Conformational Study of 2,2‘-Homosubstituted 1,1‘-Binaphthyls by Means of UV and CD Spectroscopy

Bari, Lorenzo Di; Pescitelli, Gennaro; Salvadori, Piero

doi:10.1021/ja990326b

Cited by 238 publications

(194 citation statements)

References 70 publications

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“…That alterations in this dihedral angle can impact the CD and optical rotation behaviors of smaller chiral binaphthylene derivatives has been widely demonstrated in a number of earlier reports. [23][24][25] An inspection of the twin plots shown in Figure 3 clearly reveals that the measured rotation magnitudes for polymers 1(R) through 6 dissolved in DMAC are linearly related to the loading of the (R)-binaphthylene groups positioned along the polymer backbone. This trend in the chiroptical data holds both before and after near-UV light exposure.…”

Section: Stimuli-responsive Chiroptical Behaviormentioning

confidence: 96%

Stimuli-Responsive Polymers VI. Azobenzene Modified Copolyaramides with Chiral Helical Geometries: Influence of Rigid, Helix-Disrupting Segments on Physiochemical and Chiroptical Behavior

Jaycox

2002

Polym J

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ABSTRACT:Polymers comprised of alternating trans-4,4 -azobenzene and helix directing (R)-2,2 -binaphthylene backbone linkages adopt single handed helical conformations in solution that are reversibly distorted by light and heat regulated trans ↔ cis isomerization processes. The replacement of (R)-binaphthylene backbone groups with helixdisrupting 4,4 -diphenylfluorene segments affords permanent changes in some of the properties exhibited by this family of optically active materials. Polymer solubilities in organic solvents like THF and acetone are significantly diminished while thermal stabilities and photophysical behavior remain largely unchanged. Optical rotation magnitudes measured at the sodium D-line drop in a linear manner with the loss of the atropisomeric binaphthylene linkages. However, all of the polymer variants exhibit stimuli-responsive chiroptical behavior when evaluated in DMAC or THF solution environments. Specific rotation magnitudes are reversibly diminished by the near-UV light induced trans → cis isomerization reaction. Optical rotatory power is restored by reverse cis → trans isomerization processes triggered by heat or by visible light illumination. That stimuli-responsive chiroptical properties are exhibited by all polymer variants regardless of their monomer compositions indicates that global helical order along the polymer backbone is not necessarily required for this effect. Rather, isomerization induced perturbations to the local dihedral angles residing in the atropisomeric binaphthylene main chain segments likely serve as the genesis for photo-and thermo-regulated behavior in these materials.KEY WORDS Stimuli-Responsive Chiroptical Behavior / trans-cis Azobenzene Isomerization / Helical Polymers / Circular Dichroism / Optical Rotation / Exciton Coupling / Cardo Polymers / Macromolecules endowed with single-handed helical geometries can be prepared by a variety of synthetic methods. Monomers based on chiral 1,1 -binaphthylenes, 1,1 -biphenylenes and other axially dissymmetric ring systems provide convenient access to condensation polymers with chiral helical motifs. The polycondensation of (R)-(+)-1,1 -binaphthyl-2,2 -diamine with terephthaloyl chloride was first reported by Schulz and Jung over thirty years ago. 1 The resulting polyaramide exhibited significant optical rotatory power that was attributed to the presence of a single helical screw sense along the polymer's conformationally restricted backbone. In the decades that have followed, a variety of other optically active macromolecules have been assembled from atropisomeric, helix-directing monomers using this same generalized approach. 2 Earlier, this laboratory reported the preparation of a number of helical trans-azobenzene modified polyaramides from both (R)-and (S )-1,1 -binaphthyl-2,2 -diamine. 3, 4 Some of these materials were specifically designed to undergo reversible helix order ↔ disorder transitions in response to multiple trans ↔ cis azobenzene isomerization reactions triggered within the polymer's main chain. [5]...

