SYNTHESIS, X-RAY STRUCTURE, SPECTROSCOPIC AND CATION COMPLEXATION STUDIES OF MACROCYCLIC LIGANDS INCORPORATING THE 9,9'-(ETHANE-1,2-DIYL)BIS(ANTHRACENE) PHOTOACTIVE SUBUNIT

Two 9,9'-(ethane-1,2-diyl)bis(anthracene) ligands. incorporating an et hano bridge, namely the bis-anthracene coronand 1 and the bis-anthrace ne cryptand 2. respectively, have been studied in parallel to compare their binding abilities, spectroscopic and photochemical properties in the presence and absence of cations as a function of their X-ray stru cture. The ethano bridge imposes a twisted shape (torsion angles betwe en the vicinal C-H being 47 degrees for 1 and 62 degrees for 2a and 47 degrees for 2b, the two conformers of compound 2), which inhibits the cation-binding ability of 1 and attenuates that of cryptand 2 (log K- s approximate to 1.8 for Na+ or K-double dagger, approximate to 4 for Tl+ and approximate to 8 for Ag+); in CH3OH, both 1 and 2 emit essenti ally excimer-type fluorescence at lambda(max) 520-535 nm, which is red -shifted compared with that of the single crystals (approximate to 465 -480 nm) where the rotation about the CH2-CH2 bond is hindered. The pr esence of cations, which has no influence on the photocycloisomerizati on quantum yield of 1 (as expected), clearly affects that of 2. Crypta nd 2 was shown to display photochromic properties.