LINEAR MOLECULAR RECOGNITION - SPECTROSCOPIC, PHOTOPHYSICAL, AND COMPLEXATION STUDIES ON ALPHA,OMEGA-ALKANEDIYLDIAMMONIUM IONS BINDING TO A BISANTHRACENYL MACROTRICYCLIC RECEPTOR

The new macrotricyclic ditopic bisanthracenyl receptor 1 displays monomer and excimer type fluorescence, the latter resulting from manifold intramolecular interactions between the anthracene and amino chromophores. This receptor, of cylindrical shape, also presents a geometrical recognition ability toward linear dications H3N+-(CH2)n-NH3+ (S(n)2+). H-1 NMR complexation studies of 1,S(n)2+ (n = 6-10, 12) indicate the formation of mononuclear dihapto cryptates. The UV-visible absorption and fluorescence properties of 1 undergo important changes upon complexation of S(n)2+, but S-5(2+) does not significantly alter the spectra. Addition of S(n)2+ (n = 6-10, 12) produces an enhancement of the monomer-like emission with complete disappearance of the excimer part. The spectrum is then similar to that displayed by the monochromophoric reference compound 2. The amplitude of the effect, dependent upon the chain length n, is maximum for n = 6 and 7 and slightly decreases when n increases. The stability constants of the complexes have been determined by spectrophotometry. High values of the constants, ranging between 10(4) and 10(7) M-1, were obtained for the 1/1 inclusion complexes 1S(n)2+ with n = 6-10 and 12. S-5(2+) forms both 1/1 and 1/2 complexes in solution. In agreement with the other data, the complexation ability was found to be maximum for n = 6 and 7 (stability constant ca. 10(7) M-1). This behavior can be interpreted in terms of adaptability of the structurally flexible ligand toward the substrates S(n)2+.