Large Optical Rotations Research Articles

Helical and Luminescent Disubstituted Polyacetylenes: Synthesis, Helicity, and Light Emission of Poly(diphenylacetylene)s Bearing Chiral Menthyl Pendant Groups

Diphenylacetylenes containing chiral menthyl groups [C6H5C≡C−C6H4OCOCH2OR* and C6H5C≡C−C6H4CO2R*, R* = (1R,2S,5R)-(−)-menthyl] are synthesized and polymerized by WCl6−Ph4Sn catalyst. The structures and properties of the polymers are characterized and evaluated by IR, NMR, TGA, UV, CD, and PL analyses. All the polymers are thermally stable, losing little of their weights when heated to ≥250 °C. They also enjoy high photostability, suffering no change in the molecular weight when exposed to UV irradiation in air for 24 h. The backbones of the polymers are induced to helically rotate by the chiral pendants, as verified by their large specific optical rotations and strong Cotton effects in the backbone absorption region in the solution and aggregate states. The polymers emit green light of 493 and 520 nm when their solutions and nanoparticle suspensions in poor solvents are photoexcited. UV irradiation of the polymer films in air photooxidizes the exposed regions, generating two-dimensional luminescent photop...

Enantioselective Adsorption of Chiral Amines on an Induced Helical Poly(bis(4-carboxyphenoxy)phosphazene): Chiral Filter Effect

Optically inactive poly((bis(4-carboxyphenoxy)phosphazene) (poly-1) showed a large optical rotation upon complexation with optically active (R)- or (S)-1-phenylethylamine (2) in DMSO after annealing the complex solution at 65 °C for ca. 2 h and maintained its optical activity in the presence of an equimolar amount of the opposite-handed 2. The detailed analysis of the enantiomeric excess of 2 adsorbed on the poly-1 revealed that the helical poly-1 induced by (R)- or (S)-2 most likely acts as a “chiral filter” to exclude one enantiomer from racemic 2, resulting in the retention of its induced helical structure.

Enhancement of optical birefringence in tellurite glasses containing silver nanoparticles induced via thermal poling

Wavelength-selective enhancement of optical birefringence has been observed in a tellurite glass containing silver nanoparticles (Ag NPs) induced via thermal poling. The birefringence appears as an optical rotation of linearly polarized light; a large optical rotation is observed at around the wavelength of localized surface plasmon resonance (LSPR) of Ag NPs. The optic axis is oriented along the electric field applied during the thermal poling, suggesting that birefringence induced in the glass matrix through the thermal poling is drastically enhanced by the NPs at around the LSPR. Because of the birefringence of the matrix, the wavelength of LSPR shifts depending on the polarization state of the incident light, which in turn induces the polarization dependence of the real part of the refractive index via the Kramers–Kronig relation.

Fast Electro-Optical Device Based on Chiral Liquid Crystals Encapsulated in Periodic Polymer Channels

The chiral flexo-electro-optic effect produces a sub-millisecond, temperature independent in-plane rotation of the optical axis and is potentially interesting for the display industry. The main drawback in the exploitation of this effect is that it relies on a texture, the Uniform Lying Helix (ULH), which is intrinsically unstable since neither planar nor homeotropic surface conditions are compatible with it. We present a method, based on the use of periodic polymeric micro-channels, to create highly ordered and stable ULH structures. We show that the periodic structure, which is created holographically, naturally aligns the cholesteric helical superstructure along the micro-channels, without requiring any elaborate ad-hoc procedure, even when the size Λ of the micro-channels is much larger than the pitch P (Λ > 20P). Electro-optic measurements performed on the test-device show a large contrast ratio between bright and dark states (better then 100:1), short switching time (200μs) and large optical rotation (>30°).

