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Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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 () of all the calix[6]arenes under study have been estimated utilising CT transition energy. The experimental 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. [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: 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 CCl4 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. [Copyright &y& Elsevier]

This paper envisages the spectroscopic insights behind supramolecular interaction between xantheno-linked benzo-15-crown-5 ( 1 ) and fullerenes in solution. Estimation of binding constants ( K ) in various solvents gave rise to the highest binding affinity for C 70 complex of 1 in toluene, i.e., K = 133.000 dm 3 ⋅ mol − 1 . Studies of binding as a function of solvent ( K 1,2-dichlorobenzene < K chlorobenzene < K toluene ) correlates inversely with fullerene solubility, indicating that desolvation of fullerene is a major factor for determining the magnitude of K . DFT calculations provide convincing support in favor of high value of K for C 70 - 1 system. [ABSTRACT FROM AUTHOR]

Molecules of the coumarin family have fluorescence characteristicsthat are highly sensitive to their environment, and thus, they havebeen used as fluorescent sensors in chemical and biological systems.However, the very poor fluorescence yield of most coumarin dyes inaqueous media limits their applications. We have adopted a supramolecularstrategy to improve the fluorescence intensity of coumarin dye throughits interaction with the relatively new host cucurbit[7]uril (CB[7]).The virtually nonfluorescent coumarin 1 (Φf= 0.04)was converted into a highly fluorescent (Φf= 0.52)entity in water upon addition of the nonfluorescent host CB[7]. Variousspectroscopy techniques, namely, UV–vis absorption and steady-stateand time-resolved fluorescence spectroscopies, established the formationof a strong 1:1 dye–CB[7] inclusion complex with a high bindingconstant of (1.2 ± 0.1) × 105M–1for the dye. The stable inclusion complex of the neutral moleculewas supported by density-functional-theory- (DFT-) based quantum chemicalcalculations. Energy decomposition analysis of various interactionfactors in the host–guest complex revealed that key componentsproviding stability to the complex were electrostatic, polarization,and charge-transfer energies. These new results on the formation ofa strong inclusion complex of the versatile fluorophore coumarin 1with the nontoxic host CB[7] could lead to the design of efficientmolecular-scale biological probes, sensors, and photostable aqueousUV dye lasers. [ABSTRACT FROM AUTHOR]

Abstract: The photophysical investigation of different para-substituted tetraphenylporphyrins (TP), viz., meso-tetra(4′-hydroxyphenyl)-21H-23H-porphyrin(1),meso-tetrakis(4′-hex-5-enyloxyphenyl)-21H-23H-porphyrin(2), meso-tetrakis(4′-oct-7-enyloxyphenyl)-21H-23H-porphyrin(3) and meso-tetrakis(4′-undecyloxyphenyl)-21H-23H-porphyrin (4) revealed that except for quantum yield (φ) the para-substitution has little effect on any other photophysical properties like lifetime, excitation, emission wavelength, etc. The host–guest type interactions of these tetraarylporphyrins (TP 1–4), with [60]-fullerene (F) have been studied with 1H NMR and fluorescence spectrometric techniques in carbon tetrachloride medium. Fluorescence studies revealed that the Q band of the TPs was sufficiently quenched upon addition of F. All the fullerene/porphyrin systems were found to produce stable complexes with 1:1 stoichiometry. Binding constants (K) of all the fullerene/porphyrin complexes have been determined by fluorescence quenching method. The association constant values for 1/F have been determined from plots of the Stern–Volmer equation (103.713×104) and the Benesi–Hildebrand equation (110.440×104). It has been observed that the insertion of long chain oxo-alkenyl/alkyl group in the para position of TPs in 2, 3 and 4 diminished the K values for F by two, four and even ten times with respect to that of 1. The observed trend in variation of the binding constants was supported by a gradual variation in the shift of 1H NMR signal when measurements were carried out in CDCl3. [Copyright &y& Elsevier]

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]