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UV-Vis spectral investigations of electron donor-acceptor complexes of laser dye 2,6-Diethyl-4,4-difluoro-1,3,5,7-tetramethyl-8-(4'-hydroxyphenyl)-4-bora-3a,4a-diaza-s-indecene (1c) with chloranils and fullerenes are reported in toluene medium. Well defined charge transfer (CT) absorption bands have been located in the visible region. Oscillator strengths, transition dipole and resonance energies of the CT complexes have been estimated. Vertical ionization potential of 1c has been determined utilizing Mulliken's equation. A possible mechanism for the interaction between electronic subsystems of chloranils, [60]- and [70]fullerenes with three different BODIPY dyes (1a, 1b and 1c shown in Fig. 1) have been discussed in comparing the parameters like degree of charge transfer and binding constant in nonpolar toluene. Comparison of 1c complexes is done with DFT/B3LYP/6-31G optimized gas phase geometries., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The present paper reports non-covalent interaction between fullerenes (C(60) and C(70)) and a designed bisporphyrin (1) in p-xylene in absence and presence of silver nanoparticles (AgNp) having diameter ∼5-15 nm. Both UV-vis and fluorescence experiments reveal reduction in the average binding constant (K(av)) value for C(60)-1 (K(C60-)(1)=27,980 dm(3)mol(-1)) and C(70)-1 systems (K(C70-)(1)=115,020 dm(3)mol(-1)) in presence of AgNp, i.e., K(C60-)(1)(-AgNp)=22,465 dm(3)mol(-1) and K(C70-)(1)(-AgNp)=30,830 dm(3)mol(-1). Dynamic light scattering experiment gives clear indication regarding formation of larger aggregates as a result of electrostatic attraction between porphyrin-based supramolecule and AgNp in solution. Scanning electron microscope measurement reveals formation of molecular cluster comprising C(70)-1-AgNp composite., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The present paper reports the spectroscopic investigations on non-covalent interaction of fullerenes C(60) and C(70) with a designed trihomocalix[6]arene (2) in toluene. UV-vis studies reveal appreciable ground state interaction between fullerenes and 2. Jobs method of continuous variation establishes 1:1 stoichiometry for fullerene-2 complexes. Binding constant (K) data reveals that 2 binds C(70) more strongly compared to C(60), i.e. K(C60-2)-47,540 dm(3)mol(-1) and K(C70-2)-86,360 dm(3)mol(-1). Proton NMR studies provide very good support in favor of strong binding between C(70) and 2. Estimation of solvent reorganization energy (R(S)) evokes that C(70)-2 complex is stabilized more compared to C(60)-2 complex as R(S(C60-2))- -1.162 eV and R(S(C70-2))- -1.244eV. Semiempirical calculations at third parametric level of theory in vacuo evoke the single projection structures of the fullerene-2 complexes and interpret the stability difference between C(60) and C(70) complexes of 2 in terms of enthalpies of formation values., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The present article reports for the first time on supramolecular interaction between fullerenes (C60 and C70) and a designed monoporphyrin in solution, e.g., 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine (1), in absence and presence of silver nanoparticles (AgNp) having varying diameter of range between 3 and 7 nm. Ground state electronic interaction between fullerenes and 1 has been evidenced from the observation of decrease in the intensity of the Soret absorption band of 1 after complexation with C60 and C70 in toluene. However, in presence of AgNp, extent of decrease in the intensity of Soret absorption band of 1 has been reduced following its complexation with fullerenes. Steady state fluorescence measurements establish quenching of fluorescence of 1 by fullerenes and the most interesting aspect of the present work is that quenching efficiencies of C60 and C70 are found to be less in presence of AgNp. Steady state fluorescence measurement reveals reduction in the binding constant (K) value for both C60-1 (KC60-1=2355 dm3 mol(-1) and C70-1 complex (KC70-1=11,980 dm3 mol(-1)) in presence of AgNp (KC60-1=340 and KC70-1=7380 dm3 mol(-1)). The new physical insight of the present studies is that 1 acts as excellent discriminator molecule for C70 in presence of AgNp as selectivity in binding is estimated to be ∼21.7 in presence of AgNp compared to the situation when fullerene-1 mixture does not contain any AgNp (i.e., selectivity in binding=∼5.0) in solution. Time-resolved fluorescence studies establish the role of static quenching mechanism behind fluorescence decay of 1 by fullerenes in absence and presence of AgNp. Magnitude of rate constant for charge separation and quantum yield of charge separation indicates that C70-1 complex exhibits highest value of such parameters in absence of AgNp compared to the situation when AgNp particles are present in the composite mixture of C70 and 1. Dynamic light scattering (DLS) measurement reveals while particle size of AgNp is estimated to be ∼4.8-5.0 nm in presence of 1, the size of the AgNp particles in 1 become larger in presence of C60 (∼13.0 nm) and C70 (∼37.0 nm) solution in toluene. Conductance measurement establishes that AgNp particles reduce the generation of electrical conductivity value for both C60-1 and C70-1 systems in toluene with respect to time; the rate of decrease of electrical conductivity become much slower in presence of C70-1 complex. Scanning electron microscopic experiment provides excellent support for DLS measurements regarding increase in the size of the nanoparticles in presence of C60 and C70. Transmission electron microscope clearly demonstrates that the electrostatic attraction between porphyrin-based supramolecules and silver nanoparticles is very much responsible behind the formation of larger aggregates. Semiempirical PM3 calculations in vacuo establish the single projection structures for the fullerene-1 complexes and well interpret the stability difference between C60- and C70-complexes of 1 in terms of heat of formation values of the respective complexes., (Copyright © 2011 Elsevier B.V. All rights reserved.)

