Spectral and theoretical studies on effective and selective non-covalent interaction between tetrahexylporphyrins and fullerenes

Abstract

The host–guest interaction of zinc(II) 5,10,15,20-tetrahexylporphyrin (Zn-THP) and its free base (H 2-THP) with fullerenes (C 60 and C 70) has been studied in toluene medium. Binding constants ( K) for H 2- and Zn-THP complexes of fullerenes were determined by UV–vis, fluorescence and NMR spectroscopic techniques. Large K values of C 70/THP complexes ( K C 70 ) were obtained in the range of 1.4–2.5 × 10 4 M −1, while those of C 60/THP complexes ( K C 60 ) were smaller (1.0–3.2 × 10 3 M −1). These results show that the K C 70 is about 10 times as large as K C 60 in both THPs ( K C 70 / K C 60 = 10). Enthalpies of formation ( Δ H f ° ) for various fullerene/THP complexes were estimated by ab initio calculations; Δ H f ° for C 60/H 2-THP, C 70/H 2-THP, C 60/Zn-THP and C 70/Zn-THP complexes are 5.82, 2.80, 2.31 and 1.54 kcal mol −1, respectively. The trends in Δ H f ° support the experimental results of selective complexation of THPs towards C 70 over C 60 and fullerenes towards Zn-THP over H 2-THP.