Abstract
The metal cation (Ba++) binding ability of a family of designed nonconjugated bichromophoric [bis(para-phenylene)- or bis(para-diphenylene)]polyoxamacrocyclic coronands has been studied in acetonitrile in the ground state and in the singlet excited state. The association constants (K) at ambient temperature have been determined from UV absorption and fluorescence data, by use of the LETAGROP-SPEFO programme. The ground state complexes exhibit 1:1 or 1:1 and 2:1 (cation/ligand) stoichiometries and a large variety of association constants, as well as diverse cooperative effects. Remarkably, TTO5O5 {1,4,7,10,13,21,24,27,30,33-decaoxa[13.15]-(1,4)benzenophane} shows a strong binding ability (log β = 10.3) with a positive cooperativity. The apparent association constants measured from stationary fluorescence data were found to be lower in some cases than those observed in the ground state; these results strongly suggest that a transitory photodecomplexation between the metal cation and the phenolic oxygen atoms occurs in the S1 state. An X-ray structure analysis was performed on the barium complex of a related podand and the Ba++ coordination number was found to be 10.
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