Cation Enhanced trans-cis Photoisomerization in Lariat Azacrown Ethers

We describe the synthesis and effect of complexation on photochemical E (trans) to Z (cis) isomerization of lariat azacrown ethers. Lariat azacrown ethers-Ca2+ complexes are characterized by UV-Vis, 1H-NMR and fluorescence techniques. Photostationary state composition of E-Z isomers upon irradiation under direct excitation and complexation with Ca(ClO4)2, quantum yield of photoisomerization, and fluorescence properties are described. Anomalous increase in the quantum yields were observed for lariat azacrown ether-Ca2+ complexes. Fluorescence studies indicated that the highly polarized/charge transfer nature of the singlet excited state is involved in E (trans) to Z (cis) isomerization process.