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.     

Photophysical and theoretical investigations on fullerene/phthalocyanine supramolecular complexes

The present paper reports the photophysical aspects of a very interesting and unique host-guest interaction between fullerene and phthalocyanines, viz., free base phthalocyanine (H2-Pc) and zinc-phthalocyanine (Zn-Pc), in toluene medium. Ground state electronic interaction between these two supramolecules has been evidenced from the observation of well-defined charge transfer (CT) absorption bands in the visible region. Vertical ionization potentials of the phthalocyanines have been determined utilizing CT transition energy. Magnitude of degrees of CT reveals that, in the ground state, 2-4% CT takes place. Binding constants (K) for the fullerene/phthalocyanine complexes were determined from the fluorescence quenching experiment. Large K values in the ranges approximately 4.7 x 10(4) to 7.3 x 10(4) and 2.3 x 10(4) to 2.5 x 10(4) dm(3) x mol(-1) were obtained for the 1:1 fullerene complexes of Zn and H 2-Pc, respectively. Values of K suggest that both H 2- and Zn-Pc could not serve as an efficient discriminators between C60 and C70. Theoretical calculations as well as (13)C NMR studies establish that the orientation of C 70 toward phthalocyanine is favored in end-on orientation, which proves that interaction between fullerenes and phthalocyanines were governed by the electrostatic mechanism rather than dispersive forces associated with pi-pi interaction.     

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).     

Absorption spectrometric study of charge transfer complex formation between 4-acetamidophenol (paracetamol) and a series of quinones including vitamin K3

The formation of charge transfer (CT) complexes of 4-acetamidophenol (commonly called 'paracetamol') and a series of quinones (including Vitamin K3) has been studied spectrophotometrically in ethanol medium. The vertical ionisation potential of paracetamol and the degrees of charge transfer of the complexes in their ground state has been estimated from the trends in the charge transfer bands. The oscillator and transition dipole strengths of the complexes have been determined from the CT absorption spectra at 298 K. The complexes have been found by Job's method of continuous variation to have the uncommon 2:1 (paracetamol:quinone) stoichiometry in each case. The enthalpies and entropies of formation of the complexes have been obtained by determining their formation constants at five different temperatures.     

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.     

Vertical ionisation potentials of a number of crown ethers from charge transfer bands of their EDA complexes

Vertical ionisation potentials (I(v)D) of a number of crown ethers, viz. dibenzo-30-crown-10 (Crown 1), benzo-15-crown-5 (Crown 2), dibenzo-24-crown-8 (Crown 3), dicyclohexano-24-crown-8 (Crown 4) and 4'-nitrobenzo-15-crown-5 (Crown 5) are being reported for the first time from a study of EDA interaction of these crown ethers with a number of electron acceptors like C60, C70, o-chloranil, p-chloranil, 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and pyromellitic diimide (PMD). The study has been carried out in CCl4 medium by electronic absorption spectroscopy. Charge transfer (CT) absorption bands in the 360-900 nm range have been found in each case (excepting the 60 fullerene-Crown 4 system). The vertical ionisation potentials (I(v)D) of all the crown ethers thus determined show a good correlation with those calculated by the semiempirical AM1 method. Of the six acceptors under study the vertical electron affinity of PMD was not found in the literature. This has also been determined from an analysis of the present h(nu)(CT) data.     

Thermodynamics of coordination of pyridine and its substituted derivatives to osmium tetroxide

Complexation of osmium tetroxide (OsO₄) with pyridine and its substituted derivatives (i.e. 4-picoline, 3 -picoline, 4-tertbutylpyridine, methyl nicotinate, 3,4-dimethylpyridine, 3-chloropyridine, and 3-phenylpyridine) has been studied at different temperatures in benzene. Spectrophotometric measurements have been carried out to obtain the equilibrium constants and thermodynamic parameters. The equilibrium constants of the resulting 1:1 complexes are found to vary in the order 3,4-Me₂Py > 4-^tBuPy > 4-MePy > 3-MePy > Py > 3- PhPy > 3-C(O)OMePy ≈ 3-ClPy. All complexes are enthalpy stabilized whereas the entropy changes counteract the complexation. The results are discussed in terms of different basicities of the substituted pyridines.     

Study of electron donor-acceptor complexes of tri-n-octyl amine with [60]- and [70]fullerenes and some other electron acceptors by absorption spectrophotometric method

Electron donor-acceptor (EDA) complexes of tri-n-octylamine (TOA) with [60]- and [70]fullerenes and some other electron acceptors have been studied in chloroform medium by absorption spectrophotometric technique. Charge transfer (CT) absorption bands are observed in the visible region. Vertical ionization potential of TOA was determined utilizing CT transition energy. Oscillator strengths, transition dipole strengths and resonance energies for all the complexes have been calculated. [60]Fullerene/TOA and [70]fullerene/TOA complexes are found to decay slowly with time. Kinetics of these reactions have been studied and activation energies for such processes have been estimated. Ab initio calculations suggest that complexation of [70]fullerene with TOA is enthalpy favoured.     

