Synthesis of photoresponsive crown ethers having a phosphoric acid functional group as anionic cap and their selective complexing abilities toward alkali metal cations

Abstract

New photoresponsive crown ethers (3a, 3b and 3c) connected to ionizable phosphoric acid moieties by an azobenzene skeleton have been synthesized. The trans isomers are isomerized to the cis isomers by UV irradiation and the cis isomers are reversibly thermally isomerized to the trans isomers. The complexing abilities of these compounds have been estimated by measuring the cis to trans thermal isomerization rate in the presence of various alkali metals and tetramethylammonium ions and by the competitive extraction of alkali metal cations. The first-order rate constant for the thermal isomerization of cis-3a to trans-3a is remarkably suppressed in the presence of Na⁺ and the extraction ability of cis-3a for Na⁺ was greatly enhanced. In contrast, the recovery of trans-3c from cis-3c was significantly suppressed by Li⁺ and the extraction of Li⁺ by cis-3c was greatly and selectively enhanced.