Donor-Acceptor Complexes of (5,10,15,20-Tetra(4-methylphenyl)porphyrinato)cobalt(II) with Fullerenes C: Self-Assembly, Spectral, Electrochemical and Photophysical Properties.

The noncovalent interactions of (5,10,15,20-tetra(4-methylphenyl)porphinato)cobalt(II) (CoTTP) with C and 1-N-methyl-2-(pyridin-4-yl)-3,4-fullero[60]pyrrolidine (PyC) were studied in toluene using absorption and fluorescence titration methods. The self-assembly in the 2:1 complexes (the triads) (C)CoTTP and (PyC)CoTTP was established. The bonding constants for (C)CoTTP and (PyC)CoTTP are defined to be (3.47 ± 0.69) × 10 and (1.47 ± 0.28) × 10 M, respectively. H NMR, IR spectroscopy, thermogravimetric analysis and cyclic voltammetry data have provided very good support in favor of efficient complex formation in the ground state between fullerenes and CoTTP. PyC/C fluorescence quenching in the PyC/C-CoTTP systems was studied and the fluorescence lifetime with various CoTTP additions was determined. The singlet oxygen quantum yield was determined for PyC and the intensity decrease in the O phosphorescence for C and PyC with the CoTTP addition leading to the low efficiency of intercombination conversion for the formation of the C* triplet excited state was found. Using femtosecond transient absorption measurements in toluene, the photoinduced electron transfer from the CoTTP in the excited singlet state to fullerene moiety was established. Quantum chemical calculations were used for the determination of molecular structure, stability and the HOMO/LUMO energy levels of the triads as well as to predict the localization of frontier orbitals in the triads.