A comparative study of molecular complexation of [60]- and [70]fullerenes with 1,3,5-tribromobenzene by UV-vis spectrophotometric method

By UV-vis spectrophotometric method it has been shown that 1,3,5-tribromobenzene (TBB) forms molecular complexes of 1:2 stoichiometry with [60]- and [70]fullerenes. An isosbestic point could be detected in case of the [70]fullerene complex. The formation constant of the [60]fullerene complex is higher than that of the [70]fullerene complex at each of the four temperatures under study. This is in opposite order of the electron affinities of the two fullerenes; moreover, no charge transfer band was observed in the spectra of either complex in solution. This indicates that van der Waals forces, rather than CT interactions, are responsible for complexation. The results reveal that the C-atoms at the pentagon vertices of [60]fullerene have greater polarizing power than those in [70]fullerene.     

Absorption spectrophotometric study of supramolecular complexation of [60]- and [70]fullerenes with 24,26-dimethoxy-25,27-dihydroxy calix[4]arene

Supramolecular interactions of 24,26-dimethoxy-25,27-dihydroxy calix[4]arene (1) with [60]- and [70]fullerenes have been studied in only chloroform and in a ternary solvent mixture comprising of chloroform, ethyl alcohol and toluene by UV-vis absorption spectrophotometric method. The experimental results are explained using the model that takes into account the interaction between electronic subsystems of 1 and fullerene. The most interesting feature is the preference of [60]fullerene over [70]fullerene for 1 in ternary solvent mixture as revealed by higher value of formation constant of [60]fullerene/1 complex. The selectivity towards [60]fullerene opens up the way toward self-assembling systems and new separation and purification methods for fullerenes.     

Spectroscopic and thermodynamic study of charge transfer interactions of retinol palmitate with [60]- and [70]fullerenes by absorption spectrometric method

Retinol palmitate (1), which is commonly called "Vitamin A palmitate", has been shown to form charge transfer (CT) complexes with a series of electron acceptors including [60]- and [70]fullerenes, and from the trends in CT transition energies the vertical ionization potential of 1 has been estimated to be 7.73eV. Stoichiometries of the fullerene complexes have been shown to be 1(Vitamin 1): 1([70]fullerene) and 1(Vitamin 1): 2([60]fullerene). The enthalpies and entropies of formation of these two complexes have been determined by estimating the formation constants spectrophotometrically at five different temperatures. The complexation phenomenon may be utilised to dissolve the fullerenes in the non-toxic Vitamin A oil and the solution may be used for testing the biological activity of the fullerenes in vivo.     

Spectrophotometric study of the supramolecular complexes of [60]- and [70]Fullerenes with biscalix[6]arene and crown[4]calix[6]arene

[60]- and [70]Fullerenes have been shown to form 1:1 supramolecular complexes with bis[2-(5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41-pentahydroxycalix[6]arenyl-oxy ethyl ether) (1) and 5,11,17,23,29,35-hexa-tert-butyl-37,38,40,41-tetra hydroxyl-39,42-(crown-4)calix[6]arene (2) in CHCl3 medium by electronic absorption spectroscopy. Formation constants (K) of the complexes of [60]- and [70]fullerenes with 1 and 2 have been determined at room temperature from which free energy of formation values of the complexes have been estimated. The very high formation constant value of [60]fullerene/1 complex (5900 dm3 mol-1) in indicative of formation of inclusion complex. Moreover, PM3 calculations reveal that intermolecular interaction between [60]fullerene and 1 proceeds through quite deep energy molecular orbital.     

Charge Transfer in the Electron Donor-Acceptor Complexes of [60]Fullerene/PM567 and [70]Fullerene/PM567

UV-Vis spectroscopic investigations of electron donor-acceptor complexes of [60]- and [70]fullerenes with a well-known laser dye, viz., 4,4-difluoro-1,3,5,7,8-pentamethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indecene (PM567), are reported in toluene solutions. Absorption bands due to charge transfer (CT) transitions have been located in the visible region. The vertical ionization potential of PM567 has been determined utilizing Mulliken’s equation. A possible mechanism for the interaction between the electronic subsystems of [60]- and [70]fullerenes with PM567 is discussed. Oscillator strengths, resonance energies and electronic coupling elements of the CT complexes were estimated. Formation constant data and ab initio calculations suggest that PM567 binds more tightly with [60]fullerene compared to [70]fullerene.     