Synthesis and Secondary Structure of Poly(1-methylpropargyl-N-alkylcarbamate)s

A series of novel 1-methylpropargyl-N-alkylcarbamates, HC≡C-(R)-CH(CH3)OCONHCH2CO2CH2CH2CH3 [(R)-1], HC≡C-(S)-CH(CH3)OCONHCH2CO2CH2CH2CH3 [(S)-1], HC≡C-(S)-CH(CH3)OCONH-(R)-CH(CH3)CH2CH2CH2CH2CH3 [(S),(R)′-2], HC≡C-(S)-CH(CH3)OCONH-(R)-CH(CH3)CO2CH2CH2CH3 [(S),(R)′-3], HC≡CCH2OCONH-(R)-CH(CH3)CO2CH2CH2CH3 [(R)′-4], HC≡CCH2OCONH-(S)-CH(CH3)CO2CH2CH2CH3 [(S)′-4], and HC≡CCH2OCONHCH2CO2CH2CH2CH3 (5) were synthesized and polymerized using (nbd)Rh+[η6-C6H5B−(C6H5)3] (nbd = 2,5-norbornadiene) as a catalyst. Substituted cis-stereoregular polyacetylenes with moderate molecular weights were obtained in good yields. Poly[(R)-1], poly[(S)-1], poly[(S),(R)′-2], and poly[(S),(R)′-3] exhibited large optical rotations (|[α]D| = 344°−508°), clear CD signals (Δe = 4.8−7.0 M−1 cm−1) in CHCl3, and high viscosity indices (0.82−0.87), demonstrating the formation of helical structures with predominantly one-handed screw sense, which were stable up to 55 °C in the solvent. The solution state IR measurement confirmed the presenc...

Reflection spectra of NaClO3, NaBrO3, and LiIO3 gyrotropic crystals in the vacuum UV region

The reflection spectra in the fundamental-absorption region, 5–25 eV (250–40 nm), of optically active crystals with cubic symmetry (NaClO3, NaBrO3) and uniaxial optically active crystal (LiIO3) have been investigated. It is shown that the reflection spectra of cubic crystals have a similar structure, which is determined by the electronic transitions in the XO3 group. The comparison of these spectra with the corresponding spectrum of lithium iodide made it possible to determine the type of transition in the spectra of cubic crystals. Using the projection operator method, it was shown that the sign of optical rotation of cubic crystals with symmetry T is independent of the screw axis sign. Possible reasons for the unprecedentedy large optical rotation of lithium iodide crystal in the optical axis direction are considered.

Synthesis and Characterization of Poly(chiral methylpropargyl ester)s Carrying Azobenzene Moieties

AbstractNovel chiral methylpropargyl esters bearing azobenzene groups, namely, 4‐[4′‐(benzyloxy)phenylazophenyl]‐ carbonyl‐(S)‐1‐methylpropargyl ester (e), 4‐[4′‐(n‐butyloxy)phenylazophenyl]carbonyl‐(S)‐1‐methylpropargyl ester (f), 4‐[4′‐(n‐hexyloxy)phenylazophenyl]carbonyl‐(S)‐1‐methylpropargyl ester (g), and 4‐[4′‐(n‐octyloxy)phenylazo‐ phenyl]carbonyl‐(S)‐1‐methylpropargyl ester (h) were synthesized and polymerized with Rh+(nbd)[η6‐C6H5B−‐ (C6H5)3] (nbd=norbornadiene) catalyst to give the corresponding polymers with moderate molecular weights (Mn=8.4×103–15.7×103) in good yields (76%? –?91%). The structures of polymers were illustrated by IR and NMR spectroscopies. Polymers were soluble in comment organic solvents including toluene, CHCl3 CH2Cl2, THF, and DMSO, while insoluble in diethyl ether, n‐hexane and methanol. Large optical rotations of polymer solutions demonstrated that all the polymers take a helical structure with a predominantly one‐handed screw sense in organic solvents.

Chiroptically Active Photonics Polymers: Synthesis and Chiroptically Switching Properties of Helical Polyacetylene Bearing Electrochromic Viologens in the Side Chains

Toward near-infrared chiroptically active photonics polymers, a new type of optically active polyacetylene bearing l-alanine and electrochromic viologen in the side chains was prepared and carefully studied for the chiroptical properties. The resulting polymer exhibited much larger optical rotation ([m]25D = −1310°, DMF) than the model compound ([φ]25D = 201°, DMF) as well as a strong negative circular dichroism (CD) signal attributable to backbone absorption, indicating the formation of a single-handed helical structure of the polymer main chain. The content of viologen in the polymer was determined to be >70 mol % relative to the repeat unit by NMR and X-ray photoelectron spectrscopy. Because of the chiral perturbation of the helical main chain, the viologens in the side chains are asymmetrically positioned and interacted to yield a new strong negative CD band at long wavelengths (i.e., 450−800 nm) upon reduction to radical cations. The intensity of this CD signal could be easily switched between nearly...

