PHOTORESPONSIVE SUPRAMOLECULAR SYSTEMS - SYNTHESIS AND PHOTOPHYSICAL AND PHOTOCHEMICAL STUDY OF BIS-(9,10-ANTHRACENEDIYL)CORANANDS AAO(N)O(N)

Monocyclic bis-(9,10-anthracenediyl)coronands denoted AAO(n)O(n) (A = (9,10-anthracenediyl, n. indicating the number of ethyleneoxy repeatin g units between two aromatic rings) were designed as photoresponsive s ystems. Their synthesis is described; their spectroscopic properties w ere found to be in agreement with the X-ray structures. Special attent ion was devoted to AAO(5)O(5), which gives coronates with Na+ and K+. It was observed that one molecule of AAO(5)O(5), displays a positive c ooperative effect in binding two sodium cations, in contrast with prev ious reports on bicyclic coronands. Moreover, in acetonitrile, this ef fect, clear in the ground state (K-11 = 180 M(-1), K-12 240 M(-1)) was found to be stronger in the excited state (K-11 = 200 M(-1), K-12 = 5 00 M(-1)). With K+, AAO(5)O(5), generates a 1:1 complex (K approximate to 9 M(-1) in methanol). Spectroscopic properties were shown to be tr iggered by cation concentration, specifically the fluorescence emissio n which undergoes an important intensity and wavelength redistribution in favor of the excimer: the maximum wavelength is shifted from 530 n m (free Ligand) to 570 nn (sodium biscoronate), i.e., Delta nu ca. 135 0 cm(-1) and the excimer intensity is multiplied by ca. 3. The photocy clomerization (intramolecular dimerization of the anthracene nucleus) was demonstrated to be regiospecifically directed by Na+; in methanol, the free receptor exclusively generates the 9,10:1',4' photoadduct (p hi(R) approximate to 2 x 10(-4)) whereas the sodium biscoronate leads to the classical 9,10:9',10' photoadduct (phi(R) approximate to 8 x 10 (-3)). Finally, a transient kinetic analysis versus temperature allowe d the determination of the conformational mobility of the free recepto r within the nanosecond range; in the singlet excited state it is best described by the sequence M(1) --> M(2)* --> E where M* stands for t he locally excited state and E the excimer state species. At room temp erature, in methanol, excimer lifetimes were found to be as follows: f ree Ligand, 23 ns; sodium biscoronate, 165 ns; and potassium monocoron ate, 215 ns.