A differential scanning calorimetry study of picoline complexes of cadmium chloride

The decomposition of picoline complexes of cadmium chloride has been studied using differential scanning calorimetry. The 2:1 complexes with 3-picoline and 4-picoline decompose in three steps corresponding to the loss of one, one-third, and two-thirds of a molecule of ligand, respectively, in these steps. Sample size apparently controls the mode of decomposition of the 1:1 complex with 2-picoline. In some cases, two-thirds of a molecule of ligands is lost and in other cases one-third is lost first. Thermal parameters have been determined for the various decomposition reactions.     

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.     

New photophysical insights in noncovalent interaction between fulleropyrrolidine and a series of zincphthalocyanines

The present article reports, for the first time, the photophysical aspects of noncovalent interaction of a fullerene derivative, namely, C(60) pyrrolidine tris-acid ethyl ester (PyC(60)) with a series of zincphthalocyanines, for example, underivatized zincphthalocyanine (1), zinc-1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (2), and zinc-2,3,9,10,16,17,23,24-octakis-(octyloxy)-29H,31H-phthalocyanine (3) in toluene. Ground state electronic interaction of PyC(60) with 1, 2 and 3 has been evidenced from the observation of well-defined charge transfer (CT) absorption bands in the visible region. Utilizing the CT transition energy, vertical electron affinity (E(A)(v)) of PyC(60) is determined. Steady state fluorescence experiment enables us to determine the value of binding constant (K) in the magnitude of 2.60 × 10(4) dm(3)·mol(-1), 2.20 × 10(4) dm(3)·mol(-1), and 1.27 × 10(4) dm(3)·mol(-1) for the noncovalent complexes of PyC(60) with 1, 2, and 3, respectively. K values of PyC(60)-ZnPc complexes suggest that PyC(60) is incapable of discriminating between 1, 2, and 3 in solution. Lifetime experiment signifies the importance of static quenching phenomenon for our presently investigated supramolecules and it yields larger magnitude of charge separated rate constant for the PyC(60)-1 species in toluene. Photoinduced energy transfer between PyC(60) and ZnPc derivatives, namely, 1, 2, and 3, in toluene, has been evidenced with nanosecond laser photolysis method by observing the transient absorption bands in the visible region; transient absorption studies establish that energy transfer from (T)PyC(60)* to the ZnPc occurs predominantly, as confirmed by the consecutive appearance of the triplet states of PyC(60). Theoretical calculations at semiempirical level (PM3) evoke the single projection geometric structures for the PyC(60)-ZnPc systems in vacuo, which also proves that interaction between PyC(60) and ZnPc is governed by the electrostatic mechanism rather than dispersive forces associated with π-π interaction.     

Structural, photophysical, and catalytic properties of Au(I) complexes with 4-substituted pyridines

Ionic gold(I) complexes with general formula of [Au(Py)2][AuCl2] and [Au(Py)2][PF6] (Py = 4-substituted pyridines) have been synthesized. Structures of five Au(I) complexes and a Ag(I) complex were determined by single crystal X-ray diffraction. Evidence for cationic aggregation of [Au(py)2][PF6] complexes in solution was obtained by conductivity measurements and by the isosbestic point observed from variable temperature UV-visible absorption spectra. All compounds were luminous in the solid state. Calculations employing density functional theory were performed to shed light on the nature of the electronic transitions. While the [Au(4-dmapy)2][AuCl2] (4-dmapy = 4-dimethylaminopyridine) and [Au(4-pic)2][AuCl2] (4-pic = 4-picoline) emissions were found to be mainly ligand in nature, their [PF6](-) counterparts involved a Au...Au-interaction imbedded in the highest occupied molecular orbital. [Au(4-dmapy)2][AuCl2] was found to be an efficient catalyst for Suzuki cross-coupling of aryl bromide and phenylboronic acid.     

Spectroscopic and thermodynamic study of charge transfer complexes of cloxacillin sodium in aqueous ethanol medium

Cloxacillin sodium has been shown to form charge transfer (CT) complexes of 1:1 stoichiometry with a number of electron acceptors in 50% (v/v) aqueous ethanol medium. From the trends in the CT absorption bands, the vertical ionization potential of the drug molecule (cloxacillin sodium) has been estimated to be 7.89 eV. The enthalpies and entropies of formation of two such complexes have been determined by estimating the formation constants spectrophotometrically at five different temperatures. The oscillator strengths and transition dipole moments of these complexes have been determined. It has further been noted that the reduction of o-chloranil by aqueous ethanol is completely inhibited by cloxacillin sodium, a phenomenon that makes the present study of formation equilibrium possible.     