Synthesis and photoisomerization of poly(1‐methylpropargyl ester)s carrying azobenzene moieties

AbstractOptically active 1‐methylpropargyl esters bearing azobenzene groups, namely, (S)‐(−)‐3‐methyl‐3‐{4‐[4‐(n‐butyloxy)phenylazophenyl]carbonyl}oxy‐1‐propyne (1), (S)‐(−)‐3‐methyl‐3‐{4‐[4‐(n‐hexyloxy)phenylazophenyl]carbonyl}oxy‐1‐propyne (2), and (S)‐(−)‐3‐methyl‐3‐{4‐[4‐(n‐octyloxy)phenylazophenyl]carbonyl}oxy‐1‐propyne (3) were synthesized and polymerized with Rh+(nbd)[η6‐C6H5B−(C6H5)3] (nbd, norbornadiene) as a catalyst to afford the corresponding poly(1‐methyloropargyl ester)s with moderate molecular weights (Mn = 24,000–31,300) in good yields (79–84%). Polymers were soluble in common organic solvents including toluene, CHCl3, CH2Cl2, THF, and DMSO, whereas insoluble in diethyl ether, n‐hexane, and methanol. Large optical rotations and strong CD signals demonstrated that all the polymers take a helical structure with a predominantly one‐handed screw sense. The helical structure of the polymers changed with the addition of MeOH and heat. The trans‐azobenzene of the polymer side chains isomerized into cis on UV irradiation, which was accompanied with drastic helical conformational changes of the polymer backbone. The cis‐azobenzene moiety reisomerized into trans on visible‐light irradiation, which induced the recovery of chiral geometry of azobenzene moieties in the side chain. Conformational analysis revealed that the polymers form a tightly twisted right‐handed helical structure with a dihedral angle of 70° at the single bond of the main chain. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4749–4761, 2009

Short pitch cholesteric electro-optical device based on periodic polymer structures

The helical flexoelectro-optic effect produces a submillisecond, temperature-independent in-plane rotation of the optical axis and is potentially interesting for the display industry. The main drawback is that it relies on a texture, the uniform lying helix (ULH), which is intrinsically unstable. We present a method based on the use of periodic polymeric microchannels to create highly ordered and stable ULH structures. Electro-optic measurements performed on a test device show a large contrast ratio between bright and dark states (better then 100:1), fast switching (200 μs), and large optical rotation (>30°).

Synthesis and Helical Structure of Poly(1‐methylpropargyl ester)s with Various Side Chains

Optically active 1-methylpropargyl esters bearing various substituents were polymerized with [(nbd)Rh](+)[eta(6)-C(6)H(5)B(C(6)H(5))(3)](-) (nbd=norbornadiene) as a catalyst to afford the corresponding poly(1-methylpropargyl ester)s with moderate molecular weights in good yields. The polymers have a cis-stereoregular structure, which was determined by (1)H NMR spectroscopy. Large optical rotations and clear CD signals demonstrated that all these polymers take on a helical structure with a predominantly one-handed screw sense. The polymers exhibited large viscosity indices in the range 1.14-1.75. Chiral amplification was observed in R/S copolymerization. Conformational analysis revealed that the polymers form a tightly twisted helical structure with a dihedral angle of 70 degrees at the single bond of the main chain.

A novel type of optically active helical polymers: Synthesis and characterization of poly(N‐propargylureas)

AbstractThis article presents two novel artificial helical polymers, substituted polyacetylenes with urea groups in side chains. Poly(4) and poly(5) can be obtained in high yields (≥97%) and with moderate molecular weights (11,000–14,000). Poly(4) contains chiral centers in side chains, and poly(5) is an achiral polymer. Both of the two polymers adopted helical structures under certain conditions. More interestingly, poly(4) exhibited large specific optical rotations, resulting from the predominant one‐handed screw sense. The helical conformation in poly(5) was stable against heat, while poly(4) underwent conformational transition from helix to random coil upon increasing temperature from 0 to 55 °C. Solvents had considerable influence on the stability of the helical conformation in poly(4). The screw sense adopted by the helices was also largely affected by the nature of the solvent. Poly(4‐co‐5)s formed helical conformation and showed large optical rotations, following the Sergeants and Soldiers rule. By comparing the present two polymers (with one NH groups) with the three polymers previously reported (with two NH groups in side chains), the nature of the hydrogen bonds formed between the neighboring urea groups played big roles in the formation of stable helical conformation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4112–4121, 2008

Synthesis of a series of soluble main-chain chiral nonracemic poly(alkyl-aryl ketone)

