Study of Nonconjugated Bichromophores Linked by a Polyether Chain. I. Photochemical Synthesis of Crown‐Ethers from bis‐(9‐Anthryloxy) Polyoxaalkanes

A series of bisanthracenes (In) linked by a polyoxyethylene chain: 9‐anthryl‐O–CH2–CH2–O–CH2–(CH2–O–CH2)n–CH2–O‐9‐anthryl, where n = 1–4, was synthesized in order to investigate the bichromophoric interactions of the two aromatic rings in connection with the special properties of the chain. UV absorption spectra at room temperature in benzene and ethanol exhibit, in general, a weak hypochromicity compared with other 9–9′ bisanthracenes. Under the same experimental conditions, the fluorescence of In is twofold: (i) an emission from the locally excited state (“monomer fluorescence”) with quantum yield (ΦFM) ca. 0.10–0.17 (benzene) and 0.03–0.08 (ethanol); (ii) an excimer‐type fluorescence centered at ca. 470–515 nm, of which quantum yields (ΦFD) are in the range 0.01–0.025 (benzene) and 0.01–0.012 (ethanol). Of note is the observation of an intramolecular excimer formed from bischromophores linked by long chains (10–19 atoms). Photocyclomerization quantum yields were found to be (365 nm) 0.18–0.26 (benzene and ethanol); closure effiency is almost as high as for bisanthracenes linked by short chains. The photocyclomers, thermally unstable, are readily dissociated to In at room temperature. Several closure and reopening cycles could be observed in degassed diluted solutions. Under our conditions, addition of inorganic salts such as LiClO4 does not distinctly alter closure quantum yields of In. Rather, the complexes formed between the photocyclomers IIn (crown‐ethers) and the cations are thermally stable up to high temperatures and were not observed to revert to In either thermally or by irradiation with a low pressure mercury lamp. But the compounds In were quantitatively recovered with an excess of polar solvents which compete with the crown‐ethers to solvate the cation.