfer-catalysis) conditions. The formation of a single C60 tris-adduct, 3, from macrocyclic malonate 1 and 3He@C60 was proven by 3He NMR. Similarly, multiple additions to C60 of macrocyclic polyether malonate 5 gave C60 bis-adduct 10 selectively, while the reaction of C60 with macrocyclic malonate 8 gave bis-adducts 11 and 12. A similar process with macrocyclic malonate 6 gave tris-adduct 13 with high selectivity as well. Saponification of these C60 multiple adducts gives the corresponding polyacids that are potentially useful in biological applications. Macrocyclic polyether fullerenes are a new class of ionophores, which could be interesting for molecular recognition and for the development of biosensors.     

富勒烯(C60／C70)与N，N，N’，N’-四-(对甲苯基)-4，4’-二胺-1，1’-二苯硒醚(TPDASe)间光诱导电子转移过程的激光光解研究

富勒烯(C60／C70)与N，N，N’，N’-四-(对甲苯基)-4，4’-二胺-1，1’-二 苯硒醚(TPDASe)间在激光光诱导条件下，发生了分子间的电子转移过程．在可见- 近红外区(600-1200nm)，观测到了TPDASe阳离子自由基、富勒烯(C60／C70)激发三 线态和阴离子自由基，在苯腈溶液中，观测瞬态谱测定了电子从TPDASe转移到富勒 烯(C60／C70)激发三线态的量子转化产率(Φet^T)和电子转移常数(Ket)．     

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.     

Self-assembly of C(60) pi-extended tetrathiafulvalene (exTTF) dyads on gold surfaces

The first self-assembly of a C60 pi-extended tetrathiafulvalene (exTTF) dyad on a gold surface is reported. Four fullerene derivatives, two of them containing p-quinonoid pi-extended tetrathiafulvalenes (exTTFs), have been synthesized, and their solution electrochemistry has been investigated by means of cyclic voltammetry. Fullerene-containing SAMs of thioctic acid derivatives 3 and 6 have also been investigated by cyclic voltammetry. The cyclic voltammograms of both compounds exhibit three reversible reduction waves, and for compound 6, one irreversible oxidation process corresponding to the oxidation of the exTTF subunit is observed. Stable self-assembled monolayers (SAMs) of fullerene derivative 3 were formed on gold surfaces, whereas dyad 6 does not present a very clear electrochemical response, most probably as a result of structural rearrangements on the monolayer or charge transfer between the C60 and exTTF moieties.     

First-principles study of hydrogen storage on Li12C60

Solid state materials capable of storing hydrogen with high gravimetric (9 wt %) and volumetric density (70 g/L) are critical for the success of a new hydrogen economy. In addition, an ideal storage system should be able to operate under ambient thermodynamic conditions and exhibit fast hydrogen sorption kinetics. No materials are known that meet all these requirements. While recent theoretical efforts showed some promise for transition-metal-coated carbon fullerenes, later studies demonstrated that these metal atoms prefer to cluster on the fullerene surface, thus reducing greatly the weight percentage of stored hydrogen. Using density functional theory we show that Li-coated fullerenes do not suffer from this constraint. In particular, we find that an isolated Li(12)C(60) cluster where Li atoms are capped onto the pentagonal faces of the fullerene not only is very stable but also can store up to 120 hydrogen atoms in molecular form with a binding energy of 0.075 eV/H(2). In addition, the structural integrity of Li(12)C(60) clusters is maintained when they are allowed to interact with each other. The lowest energy structure of the dimer is one where the Li atom capped on the five-member ring of one fullerene binds to the six-member ring of the other. The binding of hydrogen to the linking Li atom and the potential of materials composed of Li(12)C(60) building blocks for hydrogen storage are discussed.