Stable helical polyguanidines: poly[N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]guanidines

Using chiral catalysts of (R)- and/or (S)-BINOL-Ti, the asymmetrical polymerization of achiral monomer, N-(1-anthryl)-N'-n-octadecylcarbodiimide, yielded soluble nonregioregular polyguanidines of Poly-R1 and Poly-S1. A racemization process occurred when the toluene solution of Poly-R1 was annealed at elevated temperatures (70-80 degrees C). Kinetic studies reveal this to be a slow process with an activation energy of ca. 36 kcal/mol. On the other hand, using titanium(IV) trifluoroethoxide catalyst, the polymerization of N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]carbodiimides afforded highly regioregular polyguanidines of Poly-R2 and Poly-S2. These polymers adopt stable helices in various solvents and elevated temperatures, whose kinetically controlled conformations and thermodynamically controlled conformations are essentially the same.     

含手性亚胺侧基聚苯乙烯衍生物的设计及其在酸碱诱导下的手光响应性质

以N-(2-羟基-1-萘基)亚甲基-(S)-α-苯基乙胺为模型分子,考察了脱质子前后该手性Schiff碱溶液手光性质的变化,利用DFT计算探讨手光信号反转机理.结果表明,手光反转源于分子内氢键的断裂与形成及伴随的C—C单键旋转所引起的构象转变,且前后2种构象处于拟对映关系.这一发现意味着通过单键旋转操控分子构象转变可作为构建手性开关的一种有效途径.在此基础上设计、合成了苯乙烯型手性功能单体(VNP)及相应的光学活性聚合物.由于邻位基团的协同效应,聚合物的手光性质对酸碱刺激表现出比单体更灵敏的响应性和可重复性.当循环加入H+和OH-时,聚合物溶液的CD信号(382 nm处的Cotton效应)以"ON"-"OFF"方式发生可逆转变,以此为输出信号可无损耗重复至少5次,实现了通过酸碱调控的无损输出的新型聚合物基手性开关.此外,基于该手性开关体系构建了典型的"禁阻"(IHIBIT)分子逻辑门.     

PHOTOPHYSICS and PHOTOCHEMISTRY OF BIS-2-(9-ANTHRYL)ETHYL GLUTARATE

Abstract— The photochemistry and photophysics of bis-(2-(9-anthryl)ethyl glutarate 2 and 2-(9-anthryl) ethyl pivalate 3 have been examined as monomeric models for poly-2-(9-anthryl)ethyl methacrylate 1. The absorption and excitation spectra of 2 show no ground state interaction, but appreciable monomer (51%) and excimer (49%) emission. Delayed monomer and excimer fluorescence are also observed in fluid solution at room temperature. Photolysis of 2 at low temperature produces a photoproduct (44% yield) which is unstable at room temperature and presumably is the head-to-head (H-H) dimer. Steady state irradiation of 2 at room temperature (Λ 350 nm) cleanly produces a head-to-tail (H-T) dimer (6) derived from the singlet state and an additional unidentified adduct (7). The product distribution is concentration dependent, with 6 predominating at high concentrations (> 10⁻³ M ). The fluorescence spectra of the broken dimers derived from 6 and 7 indicate that substantial ir overlap exists in the transition state leading to each product.     

Solvent‐Induced Helical Assembly and Reversible Chiroptical Switching of Chiral Cyclic‐Dipeptide‐Functionalized Naphthalenediimides

Understanding the roles of various parameters in orchestrating the preferential chiral molecular organization in supramolecular self‐assembly processes is of great significance in designing novel molecular functional systems. Cyclic dipeptide (CDP) chiral auxiliary‐functionalized naphthalenediimides (NCDPs 1 – 6 ) have been prepared and their chiral self‐assembly properties have been investigated. Detailed photophysical and circular dichroism (CD) studies have unveiled the crucial role of the solvent in the chiral aggregation of these NCDPs. NCDPs 1 – 3 form supramolecular helical assemblies and exhibit remarkable chiroptical switching behaviour (M‐ to P‐type) depending on the solvent composition of HFIP and DMSO. The strong influence of solvent composition on the supramolecular chirality of NCDPs has been further corroborated by concentration and solid‐state thin‐film CD studies. The chiroptical switching between supramolecular aggregates of opposite helicity (M and P) has been found to be reversible, and can be achieved through cycles of solvent removal and redissolution in solvent mixtures of specific composition. The control molecular systems (NCDPs 4 – 6 ), with an achiral or D ‐isomer second amino acid in the CDP auxiliary, did not show chiral aggregation properties. The substantial roles of hydrogen bonding and π–π interactions in the assembly of the NCDPs have been validated through nuclear magnetic resonance (NMR), photophysical, and computational studies. Quantum chemical calculations at the ab initio, semiempirical, and density functional theory levels have been performed on model systems to understand the stabilities of the right (P‐) and left (M‐) handed helical supramolecular assemblies and the nature of the intermolecular interactions. This study emphasizes the role of CDP chiral auxiliaries on the solvent‐induced helical assembly and reversible chiroptical switching of naphthalenediimides.     