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Section: Stimuli-responsive Chiroptical Behaviormentioning

confidence: 96%

Stimuli-Responsive Polymers VI. Azobenzene Modified Copolyaramides with Chiral Helical Geometries: Influence of Rigid, Helix-Disrupting Segments on Physiochemical and Chiroptical Behavior

Jaycox

2002

Polym J

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“…[20] Furthermore, comprehensive analysis of their exciton circular dichroism (CD) spectra has been reported in the literature; [21,22] both b and CD are deeply influenced by the dihedral angle between the naphthalene chromophores. [21][22][23] We have also studied m-bis(azo)benzene derivatives 5 and 6 with chiral pendant groups in the hope of obtaining induction of an helical structure of the foldamer type [24] and hence, possibly, high helical twisting powers.…”

Section: Introductionmentioning

confidence: 99%

“…[21][22][23] We have also studied m-bis(azo)benzene derivatives 5 and 6 with chiral pendant groups in the hope of obtaining induction of an helical structure of the foldamer type [24] and hence, possibly, high helical twisting powers. Compound 7 was synthesised to observe better effects due to the restricted mobility of the system.…”

Section: Introductionmentioning

confidence: 99%

The Control of the Cholesteric Pitch by Some Azo Photochemical Chiral Switches

Pieraccini

Gottarelli

Labruto

et al. 2004

Chemistry A European J

115

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A few chiral azo compounds, which undergo reversible photochemical switching, are presented. Of these, the most interesting contain the binaphthyl moiety and belong to the C2 (derivatives 1 and 2) or C1 symmetry group (derivatives 3 and 4). These binaphthyl compounds display intense CD and high beta values. Photochemical switching has profound effects on both the CD and beta values of these compounds; in the case of compound 3, the sign of beta changes upon isomerisation. Compound 2 has, to our knowledge, the highest beta of the switches reported in the literature and also seems the most interesting owing to its fast response to photochemical stimuli. Nematic phases can be transformed into cholesteric phases with reflection bands in the visible region by doping with reasonable amounts of 1 and 2. The reflection colours can be changed reversibly by photoisomerisation of the switches. Thermal reversion of the colourless UV photostationary state to the green isomeric EE state or to intermediate coloured states is temperature dependent. This can allow the thermal history of a sample to be traced.

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“…As a consequence, the observed spectrum about 220 nm is reinforced rather than canceled because it is due to the envelope of the whole conformational distribution of q. [29] The situation is dramatically different when the ligand is engaged in the complex, because it must assume a well-defined conformation and no conformational decoupling between neighboring chromophores can be envisaged. Not surprisingly, the UV-ECD spectrum of M40 undergoes profound changes on adding Yb (TfO) 3 , as shown in Figure 5.…”

Section: Wwwchemeurjorgmentioning

confidence: 99%

Reversible Mutarotation in a Macrocyclic Ytterbium Complex

Ballistreri

Gentile

Pappalardo

et al. 2010

Chemistry A European J

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M40 is a four-fold symmetry macrocyclic ligand endowed with axial and central chiral elements, all of R configuration. It promptly binds late lanthanides (Yb(III) and Lu(III) ) yielding a negative helicity, as witnessed by NIR-electronic circular dichroism. In the course of a few hours, a new conformation of the complex takes over, which has opposite helicity and allows for a dynamic free-bound equilibrium. Upon slow solvent evaporation, the original conformation is retrieved and the whole dynamic process can be started again, as in a sandclock, allowing one to envisage applications as a time-marker chiral switch.

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Conformational Study of 2,2‘-Homosubstituted 1,1‘-Binaphthyls by Means of UV and CD Spectroscopy

Cited by 238 publications

References 70 publications

Stimuli-Responsive Polymers VI. Azobenzene Modified Copolyaramides with Chiral Helical Geometries: Influence of Rigid, Helix-Disrupting Segments on Physiochemical and Chiroptical Behavior

Stimuli-Responsive Polymers VI. Azobenzene Modified Copolyaramides with Chiral Helical Geometries: Influence of Rigid, Helix-Disrupting Segments on Physiochemical and Chiroptical Behavior

The Control of the Cholesteric Pitch by Some Azo Photochemical Chiral Switches

Reversible Mutarotation in a Macrocyclic Ytterbium Complex

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