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)., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The present paper reports, for the first time, supramolecular interaction of meso-octamethyl calix[4]pyrrole (1) with fullerenes C(60) and C(70) in solutions having varying polarity (e.g., toluene, 1,2-dichlorobenzene and benzonitrile and chloroform). The interaction is facilitated through charge transfer (CT) transition as evidenced from well-defined CT absorption bands in the visible region of absorption spectroscopy. Utilizing the CT transition energy for the complexes of 1 with various electron acceptors, we have determined the ionization potential of 1. Estimation of degrees of CT, oscillator, and transition dipole strengths suggest that the complexes are almost of neutral character in ground state. Higher magnitude of electronic coupling element value for the C(70)-1 complex compared to C(60)-1 indicates strong binding between C(70) and 1. Binding constants (K) of the fullerene-1 complexes have been determined from UV-vis investigations, which indicate high selectivity of 1 toward C(70). Extraordinary large K value of the C(70)-1 complex in chloroform medium (K approximately 1.43 x 10(6) dm(3) x mol(-1)) establishes that a polar environment facilitates such interaction. Both proton NMR and liquid IR studies provide very good support in favor of strong binding between C(70) and 1. (13)C NMR study proves that C(70) binds 1 with its equatorial belt, which substantiates the role of pi-pi interaction behind such strong interaction (i.e., high K value). Semiempirical theoretical calculations at the third parametric level (PM3) explore the stability difference between C(60)- and C(70)-1 complexes. PM3 calculations also reveal that approach of C(70) toward 1 is directed in side-on manner rather than in a conventional end-on alignment.

The host-guest interactions of various tetraarylporphyrins (TP), viz., 5,10,15,20-tetraphenyl-21H,23H-porphyrin (1), 5,10,15,20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (2) and 5,10,15,20-tetrakis(dodecyloxyphenyl)-21H,23H-porphyrin (3) with C60 and C70 have been studied by 1H NMR, UV-vis and fluorescence spectroscopic techniques in toluene medium. All the fullerene/porphyrin complexes are found to be stable with 1:1 stoichiometry. Binding constants (K) of all the fullerene/porphyrin complexes have been determined by fluorescence quenching experiment. The trend in K values revealed that the presence of long chain n-alkyl group in tetraarylporphyrin effectively and remarkably increases the selectivity ratio of C70 over C60. Theoretical calculations have extended a good support in interpreting the stability difference between various fullerene/TP complexes.