NMR spectrometric study of molecular complex formation of [60]- and [70]fullerenes with a number of phosphine oxides

Molecular complex formation between [60]- and [70]fullerenes with a series of phosphine oxides, namely, tri-n-octyl phosphine oxide, triphenyl phosphine oxide and tri-n-butyl phosphine oxide has been studied in CCl4 medium by NMR spectrometric method. Both [60]- and [70]fullerenes have been shown to form 1:1 adducts with the above series of phosphine oxides. Formation constants (K) for all the complexes have been determined from the systematic variation of NMR chemical shifts of specific protons of the donors in presence of [60]- and [70]fullerenes. Trends in the values of K suggest that [70]fullerene binds stronger with the phosphine oxides relative to [60]fullerene.     

Energies of Charge Transfer for the Supramolecular Complexes of [60]- and [70]Fullerenes with a Series of meso-Tetraphenylporphyrins in the Solution State

Supramolecular complexes of [60]- and [70]fullerenes with various meso-tetraphenylporphyrins in toluene solutions have been studied by electronic absorption spectroscopy. Charge transfer (CT) absorption bands are observed in the visible region. Vertical ionization potentials (I _D ^V) of the meso-tetraphenylporphyrins are reported from a study of EDA interaction of these porphyrins with a number of electron acceptors like o-chloranil, p-chloranil, 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and vitamin K. The dependence of the CT transition energy on the donor ionization potential has been utilized to estimate the vertical electron affinities (E _A ^V) of [60]- and [70]fullerenes in solution. The value of E _A ^V for [60]fullerene is found to be 0.10 eV lower in magnitude than that of [70]fullerene. We have extracted degrees of CT, and oscillator and transition dipole strengths of the fullerenes/meso-tetraphenylporphyrins complexes. The experimental results show that the CT complexes studied here have a neutral character in their ground states. Electronic coupling elements have been determined for fullerene/meso-tetraphenylporphyrin complexes. Values of the solvent reorganization energy indicate that the electron transfer process takes place at a faster rate in the case of [70]fullerene/meso-tetraphenylporphyrin complexes.     

NMR spectrometric studies of complexation of [60]fullerene with series of meso-tetraphenylporphyrins

Extensive 1H NMR spectrometric studies have been done to gain information on the nature of molecular interactions of the supramolecular complexes of [60]fullerene with a series of meso-tetraphenylporphyrins, namely, meso-5,10,15,20-tetraphenylporphyrin (1), meso-5,10,15,20-tetra-2-bromophenyl-porphyrin (2) and meso-5,10,15,20-tetra-2-chlorophenyl-porphyrin (3) in toluene medium. [60]Fullerene has been shown to form 1:1 adducts with the above series of meso-tetraphenylporphyrins. Formation constants (K) for all the complexes have been determined from the systematic variation of the NMR chemical shifts of beta proton of the porphyrin in presence of [60]fullerene. It has been observed that 3 acts as a better donor in forming supramolecular complex with [60]fullerene.     

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.     

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   

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.     

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.     

Solution NMR studies of supramolecular complexes of [60]- and [70]fullerenes with mono O-substituted calix[6]arene

Supramolecular complexation of [60]- and [70]fullerenes with 37-allyl-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert butyl)calix[6]arene (I) has been studied in CCl(4) medium by NMR spectrometric method. All of the complexes are found to be stable with 1:1 stoichiometry. Formation constants (K) of the above supramolecular complexes have been determined from systematic variation of NMR chemical shifts of specific protons of I in the presence of [60]- and [70]fullerenes. Trends in the K value suggest that [70]fullerene binds more strongly with I relative to [60]fullerene. Both PM3 and ab initio calculations reveal that the intermolecular interaction in the [70]fullerene/I complex proceeds through quite deep energy minima.     

Interaction between bisphenol A and tannic acid: spectroscopic titration approach

The present paper reports the photophysical investigations of a designed bisporphyrin (1), and its supramolecular complexes with C60 and C70 in toluene medium. UV-vis studies reveal appreciable ground state interaction between fullerenes and 1. The stoichiometry of the fullerene complexes of 1 is found to be 1:1. Steady state fluorescence studies elicit quenching of fluorescence of 1 in the presence of fullerenes. The binding constants of the C60/1 and C70/1 complexes are estimated to be 3760 and 31,222.5 dm3 mol(-1), respectively. Time resolved emission studies establish relatively long-lived charge separated state for the C70/1 complex. Molecular mechanics calculations in vacuo evoke the stereoscopic structures of the fullerene/1 complexes and interpret the stability difference between C60 and C70 complexes of 1 in terms of heat of formation values.     

