title: Structural and Spectral Properties of Photochromic Diarylethenes: Size Effect of the Ethene Bridge.
abstract: The effect of the size of the ethene bridge on the structural and spectral properties of photochromic diarylethenes, which remains a poorly understood phenomenon, was studied as applied to diarylethenes containing unsymmetrical (cyclohexenone and cyclopentenone) and symmetrical (cyclohexene and cyclopentene) ethene bridges. Thiophene, oxazole, and imidazole derivatives were used as aryl moieties. An increase in the size of the ethene bridge in the cycloalkenone series was found to be accompanied by a hypsochromic shift of the absorption maximum of the photoinduced form, whereas no difference was found for cycloalkenes. A detailed analysis of the NMR spectra (including 2D experiments) revealed previously unknown effects associated with the existence of an intramolecular hydrogen bond (CH···N) between the six-membered ethene bridge and the azole substituents. The NMR experimental data obtained were confirmed by DFT quantum chemical calculations and X-ray analysis. It was found that an intramolecular hydrogen bond favors an increase of the quantum yield of the photocyclization reaction.
authors.affiliation: N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences , 47, Leninsky Prospekt, 119991 Moscow, Russian Federation.
authors.forename: Andrey G
authors.initials: AG
authors.lastname: Lvov
authors.affiliation: N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences , 47, Leninsky Prospekt, 119991 Moscow, Russian Federation.|Higher Chemical College of the Russian Academy of Sciences, D. I. Mendeleev University of Chemical Technology of Russia , 9, Miusskaya Square, 125047 Moscow, Russian Federation.
authors.forename: Alexey M
authors.initials: AM
authors.lastname: Kavun
authors.affiliation: N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences , 47, Leninsky Prospekt, 119991 Moscow, Russian Federation.
authors.forename: Vadim V
authors.initials: VV
authors.lastname: Kachala
authors.affiliation: A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences , Vavilova Street 28, Moscow, Russian Federation.
authors.forename: Yulia V
authors.initials: YV
authors.lastname: Nelyubina
authors.affiliation: Institute of Physical and Organic Chemistry, Southern Federal University , 194/2 Stachka Avenue, Rostov on Don 344090, Russian Federation.
authors.forename: Anatoly V
authors.initials: AV
authors.lastname: Metelitsa
authors.affiliation: N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences , 47, Leninsky Prospekt, 119991 Moscow, Russian Federation.
authors.forename: Valerii Z
authors.identifier: 0000-0001-9480-3565
authors.initials: VZ
authors.lastname: Shirinian