To improve the selectivity ratio of C70 over C60, a new designer molecule, viz., 3-fluoromesotetraphenylporphyrin (1) has been reported in the present investigations. Fluorescence studies reveal that the Q-absorption band of 1 gets sufficient quenching effect upon addition of both C60 and C70. Binding constants (K) of the C60/1 and C70/1 complexes are estimated to be 580 and 10,800 dm3 mol(-1), respectively. Thus, K(C70)/K(C60) is approximately 19 which is very large and even comparable with other macrocyclic host molecules like calix[5]arene, azacalix[m]arene[n]pyridine, cyclotriveratrylenophane and calixarene bisporphyrin. 1H NMR chemical shift measurements show that the -NH- proton of 1 suffers more shifts in presence of C70 compared to C60. This finding also offers a good support in favor of high K value for C70/1 complex as well as large selectivity ratio of C70 over C60.

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.

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.

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.

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.

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.

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.

[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.

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., (Copyright 2003 Elsevier B.V.)

[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.

Abstract: The present article reports for the first time on supramolecular interaction between fullerenes (C60 and C70) and a designed monoporphyrin in solution, e.g., 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine (1), in absence and presence of silver nanoparticles (AgNp) having varying diameter of range between 3 and 7nm. Ground state electronic interaction between fullerenes and 1 has been evidenced from the observation of decrease in the intensity of the Soret absorption band of 1 after complexation with C60 and C70 in toluene. However, in presence of AgNp, extent of decrease in the intensity of Soret absorption band of 1 has been reduced following its complexation with fullerenes. Steady state fluorescence measurements establish quenching of fluorescence of 1 by fullerenes and the most interesting aspect of the present work is that quenching efficiencies of C60 and C70 are found to be less in presence of AgNp. Steady state fluorescence measurement reveals reduction in the binding constant (K) value for both C60–1 () and C70–1 complex () in presence of AgNp (). The new physical insight of the present studies is that 1 acts as excellent discriminator molecule for C70 in presence of AgNp as selectivity in binding is estimated to be ∼21.7 in presence of AgNp compared to the situation when fullerene–1 mixture does not contain any AgNp (i.e., selectivity in binding=∼5.0) in solution. Time-resolved fluorescence studies establish the role of static quenching mechanism behind fluorescence decay of 1 by fullerenes in absence and presence of AgNp. Magnitude of rate constant for charge separation and quantum yield of charge separation indicates that C70–1 complex exhibits highest value of such parameters in absence of AgNp compared to the situation when AgNp particles are present in the composite mixture of C70 and 1. Dynamic light scattering (DLS) measurement reveals while particle size of AgNp is estimated to be ∼4.8–5.0nm in presence of 1, the size of the AgNp particles in 1 become larger in presence of C60 (∼13.0nm) and C70 (∼37.0nm) solution in toluene. Conductance measurement establishes that AgNp particles reduce the generation of electrical conductivity value for both C60–1 and C70–1 systems in toluene with respect to time; the rate of decrease of electrical conductivity become much slower in presence of C70–1 complex. Scanning electron microscopic experiment provides excellent support for DLS measurements regarding increase in the size of the nanoparticles in presence of C60 and C70. Transmission electron microscope clearly demonstrates that the electrostatic attraction between porphyrin-based supramolecules and silver nanoparticles is very much responsible behind the formation of larger aggregates. Semiempirical PM3 calculations in vacuo establish the single projection structures for the fullerene–1 complexes and well interpret the stability difference between C60- and C70-complexes of 1 in terms of heat of formation values of the respective complexes. [Copyright &y& Elsevier]

