Toward a Switchable Molecular Rotor. Unexpected Dynamic Behavior of Functionalized Overcrowded Alkenes

Schoevaars, Anne Marie; Kruizinga, W.; Zijlstra, R.W J; Veldman, Nora; Spek, and Anthony L.; Feringa, Ben L.

doi:10.1021/jo962210t

Cited by 106 publications

(84 citation statements)

References 29 publications

(21 reference statements)

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“…The first example ( Figure 25) is related to earlier work on coupled chiroptical switches and rotors. 55 In 33, a xylyl rotor is connected to a second generation motor. 82 The stepwise isomerization of the motor part, through the four-step 360°cycle (see Figure 21), changes the position of the propeller part with respect to the xylyl rotor, affecting its thermal rotary behavior.…”

Section: Motors On Surfaces and Molecular Transmissionmentioning

confidence: 99%

The Art of Building Small: From Molecular Switches to Molecular Motors

2007

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Molecular switches and motors are essential components of artificial molecular machines. In this perspective, we discuss progress in our design, synthesis, and functioning of photochemical and electrochemical switches and chemical and light-driven molecular motors. Special emphasis is given to the control of a range of functions and properties, including luminescence, self-assembly, motion, color, conductance, transport, and chirality. We will also discuss our efforts to control mechanical movement at the molecular level, a feature that is at the heart of molecular motors and machines. The anchoring of molecular motors on surfaces and molecular motors at work are discussed.

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Section: Motors On Surfaces and Molecular Transmissionmentioning

confidence: 99%

The Art of Building Small: From Molecular Switches to Molecular Motors

2007

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“…NaHCO 3 soln. (15 ml [20] (186 mg, 0.55 mmol) were rapidly added at r.t., and in the order mentioned. The flask was covered with Al foil, and the mixture was heated at 1008 for 3 h. After cooling to r.t., brine (10 ml) and Et 2 O (10 ml) were added under N 2 atmosphere.…”

Section: Experimental Partmentioning

confidence: 99%

“…The key step to the protected thymidine 11, bearing a C C bond in the Tx-based linkage, was a Heck reaction of the allylic alcohol 10 with 2-iodo-9H-thioxanthen-9-one (12) [19] [20]. For the analogue 13, a hydroboration ± Suzuki coupling sequence between the same starting compounds was the main step.…”

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confidence: 99%

Synthesis of Caged Nucleosides with Photoremovable Protecting Groups Linked to Intramolecular Antennae

Smirnova

Wöll

Pfleiderer

et al. 2005

Helvetica Chimica Acta

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Based on the [2-(2-nitrophenyl)propoxy]carbonyl (nppoc) group, six new photolabile protecting groups (2, 8, 9b, 16b, 25b, and 26), each covalently linked to a 9H-thioxanthen-9-one (Tx) unit functioning as an intramolecular triplet sensitizer, were synthesized. Linkers were introduced between the Me group or the aromatic ring of nppoc and the 2-position of Tx by means of classical organic synthesis combined with Pd catalyzed CÀC coupling reactions. The new photolabile protecting groups to be used in light-directed synthesis of DNA chips were attached to the 5'-O-atom of thymidine via a carbonate linkage, giving rise to the caged nucleosides 7, 11, 13, 19, 20, and 30. Introduction. ± Light-directed, massive parallel combinatorial synthesis with photoremovable protecting groups allows the fabrication of high-density DNA chips [1] [2], i.e., arrays of up to 1 million spots of different oligonucleotides on an area of ca. 1 cm 2 . Such high-density DNA chips represent highly effective diagnostic tools for a variety of genomic applications such as genotyping [3], gene-expression profiling [4], and sequencing by hybridization [5]. Several reviews on DNA chips and their application have been published [6 ± 12].The efficiency of the photolithographic technique for producing high-density DNA chips critically depends on the performance, i.e., the light sensitivity and the uniformity of the photochemical cleavage reaction of the photolabile protecting groups blocking either the terminal 5'-OH or the 3'-OH group in the growing oligonucleotides. Among the photolabile protecting groups currently in use for photolithographic DNA-chip synthesis [13], the [2-(2-nitrophenyl)propoxy]carbonyl (nppoc) group (1) developed by Pfleiderer and co-workers is a prominent example [14] [15]. It reacts in excellent yield and gives rise to a good quantum yield, the only draw-back for a higher light sensitivity being its low absorption coefficient in the near UV, where illumination is usually performed with the 366-nm Hg line. It has been shown that this problem can be overcome by triplet sensitization, e.g., with 9H-thioxanthen-9-one ( thioxanthone ), which has a high absorption coefficient at 366 nm and, on diffusional encounters, transfers its triplet energy to the photoreactive nitrobenzyl chromophore [16]. In O 2 -free solution, the rate of photodeprotection of nppoc-protected thymidine is enhanced by a factor of ca. ten, when thioxanthone is added as a sensitizer. However, since intermolecular energy transfer is rate-limited by diffusion, in the presence of O 2 , the sensitizer is mostly quenched, and the enhancement of the photoreactivity is only weak or even absent. To avoid the diffusional step in energy transfer, we synthesized new

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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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Toward a Switchable Molecular Rotor. Unexpected Dynamic Behavior of Functionalized Overcrowded Alkenes

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Cited by 106 publications

References 29 publications

The Art of Building Small: From Molecular Switches to Molecular Motors

The Art of Building Small: From Molecular Switches to Molecular Motors

Synthesis of Caged Nucleosides with Photoremovable Protecting Groups Linked to Intramolecular Antennae

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

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