Photophysical investigation of the supramolecular interaction between a designed bisporphyrin and N-methylfulleropyrrolidine in solution

We report the supramolecular complexation of a designed Zn 2 -bisporphyrin (1) with the fullerene derivative N-methylfulleropyrrolidine (NMFP) in toluene. UV-Vis absorption and steady-state fluorescence confirm the formation of a ground-state non-covalent complex. The job plot of a continuous variation experiment explores the formation of a 1:1 complex. Binding is evidenced from UV-Vis measurements by red-shifts of the porphyrin Soret band and appearance of isobestic points during titration. Fluorescence quenching studies reveal a moderate binding affinity, with a strength intermediate between the pristine binding of 1 with C 60 and C 70 . Time-resolved experiments indicate static quenching following the photodecay of 1 in the presence of NMFP, with an evaluated bimolecular quenching constant of 1.28×10 11 dm 3 .mol -1 .sec -1 . Density functional theoretical calculations with dispersion, namely Grimme D3, were performed in the gas phase and in a non-polar solvent model, which corroborate the spectroscopic data and highlight less optimal host-guest interactions between 1 and NMFP. The electronic structural parameters of NMFP-1 complex indicate that dispersive forces associated with π-π interaction predominate over electrostatic forces, as evidenced from the absence of charge transfer absorption band in the visible region of the electronic spectrum of NMFP-1 complex. These results provide insights into tailoring porphyrin-fullerene donor-acceptor assemblies for artificial photosynthetic and electronic applications.