Dissymmetric Molecular Tweezers in Host–Guest Complexes: Internal or External Complexation?

Abstract

The synthesis of two unprecedented series of dissymmetric molecular tweezers, with usnic acid, phenanthrene, or substituted naphthalimide arms as pincers, is described. Their association ability with the 2,4,7-trinitrofluorenone guest molecule has been quantified through NMR experiments in CD2Cl2 solution. Density Functional Theory calculations, including dispersion terms, have been carried out and rationalize both the conformational and the complexation mode behaviors of these new tweezers. With a naphthalimide and an usnic acid arms, the U-tweezer series indeed appears to behave as molecular tweezers. Conversely, in the P-tweezer series, involving a naphthalimide and a phenanthrene arm, the selected theoretical approach indicates that external complexes are more stabilized than the internal tweezed structures, corroborating experimental evidence of qualitatively different behaviors of the two series of tweezers.