Water-soluble fullerenes using solubilizing agents, and their applications

Host–guest and supramolecular chemistry can produce water-solubilization of fullerenes such as C₆₀, C₇₀, and C_60/70 derivatives by hydrophobic interactions, CH–π interactions, and/or π–π interactions. For materials and biomedical applications, these water-soluble host–fullerene complexes must have the following important properties: (i) high solubility, (ii) high stability, and (iii) functionalization of the host–fullerene complex. These objectives can be achieved by selection of appropriate host molecules, development of novel solubilizing methods, and synthesis of functionalized host molecules. This review describes the introduction of a variety of host molecules that can solubilize fullerenes in water. In addition, we describe applications of host–fullerene complexes, in particular using photoinduced energy- and electron-transfer processes in water.     

Spectrophotometric and thermodynamic studies of [60]fullerene/methylbenzene charge transfer complexes

The absorption spectra of charge-transfer (CT) complexes of [60]fullerene with liquid methylbenzenes, viz. toluene, o-xylene, m-xylene, p-xylene and mesitylene have been investigated in CCl(4) medium. An absorption band due to CT transition is observed in each case in the visible region. The experimental CT transition energies are well correlated (through Mulliken's equation) with the ionisation potentials (I(D)) of the series of methylbenzenes studied. From an analysis of this variation the electron affinity of [60]fullerene has been found to be 2.32 eV. The degrees of charge transfer in the ground state of the complexes have been found to be very low (0.66-0.775%). It has been found that these methylbenzenes form stable 1:1 complexes with [60]fullerene. Formation constants of the complexes have been determined at four different temperatures from which the enthalpies and entropies of formation of the complexes have been obtained. The experimentally determined formation constants of the complexes of [60]fullerene with methylbenzenes exhibit a very good linear free energy relationship (Chem. Rev. 53 (1953) 191).     

Spectroscopic and Theoretical Investigations on Supramolecular Interaction of a Newly Designed Monoporphyrin with Fullerenes and Functionalized Fullerenes in Solution

The present paper reports the results of a photophysical investigation of a designed monoporphyrin (1) and its supramolecular complexes with C₆₀, C₇₀ and derivatized fullerenes, namely tert-butyl-(1,2-methanofullerene)-61-carboxylate (2) and [6,6]-phenyl C₇₁ butyric acid methyl ester (3) in toluene. UV–vis studies reveal appreciable ground state interaction between the fullerenes and compound 1. Steady state fluorescence studies show quenching of fluorescence of 1 in the presence of fullerenes. The binding constants of the C₆₀/1, C₇₀/1, 2/1 and 3/1 complexes are estimated to be 300, 20770, 1150 and 13170 dm³⋅mol⁻¹, respectively. Molecular mechanics calculations in vacuo evoke the stereoscopic structures of the fullerene/1 complexes and allow interpretation of the stability difference among various fullerene complexes of 1 in terms of their enthalpies of formation.     

Regioselective synthesis of tetra(aryl)-mono(silylmethyl)[60]fullerenes and derivatization to methanofullerene compound

A method for the facile synthesis of tetraaryl-trimethylsilylmethyl-hydro[60]fullerenes, C₆₀Ar₄(CH₂SiMeR)H, has been developed in which readily prepared anionic mono(silylmethyl) fullerene is subjected to reaction conditions for organocopper-mediated multiple addition. Penta(organo)fullerene derivatives bearing different substituents and diverse functionality were synthesized in moderate to good yield under simple and mild reaction conditions. Further organic and organometallic transformations of these fullerenes allowed us to synthesize transition-metal complexes and a new methanofullerene derivative, 1,9-methano-6,12,15,18-tetraphenyl[60]fullerene, C₆₀Ph₄(CH₂).     

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.     

Manganese(III) acetate-mediated free radical reactions of [60]fullerene with beta-dicarbonyl compounds

[60]Fullerene reacted with various beta-dicarbonyl compounds in the presence of Mn(OAc)3*2H2O to generate dihydrofuran-fused [60]fullerene derivatives or 1,4-bisadducts. Dihydrofuran-fused [60]fullerene derivatives 2 could be formed by treatment of alpha-unsubstituted beta-diketones 1a-e or beta-ketoesters 1f and 1g with [60]fullerene in refluxing chlorobenzene in the presence of Mn(III). Solvent-participated unsymmetrical 1,4-bisadducts 3 were obtained through the reaction of [60]fullerene with dimethyl malonate 1h or alpha-substituted beta-dicarbonyl compounds 1i-1n in toluene. A possible reaction mechanism for the formation of different fullerene derivatives is proposed.