UV–Vis and NMR spectroscopic investigations on effective and selective non-covalent interactions between fullerenes and calix[6]arene

Abstract Ground state non-covalent interactions between a macro cyclic calixarene receptor, namely, 4-tert-butylcalix[6]arene ( 1 ), and fullerenes (C 60 and C 70 ) were studied in toluene medium by absorption spectrophotometric method. Absorption band due to the charge transfer (CT) transition have been observed in the visible region between fullerenes and 1 . Utilizing the CT absorption bands, various important physicochemical parameters like oscillator strength, resonance energy, transition dipole strength of the fullerene- 1 complexes and ionization potential of 1 is determined in present investigations. From Jobs method of continuous variation, it is observed that both C 60 and C 70 form stable 1:1 complexes with 1 . The most fascinating feature of the present study is that 1 binds selectively C 70 compared to C 60 as obtained from binding constant ( K ) data of C 60 – 1 ( K C 60 – 1 ) and C 70 – 1 ( K C 70 – 1 ) complexes, i.e., K C 60 – 1  = 32,400 dm 3 ·mol − 1 and K C 70 – 1  = 110,000 dm 3 .mol − 1 and selectivity (K C 70 – 1 /K C 60 – 1 ) = 3.4. 1 H NMR analysis provides very good support in favor of strong binding between C 70 and 1 .