Spectrophotometric studies of complexation of [60]fullerene with series of aromatic hydrocarbon molecules containing flexible phenyl substituents

The absorption spectra of the electron donor-acceptor complexes of [60]fullerene with five different aromatic hydrocarbon (AH) molecules containing flexible phenyl substituents have been investigated in toluene medium. An absorption band due to charge transfer (CT) transition is observed in each case in the visible region. The experimental CT transition energies are well correlated with the vertical ionization potentials of the AHs studied (through Mulliken's equation) from which we extract degrees of charge transfer, oscillator and transition dipole strengths of the CT complexes. The degrees of CT in the ground state of the complexes have been found to be very low (0.49-0.55%). The formation constants (K) for the complexes of [60]fullerene with the aromatic hydrocarbons have been determined by UV-vis spectroscopy. Both K values and PM3 calculations on [60]fullerene/AH complexes reveal that nature of substitution in the donor moiety as well as steric compatibility with the acceptor molecule govern the process of EDA complex formation.     

Study of charge transfer complexes of [70]fullerene with phenol and substituted phenols

To improve the understanding of the charge transfer (CT) interaction of [70]fullerene with electron donors, interaction of [70]fullerene with a series of phenols, e.g., phenol, resorcinol and p-quinol were studied in 1,4-dioxan medium using absorption spectroscopy. An absorption band due to CT transition was observed in the visible region. The experimental CT transition energies (h nuCT) are well correlated (through Mulliken's equation) with the vertical ionisation potentials (I(D)v) of the series of phenols studied. From an analysis of this correlation degrees of charge transfer for the [70]fullerene-phenol complexes were estimated. The degrees of charge transfer in the ground state of the complexes have been found to be very low (<2%). The h nuCT values change systematically as the number and position of the -OH groups change on the aromatic ring of the phenol moiety. From the trends in the h nuCT values, the Hückel parameters (h(O) and k(C-O)) for the -OH group were obtained in a straightforward way and the values so obtained, viz., 1.91 and 1.0, respectively, are close to the ones (1.8 and 0.8) recommended by Streitwieser on the basis of other evidence. Oscillator strengths, transition dipole strengths and resonance energies of the [70]fullerene-phenol complexes were determined. Formation constants of the CT complexes were determined at four different temperatures from which enthalpies and entropies of formation of the complexes were estimated.     

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.     

Energies of charge transfer and formation equilibria of the complexes of [70]fullerene with some interesting polyaromatic molecules

We have investigated electron donor-acceptor complexes of [70]fullerene with various polyaromatic molecules (PAM) with different vertical ionization potentials (I(D)(v)). Well defined charge transfer (CT) absorption bands have been located in the visible region. We extract degrees of charge transfer, oscillator and transition dipole strengths by analyzing the transition energy of the CT band as a function of I(D)(v) of the donors studied. The experimental results were explained using a theoretical model that takes into account the interaction between electronic subsystems of PAM with [70]fullerene. Trends in the formation constant for the [70]fullerene/PAM complexes were discussed in terms of enthalpies and entropies of formation.     

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).     

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.     

Study of the formation equilibria of electron donor-acceptor complexes between [60]fullerene and methylbenzenes by absorption spectrometric method.

The electron donor-acceptor (EDA) interaction between [60]fullerene and three methylbenzenes, viz., durene, pentamethylbenzene and hexamethylbenzene has been studied in carbon tetrachloride medium at a number of temperatures. It has been found that these methylbenzenes form stable 1:1 EDA complexes with [60]fullerene. Charge transfer (CT) absorption bands of the complexes in the 410-460 nm region are more intense than the usual 420-700 nm absorption band of C60. The CT transition energies (hvCT) of the complexes change systematically with change in the number and position of the methyl groups in the donor molecules (methylbenzenes) and also with the donor ionisation potentials. From an analysis of this variation the electron affinity of C60 has been found to be 2.30 eV and also an inductive effect Hückel parameter of the methyl group has been determined. Formation constants (K) have been determined at three different temperatures from which the enthalpies and entropies of formation of the complexes have been determined.     

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.     

Energies of charge transfer and supramolecular interactions of some mono O-substituted calix[6]arenes with [60]fullerene by absorption spectrometric method

Equilibria for the formation of supramolecular complexes of [60]fullerene with a series of mono O-substituted calix[6]arenes, namely: (i) 37-methoxy-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (1), (ii) 37-allyl-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (2), (iii) 37-phenacyl-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (3), (iv) 37-ethylester-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (4) and (v) 37-benzyl-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (5) have been studied in CCl4 medium by absorption spectroscopic technique. The stoichiometry has been found to be 1:1 ([60]fullerene:calix[6]arene) in each case. An absorption band due to charge transfer (CT) transition is observed in each case in the visible region. The vertical ionisation potentials (I(D)(v)) of all the calix[6]arenes under study have been estimated utilising CT transition energy. The experimental I(D)(v) values also yield a good estimate of the electron affinity of [60]fullerene. The degrees of CT in the ground state of the complexes have been found to be very low (about 0.15%). Resonance energy of the complexes have been estimated. Thermodynamic parameters for the supramolecular complex formation of [60]fullerene with mono O-substituted calix[6]arene receptors are reported. It is observed that among the calix[6]arenes under the present study, only 1 and 4 form inclusion complexes with [60]fullerene. This has also been substantiated by theoretical calculation using PM3 method. Thus presence of one substituent group (of different types) on the lower rim of the calix[6]arene molecule has been shown to govern the host-guest complexation process.     

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.     

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.     

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.     

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.     

Study of ground state EDA complex formation between [70]fullerene and a series of polynuclear aromatic hydrocarbons.

