Size selective supramolecular interaction upon molecular complexation of a designed porphyrin with C60 and C70 in solution

Abstract The present work reports the case study on molecular complexation of a designed porphyrin, namely, 10,20-Bis(trans-1-amino-2-phenylethyl)-porphyrin-ZnII (1) with fullerenes C60 and C70 in toluene and 1,2-dichlorobenzene (DCB). As evidenced from both UV–vis and steady state fluorescence studies, the interaction is considered to be purely non-covalent in nature. Calculation of the binding constants value (K) of the C60 (i.e., KC60-1 = 3675 dm3·mol−1 in toluene and 4050 dm3·mol−1 in DCB) and C70 complexes of 1 (i.e., KC70-1 = 18,630 dm3·mol−1 in toluene and 20,105 dm3·mol−1 in DCB) reveal that size selective non-covalent interaction prevails in present work as selectivity of binding between C70 and C60 (KC70/KC60) is estimated to be same, i.e., KC70/KC60 ~ 5.1 measured both in toluene and DCB. Steady state fluorescence measurements elicit that the quenching of fluorescence of 1 in presence of C70 in DCB occurs via both static and dynamic quenching pathway. The values of kCSs (and φCSs) for the C60-1 and C70-1 systems are evaluated to be 8.95 × 106 s−1 (and 0.037) and 2.10 × 107 s−1 (and 0.083) in DCB, respectively, which provides very good support in favour of charge separation as well as formidable quenching in case of C70-1 system compared to C60-1 system. Explicit DFT calculations in vacuo predict the geometry on orientation of bound guest (here fullerenes) with the donor (here 1) and extend very good thermodynamic support in favour of the high value of K for the C70-1 system compared to C60-1 system with the help of theoretically calculated heat of formation (ΔHf0) value of such systems, i.e., ΔHf0 (C60-1) = −2.338 kcal·mol−1 and ΔHf0 (C70-1) = −42.802 kcal·mol−1 (side-on orientation of C70).