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 (C60 and C70) 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 C60 and C70. Stoichiometry of both the fullerene complexes of 1 is determined to be 1:1. The magnitude of average binding constant (K) values for C70/1 and C60/1 systems is estimated to be 8705 and 3440 dm3 mol−1, respectively, which also prove that moderate value of selectivity in binding between C70 and C60 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 C60/1 and C70/1 systems in vacuo which also proves that interaction between C70 and 1 is governed by the dispersive forces associated with π–π interaction rather than electrostatic mechanism associated with charge transfer mechanism.

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► Fullerene/monoporphyrin (1) non-covalent interaction is reported in solution.
► Quenching of fluorescence intensity of 1 occurs in the presence of C60 and C70.
► Binding constant for C60/1 and C70/1 systems is enumerated.
► Life time experiment reveals static quenching phenomenon.
► MMMF calculations give strong evidence in favor of π–π interactions.