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An azobenzene-bridged crown ether (2) and a polymer containing both crown ether unit and azobenzene unit (4) were synthesized. 2 bridged with trans-azobenzene (trans-2) bound an ammonium cation (5) and methyl orange salts of Li+ and Na+ preferably, whereas 2 bridged with photo-(UV) isomerized cis-azobenzene (cis-2) bound methyl orange salts of K' and Rb' preferably. The result was rationalized in terms of photoinduced expansion of the crown ether size. The binding ability of polymer 4 was also subject to photoirradiation. In particular, the crown ether units adjoining the cis-azobenzene unit lost the affinity toward Na' ion. The conformational changes of the crown ether and the polymer were conveniently monitored by following the spontaneous regeneration of trans-azobenzene in the dark. It was established on the basis of the rate measurements that (i) the conformational fluctuation of the crown ether is suppressed by K' and ammonium cations, (ii) the extension of the polymer chain in solution accompanies a large entropy increase, and (iii) AI? and AS* for the rates of regeneration of trans-azobenzene are subject to an isokinetic relationship with p = 328 K. These results indicate that photoinduced cis-trans isomerism of azobenzene, which has been found in former days, is useful as a new tool to enforce the conformational changes of crown ethers and polymers. The findings provide a possibility of controlling chemical functions of crown ethers and polymers by light. (15) Bormann, S.; Brossas, J.; Franta, E.; Gramain, P.; Kirch, M.; Lehn, J.-M. Tetrahedron 1975, 31, 2791.

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