Photochromic crown‐containing molecular switches of chemosensor activity

The crown‐ether functionalized 2‐( N ‐acetyl‐ N ‐arylaminomethylene)benzo[ b ]thiophene‐3(2 H )‐ones exhibit photochromic behavior involving photoinitiated Z/E ‐isomerization around the exocyclic CC bond followed by a fast thermal N → O acetyl migration and syn → anti isomerization of the resulting kinetically stable O ‐acetyl isomers. The reverse rearrangement is an acid catalyzed reaction. The addition of alkali‐earth metal ions to solutions of N ‐acyl isomers induces negligible changes in their UV/Vis spectra, which can be significantly enhanced after irradiation and conversion to the O ‐acyl isomers. The compounds obtained may be used as sensitive photodynamic chemosensors with the ‘off‐on’ mechanism for alkali‐earth ions (Ca 2+ , Ba 2+ ). Quantum‐chemical calculations using the DFT B3LYP/LanL2DZ method predict greater affinity of these sensors to Ca 2+ ions (in the gas phase) and to Ba 2+ ions (in acetonitrile). Copyright © 2007 John Wiley & Sons, Ltd.