Spectroscopic investigations of molecular association of cyclophanes with anthracene

Abstract

We report an improved synthesis method for the production of cyclophanes 5, 6, and 7 in higher yields of 71, 98, and 99%, respectively, compared to the previously reported 40, 30, and 70% yields, respectively. Cyclophanes C5, C6, and C7, called corrals, have different cavity sizes determined by the number of methylene spacers varying from three to five; they form inclusion complexes with neutral aromatic molecules. Therefore, we have studied their interactions with anthracene (A) using absorption, fluorescence, and Fourier transform infrared spectroscopies. The average association constants of each cyclophane with anthracene in dichloromethane were determined to be (log K) 4.24 + 0.10, 4.81 + 0.05, and 4.25 + 0.03 for the C5/A, C6/A, and C7/A systems, respectively. The binding of anthracene is favored by C6 over C5 and C7 in solution, possibly due to increased stability of the equilibrium geometry of the C6/A complex. Upon complexation low frequency spectral shifts for several transitions associated with anthracene and corral molecules were observed. The slight spectral shifts are in accord with weak intermolecular forces prevalent in the studied corral/anthracene complexes.