Chemical Studies on Tobacco Smoke. LXI. Volatile Pyridines: Quantitative Analysis in Mainstream and Sidestream Smoke of Cigarettes and Cigars

Abstract

A quantitative analytical method has been developed for volatile pyridines in tobacco smoke using pyridine- ¹⁴C as an internal standard. Mainstream and sidestream smoke are trapped in 0.05 N sulfuric acid anti partitioned with chloroform. The acidic portion is then concentrated, adjusted to pH 3 and extracted with chloroform. Methanol and a trace of 2N sulfuric acid are added to this chloroform portion and the mixture is carefully concentrated.

A trace of sodium hydroxide is added and the final concentrate is analyzed by gas chromatography. Twenty-one volatile pyridines have been identified. The mainstream stroke of a popular. 85-mm U.S. cigarette without filter tip contained the following major pyridines: 33.4 μg pyridine, 12.3 μg α-picoline, 24.2 μg. β+γ-picoline, 7.6 μg 3-ethylpgridine, 5.9 μg: 4-ethylpyridine, and 23.3 μg 3,4-lutidine + 3-vinylpyridine. The sidestream smoke of this cigarette contained up to 28 times higher concentrations of pyridines.

Volatile pyridines were also determined in the mainstream smoke of other non-filter cigarettes, filter cigarettes, little cigars and, a non-tobacco cigarette. Of special interest were the much greater quantities of volatile pyridines in the mainstream and sidestream of cigars in comparison to those of cigarettes. The ratio of pyridines in sidestream to those in mainstream was 5 to 50 in large cigars. Selective filtration was observed with both cellulose acetate and charcoal filter tips. The analytical method resulted in reproducible values for pyridine, with an average recovery rate of more than 90%. In addition to pyridines, two pyrazines were also isolated from the smoke. Processed tobacco contained minute amounts of some volatile pyridines.     

Spectrophotometric study of the charge transfer complexation of some porphyrin derivatives as electron donors with tetracyanoethylene

Charge transfer complexes (CTC) of 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetra(4-tolyl)porphyrin (TTP), 5,10,15,20-tetra(4-methoxyphenyl)porphyrin (TMP), Zn-5,10,15,20-tetraphenylporphyrin (Zn-TPP), and Zn-5,10,15,20-tetra(4-tolyl)porphyrin (Zn-TTP) with tetracyanoethylene (TCNE) have been studied at various temperatures in CH(2)Cl(2) and CCl(4). The data are discussed in terms of equilibrium constant (K(CT)), molar extinction coefficient (varepsilon(CT)), thermodynamic standard reaction quantities (DeltaG degrees , DeltaH degrees and DeltaS degrees ), oscillator strength (f), and transition dipole moment (mu). The spectrum obtained for TPP/TCNE, TTP/TCNE, and TMP/TCNE systems shows two main absorption bands at 475 and 690nm, which are not due to the absorption of any of the reactants. These bands are characteristic of an intermolecular charge transfer involving the overlap of the lowest unoccupied molecular orbital (LUMO) of the acceptor with the highest occupied molecular orbital (HOMO) of the donor. The results reveal that the interaction between the donors and acceptor is due to pi-pi(*) transitions by the formation of radical ion pairs. The stoichiometry of the complexes was found to be 1:1 ratio by the Job and straight line methods between donors and acceptor with the maximum absorption bands at wavelengths of 475 and 690nm. The observed data show salvation effects on the spectral and thermodynamics properties of CTC. The ionization potential of the donors and the dissociation energy of the CTC were also determined and are found to be constant.     

Stepwise charge transfer complexation of some pyrimidines with sigma-acceptor iodine involving a new unconventional acceptor

Interactions of some pyrimidine derivatives, 4-amino-2,6-dimethylpyrimidine, kyanmethin, (4AP), 2-amino-4,6-dimethylpyrimidine (2AP), 2-aminopyrimidine (AP), 2-amino-4-methylpyrimidine (AMP), 2-amino-4-methoxy-6-methylpyrimidine (AMMP), and 4-amino-5-chloro-2,6-dimethylpyrimidine (ACDP) as electron donors, with iodine (I(2)), as a typical sigma-electron acceptor, have been studied. Electronic absorption spectra of these interactions in several organic solvents of different polarities have performed instant appearance of clear charge transfer (CT) bands. Formation constants (KCT), molar absorption coefficients (epsilonCT) and thermodynamic properties, DeltaH, DeltaS, and DeltaG, of these interactions have been determined and discussed. Electronic absorption spectra of the solutions of the synthesized pyrimidines-iodine, P-I2, CT complexes have shown the characteristic bands of the triiodide ion, I3*. UV/vis spectral tracking of these interactions have shown that by lapse of time the first formed CT complex, P-I2, is transformed to the corresponding triiodide complex, P(+)I.I3*, then, the later interacts as a new unconventional acceptor and it forms a CT complex of the form (P).(P+I.I3*). Elemental analyses of these solid complexes have indicated the stoichiometric ratio 2:2, or formally 1:1, P:I2.     

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.     

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.     

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.     

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.