Spectroscopic and theoretical insights on fullerene-octaethylporphyrin self assembled non-covalent conjugates studied in solution.

The present paper highlights the UV-Vis and fluorescence spectroscopic studies on spontaneous non-covalent interaction between a designed monoporphyrin, namely, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin (1) and fullerenes (C(60) and C(70)) in toluene medium. While UV-Vis studies reveal considerable amount of fullerene/1 interaction in ground state, steady state fluorescence study establishes remarkable quenching of fluorescence intensity of 1 in the presence of fullerenes C(60) and C(70). Stoichiometry of both the fullerene complexes of 1 is determined to be 1:1. The magnitude of average binding constant (K) values for C(70)/1 and C(60)/1 systems is estimated to be 8705 and 3440 dm(3) mol(-1), respectively, which also prove that moderate value of selectivity in binding between C(70) and C(60) complexes of 1 is resulted in our present work. The genetics of the photo-physical characteristics of fullerene/1 complexes get tremendous support from lifetime experiment, which signifies the importance of static quenching phenomenon for our presently investigated supramolecules. Life time experiment yields larger magnitude of charge separated rate constant for the fullerene/1 species in toluene. Theoretical calculations at molecular mechanics level evoke the single projection geometric structures for the C(60)/1 and C(70)/1 systems in vacuo which also proves that interaction between C(70) and 1 is governed by the dispersive forces associated with π-π interaction rather than electrostatic mechanism associated with charge transfer mechanism.