A series of main-chain chiral polyketones have been synthesized through condensation polymerization of a dihalide and a diketone with optically pure binaphthyl moiety as linkage in the polymer backbone. The solubility of the polymers can be easily enhanced by substituents at the alpha position next to the carbonyl groups. Reducing the steric hin- drance of the substituents in the monomers increases the reactivity of the polymerization. The chiral polymers exhibit large optical rotations. Circular Dichroism (CD) spectra of the polymers are similar to those of the corresponding monomers. The novel synthetic strategy may have great impact on future development of palladium catalyzed condensation polymeriza- tions. The highly soluble chiral polymers synthesized allow for preparation of materials in the form of thin films and have potentials applications in various areas such as chiral separation and recognition.

Enantioselective Synthesis of Binaphthyl Polymers Using Chiral Asymmetric Phenolic Coupling Catalysts: Oxidative Coupling and Tandem Glaser/Oxidative Coupling

A series of functionalized and optically active polybinaphthyls have been synthesized from achiral substrates by asymmetric oxidative phenolic coupling using a chiral 1,5-diaza-cis-decalin copper catalyst. In most cases, a copper tetrafluoroborate catalyst was found to be superior to the copper iodide catalyst, as ortho-iodination of the substrates could be prevented. Three methods for the formation of chiral polymers are described. In the first method, two 2-naphthols linked together at C-6 are subjected to the optimized asymmetric oxidative phenolic coupling conditions to form chiral polynaphthyls. A combination of NMR and HPLC measurements secured the selectivity of the asymmetric coupling. In the second method, substrates containing only one naphthalene were utilized. By incorporating a 2-naphthol and a terminal alkyne, the chiral copper catalysts effect both Glaser-Hay coupling of the alkyne and oxidative asymmetric coupling of the 2-naphthol with remarkable chemoselectivity. The relative reaction rates of various moieties with the chiral catalysts follows the order: benzyl cyanides > aryl alkynes > electron-rich 2-naphthols > electron-deficient 2-naphthols > alkyl alkynes. Because of high chemoselectivity, this approach is useful for the organized assembly of multifunctional substrates in a single operation. In all cases, no cross-coupling is observed between the alkyne and the 2-naphthol. This approach was thus applied to a set of highly functionalized precursors. In this third case, the biaryl coupling was performed first and a Glaser-Hay coupling was performed in a separate step to generate a highly functionalized polymer. In some cases, the resultant chiral polymers exhibit very large optical rotations.

Chiral 1-Methylpropargyl Alcohol: A Simple and Powerful Helical Source for Substituted Polyacetylenes

(S)- and (R)-1-methylpropargyl alcohols [(S)-1 and (R)-1] and their ester derivatives (S)- and (R)-1-methylpropargyl hexanoates [(S)-2 and (R)-2] were polymerized using (nbd)Rh+[η6-C6H5B-(C6H5)3] as catalyst to afford the corresponding substituted polyacetylenes with moderate molecular weights in good yields. The polymers possessed cis-stereoregular structures according to 1H NMR. Large optical rotations and clear CD signals demonstrated that these polymers took a helical structure with predominantly one-handed screw sense, stabilized by steric repulsion between the side chains containing chiral groups adjacent to the main chain.

Photoinduced Birefringence and Optical Rotation on Achiral Azobenzene Copolymer

Photoinduced birefringence and photoinduced optical rotation has been investigated on poly{4-[2-(methacryloyloxy)ethyloxy-4′-cyanoazobenzene]-co-4-[[2-(methacryloyloxy) ethyloxy]-2-methyl-4-(phenylazo)]azobenzene} (PCDY50). Originating in a good optical response of cyanoazobenzene side-chain and large birefringence of long π-conjugated side chains, a fairly large photoinduced birefringence (0.28) and photoinduced optical rotation (41°/μm) could be observed. Some applications utilizing these superior photoresponsive properties of PCDY50 have been suggested and demonstrated.

Photoinduced Molecular Re-orientation and Supramolecular Helical Structure Formation in Azobenzene Materials

ABSTRACT Photoinduced chirality in azobenzenes has been investigated. Even in low-molecular weight azobenzenes, photoinduced optical rotation could be observed and the characteristics were similar to that of ever reported in azobenzene side-chain-type polymer. Any relationship between molecular chirality and photoinduced chirality could not be observed in low-molecular weight azobenzenes. Further, very large optical rotation of 41 deg./μm could be observed in an azobenzene copolymer containing large birefringent unit. Dependence of optical rotation on intensity, wavelength and ellipticity of excitation beam were examined. The phenomenon was discussed based on the assumption that photoinduced helical structure was formed by elliptically polarized beam irradiation.

