title: Rotationally-hindered furyl fulgides.
abstract: Fulgides are a representative class of photochromic organic molecules which exhibit several interesting properties for diverse applications in fields such as data storage or high-resolution spectroscopy. The crystal structures of three furyl fulgides with different steric constraints were determined and for two of the compounds both the E and Z isomer structures were defined. The compounds are 3-[(E)-1,3-dimethyl-4,5,6,7-tetrahydro-2-benzofuran-4-ylidene]-4-isopropylidenetetrahydrofuran-2,5-dione, C(17)H(18)O(4), (I-E), 3-[(E)-1,3-dimethyl-5,6,7,8-tetrahydro-4H-cyclohepta[c]furan-4-ylidene]-4-isopropylidenetetrahydrofuran-2,5-dione, C(18)H(20)O(4), (II-E), and the Z isomer, (II-Z), and 3-isopropylidene-4-[(E)-1-(5-methoxy-2-methyl-1-benzofuran-3-yl)ethylidene]tetrahydrofuran-2,5-dione, C(19)H(18)O(5), (III-E), with two molecules in the asymmetric unit, and the Z isomer, (III-Z). The structures of the E and Z isomers show only little differences in the bond lengths and angles inside the hexatriene unit. Because of the strained geometry there are deviations in the torsion angles. Furthermore, small differences in the distances between the bond-forming C atoms in the electrocyclization process give no explanation for the unequal photochromic behaviour.
authors.affiliation: Organische Chemie I, Fakultät für Chemie, Universität Bielefeld, Postfach 100131, D-33501 Bielefeld, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Strübe
authors.forename: Jochen
authors.initials: J
authors.lastname: Mattay
authors.forename: Beate
authors.initials: B
authors.lastname: Neumann
authors.forename: Hans-Georg
authors.initials: HG
authors.lastname: Stammler