Synthesis, photophysical investigations and molecular structure of the supramolecular complexes of a newly designed diporphyrin receptor with fullerenes C60 and C70 in solution

Abstract The present paper reports the synthesis of a designed diporphyrin ( 1 ), and its supramolecular complexes with C 60 and C 70 in toluene medium. While UV–Vis studies reveal ground state interaction between fullerenes and 1 , steady state fluorescence measurements establish quenching of fluorescence of 1 by fullerenes. Binding constants data evoke that 1 may not be employed as an efficient molecular receptor for C 70 in said solvent. Time resolved emission studies establish relatively long-lived charge separated state for the C 70 / 1 complex in non-polar solvent. Transient absorption measurements reveal that electron transfer takes place from the diporphyrin 1 to the fullerenes in solution. Cyclic voltammetric studies enable us to calculate various important physicochemical parameters like free energy of charge separation, free energy of charge recombination (Δ G CR ) and free energy of radical ion-pair formation for the fullerene/ 1 complexes. The positive Δ G CR values for both the C 60 / 1 and C 70 / 1 complexes suggest that the charge-recombination process is very much susceptible in fullerene/ 1 complexation process and they do not correspond to the inverted region of Marcus parabola. Molecular mechanics force field calculations in vacuo establish the single projection structures of the fullerene/ 1 complexes and interpret the stability difference between C 60 - and C 70 complexes of 1 . 1 HNMR analysis provides very good support in favor of strong binding between C 70 and 1 in comparison to C 60 - 1 system.