Complex formation between 1-chloro-4-(trifluoromethyl)benzene (guest) and 4-tert-butylcalix[4]arenes (host) distally substituted with phosphonic acid or phosphonic ester groups at the lower rim

The complexation behavior of the distally substituted phosphonic acid and phosphonic ester 4-tert-butylcalix[4]arenes (hosts) with 1-chloro-4-(trifluoromethyl)benzene (guest) was examined in chloroform. The complex stability constants (Ks) and the thermodynamic parameters of the complexation were determined by a spectrofluorometric method using Jobʹs method and vanʹt Hoff theory, respectively. A strong dependence of the host–guest interaction on the extent of distortion in the conformation of calixarene host cavity was obtained. The ‘pinched cone’ conformer of 1,3-substituted calix[4]arenes seems to form a complex with electron-deficient neutral aromatics predominantly through π–π type interaction.