title: The photochemistry of a bis-crown ether based on benzobis(thiazole) and its alkaline earth metal cation complexes.
abstract: Irradiation of acetonitrile solutions of the bis-crown ether E,E-2,7-bis[2-(6,7,9,10,12,13,15,16-octahydro-5,8,11,14,17-pentaoxabenzocyclopentadecen-2-yl)vinyl]-benzo[1,2-d;3,4-d']bisthiazole (hereafter, 1) gives efficient E --> Z photoisomerization (initial phi(trans --> cis) = 0.48), leading to lambda(exc)-dependent quasi-photostationary states composed primarily of E,Z and E,E isomer mixtures. Further irradiation gives [2 + 2]-cycloadducts of 1. In the presence of Ba2+ ions, essentially quantitative formation of 2:2 complexes, 1(2) x (Ba2+)2 controls the photochemical outcome. E --> Z photoisomerization of the ligand is entirely suppressed and efficient intramolecular [2 + 2]-photocycloaddition in the complexes leads to cyclobutane dimers of 1 (phiCB = 0.26). The reactivity of 1 in the presence of Mg2+ ions for which 1:2 complex formation dominates gives both cis-trans photoisomerization and enhanced photocycloaddition.
authors.affiliation: Photochemistry Center of Russian Academy of Sciences, Moscow.
authors.forename: Yu
authors.initials: Y
authors.lastname: Fedorov
authors.forename: O
authors.initials: O
authors.lastname: Fedorova
authors.forename: N
authors.initials: N
authors.lastname: Schepel
authors.forename: M
authors.initials: M
authors.lastname: Alfimov
authors.forename: A M
authors.initials: AM
authors.lastname: Turek
authors.forename: J
authors.initials: J
authors.lastname: Saltiel