Abstract: Molecular recognition properties of three novel molecular tweezers as receptors have been investigated using diphenyl ketone and aromatic diamines. The association constants (Ka) and Gibbs free energy changes (ΔG0) have been measured by UV-visible spectroscopic titration on the complexes of these molecular tweezers with some aromatic diamines and diphenyl ketone. The results show that the supramolecular complexes formed between the tweezers and various substrates consist of 1:1 host and guest molecules. The molecular recognition ability of the receptors for diphenyl ketone and aromatic diamines is discussed in terms of size/shape-fit, complementary geometrical relationship, and the weak intermolecular forces. 1H NMR spectroscopy and computer-aided studies have been employed to elucidate the binding behavior of these molecular tweezers. Molecular modeling and 1H NMR spectroscopy studies suggest that the multiple π-π stacking and van der Waals interaction may be the main driving forces in molecular recognition. The size/shape-fit and geometyical complementary relationship between the receptor and the substrate play a pivotal role in the inclusion complextion of these guests with the molecular tweezers.

Key words: Schiff base, Molecular tweezers, Molecular recognition, UV spectral titration, ¹H NMR