The present paper reports the results of a photophysical investigation of a designed monoporphyrin ( 1) and its supramolecular complexes with C, C and derivatized fullerenes, namely tert-butyl-(1,2-methanofullerene)-61-carboxylate ( 2) and [6,6]-phenyl C 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 C/ 1, C/ 1, 2/ 1 and 3/ 1 complexes are estimated to be 300, 20770, 1150 and 13170 dm⋅mol, 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. [ABSTRACT FROM AUTHOR]

The present article reports the host-guest complexation of a calix[4]arene derivative, namely 4- iso-propyl-calix[4]arene ( 1), with fullerenes (both C and C) in toluene and benzonitrile solutions. It is observed that the charge-transfer (CT) absorption bands are located in the ground state for the C and C complexes of 1. By utilizing the CT absorption bands, various important physicochemical parameters like the oscillator strength, resonance energy, transition dipole moment, electronic coupling element and solvent reorganization energies have been estimated for the C- 1 and C- 1 complexes. The CT transition energy is very helpful for determining the vertical ionization potential of 1 in solution. Jobs method of continuous variation was used to establish 1:1 stoichiometry for the fullerene complexes of 1. The most fascinating feature of the present study is that 1 binds C preferentially compared to C as obtained from binding constant ( K) data. The effect of solvent on the complexation of fullerenes (C and C) with 1 is clearly observed from the trend in the K values: in toluene [InlineEquation not available: see fulltext.] and [InlineEquation not available: see fulltext.] whereas in benzonitrile, [InlineEquation not available: see fulltext.] and [InlineEquation not available: see fulltext.]. Molecular mechanics force field (MMMF) calculations reveal fascinating features regarding the binding pattern of fullerenes towards 1 in vacuo in terms of enthalpy of formation. MMMF calculations establish that during C- 1 complexation, C is directed in an end-on manner rather than the traditional side-on pattern. [ABSTRACT FROM AUTHOR]

Ground state non-covalent interactions between a newly designed macrocyclic 1,3,5-trihomo calix[6]arene receptor, designated as 1, and the C and C fullerenes have been studied in toluene solutions. It was observed that the absorbances of both C and C solutions increased upon the addition of increasing concentrations of compound 1. Job's method of continuous variation established 1:1 stoichiometry for these fullerene- 1 complexes. The binding constant ( K) data reveal that compound 1 binds to C more strongly compared to C, i.e., $K_{C60\mbox{-}\boldsymbol{1}} = 230~\mathrm{dm}^{3}{\cdot}\mathrm{mol}^{-1}$ and $K_{C70\mbox{-}\boldsymbol{1}}= 517~\mathrm{dm}^{3}{\cdot}\mathrm{mol}^{-1}$. Proton NMR analysis provides very good support for strong binding between C and 1. Estimations of the solvent reorganization energy ( R) suggest that the C- 1 complex is stabilized more than the corresponding C- 1 complex, with $R_{S(C60\mbox{-}\boldsymbol{1})} = -1.970~\mathrm{eV}$ and $R_{S(C70\mbox{-}\boldsymbol{1})}= -2.300~\mathrm{eV}$. Molecular mechanics force field method calculations established that the binding pattern of C towards 1 occurs in the side-on rather than end-on orientation, and that the C- 1 complex gains 5.23 kJ⋅mol of extra stabilization energy with this side-on geometrical arrangement. [ABSTRACT FROM AUTHOR]

Abstract: Emission spectroscopic studies were performed to follow the intermolecular complexation of [60]- and [70]-fullerene as well as of o- and p-chloranils with meso-tetra-2-chlorophenylporphyrin (clTP) in non-interacting toluene medium. This has revealed different quenching mechanisms to be operational for these two groups of compounds. The ground state association constants of the intermolecular complexes were determined on the basis of the Stern–Volmer (SV) equation of fluorescence quenching. Theoretical justification for complex formation in terms of charge distribution, HOMO–LUMO interactions were provided in terms of DFT and ab initio Hartree–Fock calculations. [Copyright &y& Elsevier]

