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

The new macrotricyclic ditopic bisanthracenyl receptor 1 displays mono mer and excimer type fluorescence, the latter resulting from manifold intramolecular interactions between the anthracene and amino chromopho res. 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 comple xation 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 mon omer-like emission with complete disappearance of the excimer part. Th e spectrum is then similar to that displayed by the monochromophoric r eference compound 2. The amplitude of the effect, dependent upon the c hain length n, is maximum for n = 6 and 7 and slightly decreases when n increases. The stability constants of the complexes have been determ ined by spectrophotometry. High values of the constants, ranging betwe en 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 abili ty 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+.