Polymer‐Bound Chiroptical Molecular Switches; Photochemical Modification of the Chirality of Thin Films

Oosterling, Michiel L.C.M.; Schoevaars, Anne Marie; Haitjema, Henk J.; Feringa, Ben L.

doi:10.1002/ijch.199600048

Cited by 22 publications

(18 citation statements)

References 37 publications

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“…However, matrix effects play a prominent role, as these strongly influence the diastereoselectivity and irradiation times required to reach the photostationary states. 14,15 This aspect will be particularly important in future applications as photoactive materials or data storage systems.…”

Section: Chiroptical Molecular Switchesmentioning

confidence: 99%

In Control of Motion: From Molecular Switches to Molecular Motors

2001

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The design of molecular systems in which controlled linear and rotary motion can be achieved under the influence of an external signal is a major endeavor toward future nanoscale machinery. In this Account we describe the development of molecular switches and the discoveries that culminated in the first light-driven molecular motor. Various chiral optical molecular switches and their use as trigger elements to control organization and functions will be discussed. The construction of the first and second generation molecular motors is presented.

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Section: Chiroptical Molecular Switchesmentioning

confidence: 99%

In Control of Motion: From Molecular Switches to Molecular Motors

2001

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“…[2,3,[6][7][8][9] BAEs have been developed as molecular switches triggered by light. [10,11] Furthermore, BAEs have been incorporated into calixarenes, [12] crown ethers, [13,14] ligands for transition-metal complexation, [15][16][17] donor-acceptor systems, [18] polymers, [19] liquid crystals, [11,20] Langmuir films, [21] and molecular rotors, [22] with the intention of adding a switchable Abstract: The nature of the thermochromic form of overcrowded bistricyclic aromatic enes (BAEs) has been controversial for a century. We report the single-crystal X-ray structure analysis of the deep-purple and yellow polymorphs of 9-(2,7-dimethyl-9H-fluoren-9-ylidene)-9H-xanthene (11), which revealed the molecules in a twisted and a folded conformation, respectively.…”

Section: Introductionmentioning

confidence: 99%

Polymorphism Versus Thermochromism: Interrelation of Color and Conformation in Overcrowded Bistricyclic Aromatic Enes

Biedermann

Stezowski

Agranat

2006

Chemistry A European J

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The nature of the thermochromic form of overcrowded bistricyclic aromatic enes (BAEs) has been controversial for a century. We report the single-crystal X-ray structure analysis of the deep-purple and yellow polymorphs of 9-(2,7-dimethyl-9H-fluoren-9-ylidene)-9H-xanthene (11), which revealed the molecules in a twisted and a folded conformation, respectively. Therefore, the deeply colored thermochromic form B of BAEs is identified as having a twisted conformation and the ambient-temperature form A as having a folded conformation. This relationship between the color and the conformation is further supported by the X-ray structures of the deep-purple crystals of the twisted 9-(9H-fluoren-9-ylidene)-9H-xanthene (10), and of the yellow crystals of the folded 9-(11H-benzo[b]fluoren-11-ylidene)-9H-xanthene (12). Based on this conclusive crystallographic evidence, eleven previously proposed rationales of thermochromism in BAEs are refuted. In the twisted structures, the tricyclic moieties are nearly planar and the central double bond is elongated to 1.40 A and twisted by 42 degrees . In the folded structures, the xanthylidene moieties are folded by 45 degrees and the fluorenylidene moieties by 18-20 degrees . Factors stabilizing the twisted and folded conformations are discussed, including twisting of formal single or double bonds, intramolecular overcrowding, and the significance of a dipolar aromatic "xanthenylium-fluorenide" push-pull structure.

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“…[3b-3f] Applications of these systems include reversible transition between nematic and cholesteric phases of liquid-crystalline material doped with optically active overcrowded alkenes, [4] as well as the photochemical modulation of chirality of thin polymer films modified with these molecules. [5] For all these applications optically active alkenes are required, which are usually obtained by preparative chiral HPLC. [6] To avoid a laborious chiral separation, a practical synthesis route towards enantiomerically pure overcrowded alkenes is a highly desired goal.…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Synthesis of Bi(thio)xanthylidene Overcrowded Alkenes

Geertsema¹,

Hoen²,

Meetsma³

et al. 2006

Eur J Org Chem

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Overcrowded alkenes are a fascinating class of inherent dissymmetric molecules that attract considerable interest for instance as chiroptical molecular switches and unidirectionally rotary motors. A practical synthesis route towards enantiomerically pure overcrowded alkenes is an important goal. We report here the development of an asymmetric synthesis of bi(thio)xanthylidenes. The upper and lower part of the desired alkenes were first coupled to a chiral template. Intramolecular coupling with partial stereocontrol, separation of diastereoisomers and subsequent removal of the templates gave stable enantiomers of bithioxanthylidene. The absolute configuration was determined by X‐ray analysis. In the case of bixanthylidene, stereocontrol during the intramolecular coupling reaction was complete, and it was found that the presence of a binaphthol bridging unit prevents the fast racemization process of the bixanthylidene, which it normally exhibited at ambient temperature. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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Polymer‐Bound Chiroptical Molecular Switches; Photochemical Modification of the Chirality of Thin Films

Abstract: Abstract. Photobistable chiral polymers were obtained by covalent attachment of inherently dissymmetric 2-hydroxy-

Cited by 22 publications

References 37 publications

In Control of Motion: From Molecular Switches to Molecular Motors

In Control of Motion: From Molecular Switches to Molecular Motors

Polymorphism Versus Thermochromism: Interrelation of Color and Conformation in Overcrowded Bistricyclic Aromatic Enes

Asymmetric Synthesis of Bi(thio)xanthylidene Overcrowded Alkenes

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