Abstract: Solution state electronic (UV–Vis) and fluorescence spectra of the electron donor–acceptor complexes of 5,10,15,20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (TP) with [60]- and [70]fullerenes have been investigated in chloroform medium. Lifetimes of 0.5 ns and 0.85 ns are found for [60]fullerene/TP and [70]fullerene/TP complexes, respectively. The donor–acceptor electronic coupling (V) for the above two complexes have been estimated by two independent methods resulting in a relatively large value of ≈2−4×103 cm−1, i.e., between 5000 and 2500 nm, which is resulted due to the close proximity of the porphyrin and fullerenes molecules. Electronic coupling element determined by absorption spectrophotometric method corroborates fairly well with those obtained from emission measurements. [70]fullerene/TP complex is shown to exhibit higher value of electronic transition moment. [Copyright &y& Elsevier]

Abstract: To improve the understanding of solution properties of [70]fullerene in aromatic solvents, binary systems of [70] fullerene with a series of anisole, viz., anisole, m-bromoanisole and p-bromoanisole have been studied in CCl4 medium by NMR spectroscopy. The complexes of [70]fullerene with the anisoles are shown to exhibit 1:1 ([70]fullerene:anisole) stoichiometry. Formation constants (K) of the above molecular complexes are determined using NMR spectroscopic technique. The K values of [70]fullerene/anisole, [70]fullerene/m-bromoanisole and [70]fullerene/p-bromoanisole give a good correlation of linear free energy relationship (L.P. Hammett, Chem. Rev. 53 (1953) 191). [Copyright &y& Elsevier]

To improve the understanding of the formation of electron donor–acceptor complexes of [60]- and [70]fullerenes, EDA interaction of [60]- and [70]fullerenes and some other electron acceptors with benzoyl acetone were studied in CHCl3 medium using absorption spectrophotometry. An absorption band due to charge transfer (CT) transition is observed in the visible region. The vertical ionization potential of the benzoyl acetone was determined from the CT transition energy. Oscillator and transition dipole strengths have also been calculated. Trends in the formation constant for the complexes [60]- and [70]fullerenes with benzoyl acetone were discussed in terms of enthalpies and entropies of formation. [Copyright &y& Elsevier]

Abstract: The ground and excited states interaction of 4,4-difluoro-1,3,5,7-tetramethyl-2,6-diethyl-8-phenyl-4-bora-3a,4a-diaza-s-indacene (2), the meso-phenyl congener of the well-known boradipyrromethene (bodipy) dye PM567 (1) with C60 and C70 (F) was investigated in non-polar (toluene) and polar coordinating (benzonitrile) solvents. This dye 2 can efficiently recognize C70 in both the solvent media. It is the first report of wavelength ratiometric sensing of fullerenes (F) in both the ground and excited state. The dye (2) showed higher binding selectivity with C70 over C60 in both benzonitrile and toluene having selectivity ratio C70/C60~100 and ~6 respectively. Interestingly, the binding preference of the dye 2 with C70/C60 was opposite to that observed with the dye 1 (possessing a meso-methyl group), revealing that the selectivity can be tuned by subtle changes in the bodipy structure. The results were rationalized by 1H NMR and DFT based calculation of the HOMO–LUMO interactions of the adduct. [Copyright &y& Elsevier]

Abstract: The present article reports the spectroscopic investigations on non-covalent interaction of fullerenes C60 and C70 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 C60 compared to C70 as obtained from binding constant (K) data of C60-1 (K C60-1 ) and C70-1 (K C70-1 ) complexes which are enumerated to be 265,000dm3 mol−1 and 63,430dm3 mol−1, respectively, and selectivity in binding (K C60-1 /KC70-1 ) 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 C60-1 and C70-1 complexes are estimated to be 80,760 and 68,780dm3 mol−1, respectively, with selectivity in binding (KC60-1 /KC70-1 ) ∼1.18. 1H NMR analysis provides very good support in favor of strong binding between C60 and 1. The high value of K value for C60-1 complex indicates that 1 forms an inclusion complex with C60. [Copyright &y& Elsevier]