[70]fullerene has been shown to form 1:1 EDA complex with anthracene, naphthalene, phenanthrene, pyrene and acenaphthene in CCl4 medium. Charge transfer (CT) bands have been detected in all the cases. Isosbestic points have been observed in the cases of phenanthrene and acenaphthene complexes. Ionisation potentials of the donors and CT transition energies have been found to correlate in accordance with Mulliken equation and from this correlation the electron affinity of C70 has been found to be 2.59 eV. Enthalpies and entropies of formation of the complexes have been estimated from the formation constants of the complexes determined spectrophotometrically at three different temperatures.     

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.     

Supramolecular interactions of [60]- and [70]fullerenes with calix[n]arenes

[60]- and [70]fullerenes have been shown to form 1:1 supramolecular complexes with (i) 24,26-dimethoxy-25,27-dihydroxy-5,11,17,23-tetra(4-tert-butyl)calix[4]arene (1) and (ii) 37,39,41-trimethoxy-38,40,42-trihydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (2) in CCl(4) medium by absorption spectroscopy. Charge transfer absorption bands of the complexes have been located in each of the cases (except [70]fullerene-2 complex) studied from which the vertical ionisation potential of 1 has been obtained. 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. Moreover, the formation constant of [70]fullerene-2 complex is higher than that of the [60]fullerene-1 and [60]fullerene-2 complexes at all the four temperatures studied. This has been accounted in terms of greater cavity size of 2 which is a calix[6]arene compared to 1 which is a calix[4]arene and also by the fact that a high degree of preorganisation takes place in case of 2 through intramolecular H-bonding at its lower rim.     

Absorption spectrometric study of molecular complex formation between [60]fullerene and a series of methylated pyridines

[60]fullerene has been shown to form 1:1 molecular complexes with pyridine and some methylated pyridines such as 2-picoline, 3-picoline, 4-picoline, 2,6-lutidine and 2,4,6-collidine in CCl4 medium by absorption spectrometric method. Well defined charge transfer (CT) bands have been observed for complexes of C60 with all the pyridines studied except 4-picoline. From an analysis of the trends in the CT absorption bands the ionisation potentials of the methylpyridines have been determined. The electron affinity of C60 has also been determined from the spectral data. The formation constants of the complexes exhibit a very good linear free energy relationship from which the Hammett p parameter for the complexation process is found to be -2.96.     

NMR spectrometric studies of complexation of [60]fullerene with series of anisoles

Detailed (1)H and (13)C NMR spectrometric studies have been carried out to gain insight into the nature of molecular interactions of the electron donor-acceptor (EDA) complexes of [60]fullerene with a series of anisoles, namely, anisole, m-bromoanisole, and p-bromoanisole. [60]Fullerene has been shown to form 1:1 adducts with the above series of anisoles. Formation constants (K) for all the complexes have been determined from the systematic variation of the NMR chemical shifts of specific protons of the anisoles in the presence of [60]fullerene. The K values of [60]fullerene/anisole, [60]fullerene/m-bromoanisole, and [60]fullerene/ p-bromoanisole complexes yield good estimates of the Hammett rho constant for the complexation reaction. To the best of our knowledge, this paper reports for the first time a very fruitful technique by which the concentrations of EDA complexes can be estimated from systematic variations of the (13)C NMR signal.     

Electrochemistry and [60]fullerene displacement reactions of (dihapto-[60]fullerene) pentacarbonyl metal(0) (M = Cr, Mo, W)

Cyclic voltammetry (CV) measurements on (eta(2)-C(60))M(CO)(5) complexes (M = Cr, Mo, W) in dichloromethane show three [60]fullerene-centered and reversible reduction/oxidation waves. The E(1/2) values of these waves are shifted to positive values relative to the corresponding values of the uncoordinated [60]fullerene in the same solvent. A Jahn-Teller type distortion of the spherical surface of [60]fullerene promoted by [60]fullerene-metal pi-backbonding may explain the observed positive shifts. Lewis bases (L = piperidine and triphenyl phosphine) displace [60]fullerene from (eta(2)-C(60))M(CO)(5) complexes. Analysis of the activation parameters for the metal-[60]fullerene dissociation, the metal-[60]fullerene bond enthalpies (from DFT computations), and metal-solvent (benzene) bond enthalpies (from DFT computations) suggests appreciable solvent contribution to the transition state leading to formation of the intermediate species solvent-M(CO)(5). Appreciable transition state stabilization due to solvation of the intermediate species is inferred for M = Mo and W. For M = Cr, stabilization of the intermediate species due to solvation is not accompanied by the corresponding transition state stabilization.     

以C70衍生物为电子受体的高效聚合物固体薄膜太阳能电池

以PC[70]BM(phenyl C71-butyric acid methyl ester)取代PC[60]BM(phenyl C61-butyric acid methyl ester)作为电子受体材料,以MEH-PPV(poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene])为电子给体材料,制成了本体异质结(bulk heterojunction,BHJ)聚合物太阳能电池.MEH-PPV/PC[70]BM器件在AM1.5G(80 mW/cm2)模拟太阳光的光照条件下得到了3.42%的能量转换效率,短路电流值达到了6.07 mA/cm2,开路电压0.85 V,填充因子为53%.通过紫外可见吸收光谱和外量子效率的研究,发现PC[70]BM作为电子受体,对扩大光谱的吸收范围和增加活性层的吸收系数有明显的作用.同时比较了不同溶剂对该体系器件性能的影响.通过原子力显微镜(AFM)、光暗导I-V曲线等研究,分析了1,2-二氯苯有利于给体相和受体相的微相分离和载流子的传输的原因.