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Abstract: The present paper reports the synthesis of a designed diporphyrin (1), and its supramolecular complexes with C60 and C70 in toluene medium. While UV–Vis studies reveal ground state interaction between fullerenes and 1, steady state fluorescence measurements establish quenching of fluorescence of 1 by fullerenes. Binding constants data evoke that 1 may not be employed as an efficient molecular receptor for C70 in said solvent. Time resolved emission studies establish relatively long-lived charge separated state for the C70/1 complex in non-polar solvent. Transient absorption measurements reveal that electron transfer takes place from the diporphyrin 1 to the fullerenes in solution. Cyclic voltammetric studies enable us to calculate various important physicochemical parameters like free energy of charge separation, free energy of charge recombination (ΔG CR) and free energy of radical ion-pair formation for the fullerene/1 complexes. The positive ΔG CR values for both the C60/1 and C70/1 complexes suggest that the charge-recombination process is very much susceptible in fullerene/1 complexation process and they do not correspond to the inverted region of Marcus parabola. Molecular mechanics force field calculations in vacuo establish the single projection structures of the fullerene/1 complexes and interpret the stability difference between C60- and C70 complexes of 1. 1HNMR analysis provides very good support in favor of strong binding between C70 and 1 in comparison to C60-1 system. [Copyright &y& Elsevier]

Abstract: The present paper reports the photophysical investigations on non-covalent interaction of a C60-derivative, namely, tert-butyl-(1,2-methanofullerene)-61-carboxylate (1) with H2– (H2–Pc) and Zn–phthalocyanine (Zn–Pc) in toluene medium. Well defined charge transfer (CT) absorption bands have been located in the ground state. Utilizing the CT absorption bands, various consequential physico-chemical parameters like oscillator strength, transition dipole moment, resonance energy, electronic coupling element and solvent reorganization energy, have been estimated for the complexes of 1 with phthalocyanines. The influence of 1 on the spectral characteristics of H2– and Zn–Pc are explained using a theoretical model that takes into account the interaction between electronic subsystems of 1 with the phthalocyanines (Pcs). Steady-state fluorescence experiment reveals large binding constants in the magnitude of 68,775 and 31,750dm3 mol−1, for the 1:1 complexes of 1 with H2- and Zn–Pc, respectively. Density functional theoretical calculations reveal significant redistribution of charges between 1 and Pcs. [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: 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]