Abstract: Ground state interactions between a macrocyclic calixarene receptor, namely, 4-tert-butyl calix[5]arene (1) with fullerenes C60 and C70, were studied by absorption spectrophotometric method in toluene medium. Well defined charge transfer (CT) absorption bands were located for the complexes of C60 and C70 with 1. Utilizing the CT absorption bands, various important physico-chemical parameters like oscillator strength, resonance energy and electronic coupling elements were determined for fullerene-1 complexes. It was observed that 1 binds preferentially C70 compared to C60 as obtained from binding constant (K) data, i.e., =23600dm3 mol−1 and =94460 dm3 mol−1. Proton NMR investigations also provided a very good support in favor of strong complexation between C70 and 1. PM3 calculations established that binding pattern of C70 towards 1 was end-on rather than side-on as C70/1 complex gained 2.43kJmol−1 of extra stabilization energy in case of its end-on orientation rather than traditional side-on approach. [Copyright &y& Elsevier]

Abstract: A detailed UV–Vis spectrometric and thermodynamic studies were done to look insight into the nature of molecular interactions of the electron donor–acceptor complexes of C60 and C70 with 5,10,15,20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (1) in chloroform and toluene. Charge transfer (CT) absorption bands were located in the visible region and vertical ionization potential of 1 was determined utilizing CT transition energy. Low values of oscillator and transition dipole strengths suggested that the complexes were almost of neutral character in ground states. The high binding constant value for the C70–1 complex indicated high selectivity of 1 molecule towards C70. Experimental as well as theoretically determined of enthalpies of formation value substantiated the trend in K values for fullerene–1 complexes. [Copyright &y& Elsevier]

Abstract: The present investigations report the UV–vis absorption studies on electron donor–acceptor (EDA) complexes of 5,10,15,20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (TP) with C60, C70 and some other electron acceptors in chloroform medium. Charge transfer (CT) absorption bands of the above mentioned complexes have been located in the visible region and vertical ionization potential of TP has been determined from the trend in CT transition energy. CT is very weak in these complexes as revealed from very low value of oscillator and transition dipole strengths. All the complexes are found to stable with 1:1 stoichiometry. Binding constants (K) for the fullerene complexes of TP are determined at four different temperatures from which enthalpies and entropies of binding of the processes have been estimated. The high K value for the C70/TP complex as well as C70/C60 selectivity ratio at room temperature supports the understanding of EDA complex binding between fullerenes and porphyrin. Ab initio theoretical investigations provide a rational support in favor of strong complexation between C70 and TP. [Copyright &y& Elsevier]

Abstract: A detailed UV–Vis spectrophotometric, thermodynamic and NMR studies have been carried out to look insight into the nature of molecular interactions of the electron donor–acceptor complexes of [60]fullerene with three different polycyclic aromatic hydrocarbon (PAH) molecules in CCl4 medium. 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 vertical ionization potentials of the donors studied. The influences of the PAH on the absorption spectrum of [60]fullerene are studied. The experimental results have been explained using a theoretical model that takes into account the interaction between electronic subsystems of PAH with [60]fullerene. Formation constants (K) of the [60]fullerene/PAH complexes are determined spectrophotometrically (utilizing Benesi–Hildebrand equation) at four different temperatures and by 1H NMR spectroscopic technique. Trend in the formation constant values for the [60]fullerene/PAH complexes are discussed in terms of enthalpies and entropies of formation. Free energies of formation values for the [60]fullerene/PAH systems as well as ab initio calculation suggest that nature of substitution and steric effect in the PAH systems play vital role in formation of EDA complexes with [60]fullerene. [Copyright &y& Elsevier]