Synthesis and evaluation of new chiral nonracemic C2-symmetric and unsymmetric 2,2′-bipyridyl ligands

The synthesis of a series of chiral nonracemic and C2-symmetric 2,2'-bipyridyl ligands (R = Me, i-Pr and Ph) as well as the syntheses of the corresponding unsymmetric 2,2'-bipyridyl ligands (R = Me and Ph) is described. These bipyridyl ligands were prepared, in a notably direct and modular fashion, from the readily available and corresponding 2-chloropyridine acetals (R = Me, i-Pr and Ph). The bipyridyl ligands were evaluated in copper(I)-catalyzed cyclopropanation reactions of styrene with the ethyl and t-butyl esters of diazoacetic acid. The stereoselectivities, as well as the yields of the cyclopropanation reactions, were dependant on the ratio of the bipyridyl ligands and copper triflate that was employed. The best result was obtained in the asymmetric cyclopropanation reaction of styrene and tert-butyl diazoacetate with the C2-symmetric bipyridyl ligand (R = i-Pr). This afforded the corresponding trans-cyclopropane in good diastereoselectivity (4 : 1) and in moderate enantioselectivity (44% ee). The X-ray structure determination of a complex formed between the C2-symmetric 2,2'-bipyridyl ligand (R = Ph) and copper(I) chloride showed that two bipyridyl ligands had coordinated to the copper(I) ion. This information, along with the results of a series of cyclopropanation reactions and NMR data, led to the conclusion that the 2,2'-bipyridyl ligands had the propensity to form catalytically inactive bis-ligated copper(I) species in solution that were in equilibrium with catalytically active copper(i) triflate and the desired mono-ligated copper(I) species. Moreover, it was observed that the complex of the bipyridyl ligand (R = Ph) and copper(I) chloride had a particularly large optical rotation (sodium D-line). The maximum positive optical rotation was subsequently found to be +1.1 x 10(4) at 304 nm and the maximum negative optical rotation was -1.3 x 10(4) at 329 nm.

Photoinduced Chirality in an Azobenzene Amorphous Copolymer Bearing Large Birefringent Moiety

A photoresponsive amorphous copolymer that consists of cyanoazobenzene and a large birefringent moiety with extended π-conjugation was recently designed and synthesized. It has been confirmed that this copolymer exhibits a very large optical rotation of 41°/µm under the optimized excitation conditions practically determined within our optical setup, i.e., 457.9 nm, 30 mW and ellipticity=-0.5. The large rotation angle observed could be attributed to the increment of the order parameter of the polymer side chains promoted by the introduction of the extended π-conjugated moiety. Even more, the dependence of optical rotation on beam power, wavelength and ellipticity of the excitation beam has been examined. The phenomenon of photoinduced chirality in an azobenzene amorphous copolymer is discussed and analyzed on the basis of general ellipsometry by solving the transformation matrix of the sample.

Control of Helix Sense by Composition of Chiral–Achiral Copolymers of N‐Propargylbenzamides

N-Propargylbenzamides 1-7 were polymerized with (nbd)Rh(+)[eta(6)-C(6)H(5)B(-)(C(6)H(5))(3)] to afford polymers with moderate molecular weights (M(n) = 26,000-51,000) in good yields. The (1)H NMR spectra demonstrated that the polymers have fairly stereoregular structures (81-88 % cis). The optically active polymers, poly(1) and poly(2), were proven by their intense CD signals and large optical rotations to adopt a stable helical conformation with an excess of one-handed screw sense when heated in CHCl(3) or toluene. The sign of Cotton effect could be controlled by varying the content in the copolymers of either chiral bulky 1 and achiral nonbulky 3, or chiral nonbulky 2 and achiral bulky 7. The smaller the pendant group in the copolymerization of achiral monomers with 1, the more easily did the preferential helical sense change with the copolymer composition. However, the copolymers of chiral nonbulky 2 and achiral nonbulky 3 did not change the helical sense, irrespective of the composition. The free energy differences between the plus and minus helical states, as well as the excess free energy of the helix reversal, of those chiral-achiral random copolymers were estimated by applying a modified Ising model.