PyC60-naphthacrown system: a new supramolecular recognition element.

Fulleropyrrolidine (PyC60) and a binaphthyl bridged crown ether macrocyclic receptor (1) undergoes spontaneous self-assembly phenomenon in solution to generate a new supramolecular recognition element having binding constant value of ∼5.83×10(4)dm(3)mol(-1). Lifetime measurement reveals a static quenching mechanism behind the deactivation of photoexcited state of 1 in presence of PyC60. The results obtained from this work would definitely reinforce bridged cyclic crown ether as one of the most suitable fragments for the molecular recognition of various macrocyclic receptor(s) in near future.

Solutions of the coupled Higgs field equations.

By an appropriate choice for the phase of the complex nucleonic field and going over to the traveling coordinate, we reduce the coupled Higgs equations to the Hamiltonian form and treat the resulting equation using the dynamical system theory. We present a phase-space analysis of its stable points. The results of our study demonstrate that the equation can support both traveling- and standing-wave solutions. The traveling-wave solution appears in the form of a soliton and resides in the midst of doubly periodic standing-wave solutions.

Influence of the energy of charge transfer on non-covalent interactions between fullerenes and a designed bisporphyrin.

The present paper reports the spectroscopic and theoretical investigations on the formation of supramolecular complexes of a designed bisporphyrin (1) with C(60) and C(70) in toluene. Absorption spectrophotometric studies establish appreciable amount of ground state electronic interaction between fullerenes and 1. The interaction is facilitated through charge transfer (CT) transition as evidenced from well defined CT absorption bands in the visible region of the electronic spectra. In our present case, the CT interaction may be claimed as one of the rare findings, especially on account of interaction between fullerenes and bisporphyrin in a non-polar solvent. Other than fullerenes C(60) and C(70), various other electron acceptors, viz., 2,3-dichloro-5,6-dicyano-p-benzoquinone, tetracyanoethylene, o-chloranil and p-chloranil form CT complexes with 1. Utilizing the CT transition energies for various electron donor-acceptor complexes of 1, vertical ionization potential (I(D)(v)) of 1 is determined to be 6.37 eV in solution. Estimation of degrees of CT, oscillator and transition dipole strengths evoke that the fullerene-1 non-covalent complexes are of neutral character in ground state. Higher magnitude of electronic coupling elements for the C(70)-1 complex compared to C(60)-1 complex indicates strong binding between C(70) and 1. Steady state fluorescence studies elicit efficient quenching of the fluorescence of 1 in presence of fullerenes. Both UV-Vis and steady state fluorescence measurements reveal large value of binding constant (K) for C(70)-1 system (∼6.94 × 10(4)dm(3)mol(-1)) than that of C(60)-1 system (K∼2.1 × 10(4)dm(3)mol(-1)). Time resolved emission studies establish charge-separated state for the fullerene-1 systems. Transient absorption measurements in the visible region establish the formation of 1(+) and fullerene(-) in toluene medium. Molecular mechanics calculations employing force field method in vacuo evoke the single projection structures of the fullerene-1 complexes and interpret the stability difference between C(60) and C(70) complexes of 1 in terms of heat of formation values of the respective complexes.

Absorption spectrophotometric, fluorescence and theoretical investigations on supramolecular interaction of a designed bisporphyrin with C60 and C70.

The present article reports the spectroscopic and theoretical investigations on supramolecular interaction between fullerenes (C(60) and C(70)) and a designed bisporphyrin, namely 1, in toluene. Job's method of continuous variation establishes 1:1 stoichiometry of the fullerene/1 complexes. Both absorption spectrophotometric and steady-state fluorescence studies reveal effective and selective interaction between fullerenes and 1 as average binding constants (K) for the C(60)/1 and C(70)/1 complexes are enumerated to be 34,700 and 359,925 dm(3) mol(-1), respectively. Large selectivity ratio in K, i.e., K(C(70))/K(C(60)), indicates that 1 acts as an effective molecular tweezers for C(70) in solution. Time-resolved fluorescence study evokes that the quenching of fluorescence of 1 by fullerenes is of static type in nature. Molecular mechanics calculations in vacuo determine the energies and single projection structures of the supramolecular systems, which provide very good support in favor of strong binding between C(70) and 1.

Photophysical insights into supramolecular interaction of a designed bisporphyrin with fullerenes C60 and C70.

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.

Spectroscopic and theoretical insights into the origin of fullerene-calix[4]pyrrole interaction.

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.