Spectroscopic and theoretical insights on determination of binding strength and molecular structure for the supramolecular complexes of a designed bisporphyrin with C60 and C70

The present article examines the binding affinity of the newly designed Zn2-bisporphyrin molecule, syn-1, towards C60 and C70 in toluene medium. The investigation is carried out by UV-vis spectrophotometric, steady state and time-resolved fluorescence spectroscopic techniques. The bisporphyrin, syn-1, serves as an effective and selective molecular tweezer for C70 as average value of binding constants (K) for the non-covalent complexes of syn-1 with C60 and C70 are estimated to be 1.65 × 104 and 1.05 × 105 dm3 · mol-1, respectively. Binding of C70 in the cleft of syn-1 is clearly demonstrated by the quantum chemical calculations at ab initio level of theory. Molecular electrostatic potential maps demonstrate significant redistribution of charges in these supramolecules. Proton NMR studies suggest that the C70 moiety remains at the shallow part of the cleft of syn-1.