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

The present paper reports the synthesis of a designed diporphyrin (1), and its supramolecular complexes with C60 and C70 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 C70 in said solvent. Time resolved emission studies establish relatively long-lived charge separated state for the C70/1 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 (ΔGCR) and free energy of radical ion-pair formation for the fullerene/1 complexes. The positive ΔGCR values for both the C60/1 and C70/1 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 C60- and C70 complexes of 1. 1HNMR analysis provides very good support in favor of strong binding between C70 and 1 in comparison to C60-1 system.