Photoresponsive Crown Ethers

A photoresponsive crown ether which combines within a molecule both a crown ether and a photoisomerizable functional group changes the conformation of the crown ring in response to photoirradiation. Thus, many chemical and physical functions of the crown ether family can be controlled by on-off light switch. The syntheses and the functions (ion extraction, ion transport, etc.) of following photoresponsive crown ethers are described: azobenzene-bridged crown ethers, crown ethers containing azobenzene as a ring member, azobis(benzocrown ether)s, and anthracene-containing crown ethers. In relation to the cis-trans isomerism of azobenzene, the mechanism of thermal cis-to-trans isomerization is discussed.