Synthesis and photophysical properties of fluorescent anthracenophanes incorporating two polyoxadioxoalkane chains
Abstract
Anthracene macrolides In(n= 1–4) display dual fluorescence (‘monomer’/excimer) sensitive to the number of links of the chain n and temperature. The excimer fluorescence quantum yield is particularly high (0.24–0.39 in toluene) in comparison with those of related anthracenophanes or bichromophores. A thermodynamic study of the fluorescence emission has enabled us to evaluate the activation energy of excimer formation (25.1–27.2 kJ mol–1 for n= 1, 3, 4, and 15.0 kJ mol–1 for n= 2), its enthalpy of stabilization (–14.2 to –21.7 kJ mol–1), and the repulsive potential in the ground state between two anthracenes after radiative deactivation of the intramolecular excited complex (38.5–53.1 kJ mol–1). These values are discussed as a function of n and compared with literature data.
The spectroscopic properties of In were found to be weakly cation dependent except for I4 and Sr2+ or Ba2+ where moderate effects were detected in UV absorption or fluorescence emission spectra. The failure to encapsulate the alkali and alkaline-earth cations is ascribable to the rigidity of the system which presumably hinders the formation of a stable co-ordinating sphere around the cation.
The fluorescence emission of the single crystals is described and correlated with the molecular packing mode. The excimer-type emitting crystals (n= 2 and 4) contain pairs or stacks of aromatic rings whereas ‘monomer’-type emitting crystals do not show any important overlap between anthracenes.