ORD and CD studies of poly[(S)(−)-N-α-methylbenzylethylenimine]

The advantages of chiral N-substituted polyethylenimines for the chiroptical study of macromolecular conformations in solution have been considered. Poly[(S)(?)-N-α-methylbenzylethylenimine] (poly-3) and five model compounds have been obtained and their chiroptical properties studied. The cyclic dimer and tetramer of imine 3 are suitable models for the chiroptical study of configurational and conformational behaviour of randomly coiled and helical poly-3 in solution. Unlike the disordered poly-3 in acidified solvents and the configurational models in various solvents, helical poly-3 in hydrocarbon solvents has positive optical rotation and positive CD-band of the tertiary amine chromophore at 223 nm. The appearance of this inherently chiral chromophore of the helix explains the observed changes of the sign and values of the optical rotation of poly-3 in various solvents which are mainly caused by conformational transformations of the main chain. The presence of helical conformations of poly-3 in solution are also confirmed by optical rotation data of stereocopolymers and the concentration dependence data of ORD curves of poly-3. This conclusion agrees with NMR and i.r.-data.     

Reversible CO2-, Photo- and Thermo- Triple Responsive Supramolecular Chirality of Azo-containing Block Copolymer Assemblies Prepared by Polymerization-induced Chiral Self-assembly

Polymerization-induced chiral self-assembly(PICSA)is an efficient strategy that not only allows the construction of the supramolecular chiral assemblies in a controlled manner but also can regulate the morphology in situ.Herein,a series of azobenzene-containing block copolymer(Azo-BCP)assemblies with tunable morphologies and supramolecular chirality were obtained through the PICSA strategy.The supramolecular chirality of Azo-BCP assemblies could be regulated by carbon dioxide(CO₂)stimulus,and completely recovered by bubbling with Ar.A reversible morphology transformation and chiroptical switching process could also be achieved by the alternative 365 nm UV light irradiation and heatingcooling treatment.Moreover,the supramolecular chirality is thermo-responsive and a reversible chiral-achiral switching was successfully realized,which can be reversibly repeated for at least five times.This work provides a feasible strategy for constructing triple stimuli-responsive supramolecular chiral nano-objects in situ.     

Supra‐dendron Gelator Based on Azobenzene–Cyclodextrin Host–Guest Interactions: Photoswitched Optical and Chiroptical Reversibility

A novel amphiphilic dendron ( AZOC₈GAc ) with three l ‐glutamic acid units and an azobenzene moiety covalently linked by an alkyl spacer has been designed. The compound formed hydrogels with water at very low concentration and self‐assembled into chiral‐twist structures. The gel showed a reversible macroscopic volume phase transition in response to pH variations and photo‐irradiation. During the photo‐triggered changes, although the gel showed complete reversibility in its optical absorptions, only an incomplete chiroptical property change was achieved. On the other hand, the dendron could form a 1:1 inclusion complex through a host–guest interaction with α‐cyclodextrin (α‐CD), designated as supra‐dendron gelator AZOC₈GAc/α‐CD . The supra‐dendron showed similar gelation behavior to that of AZOC₈GAc , but with enhanced photoisomerization‐transition efficiency and chiroptical switching capacity, which was completely reversible in terms of both optical and chiroptical performances. The self‐assembly of the supra‐dendron is a hierarchical or multi‐supramolecular self‐assembling process. This work has clearly illustrated that the hierarchical and multi‐supramolecular self‐assembling system endows the supramolecular nanostructures or materials with superior reversible optical and chiroptical switching.     

Synthesis and chiroptical properties of optically active poly(N‐propargylamide) bearing photoisomerizable azobenzene moieties

A chiral azobenzene‐containing N‐propargylamide monomer, that is, (R)‐2‐(4‐phenylazophenoxy)‐n‐prop‐2‐ynyl‐propionamide, was prepared and polymerized in the presence of a rhodium catalyst to yield an optically active polyacetylene. The ¹H NMR analysis of the polymer indicated a predominant cis structure of the backbone (cis concentration = 80%); and the chiroptical property studies showed an enhanced optical rotatory power and a strong Cotton effect, indicating the formation of a secondary helical conformation. A reversible optical modulation of chiroptical properties of the polymer due to the reversible photoisomerization of the azobenzene was observed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6047–6054, 2006     

TDDFT studies on chiral organophosphonate substituted divacant Keggin-type polyoxotungstate: diplex multistep-redox-triggered chiroptical and NLO switch

We theoretically investigate a novel switching phenomenon based on the divacant Keggin-type polyoxotungstate bearing chiral organophosphonate [{NH(2)CH(CH(3))PO}(2)(γ-SiW(10)O(36))](4-), that is the synchronous chiroptical and nonlinear optical (NLO) switch triggered by redox. The ECD calculations on the Boltzmann weighted conformations of the three oxidation states of this chiral polyoxometalate (POM) clearly present a chiroptical switching process. The electronic transition and the bond-length alternation studies show that the chirality transfer from chiral carbon atom to POM cage increases as the polyanion is reduced. Simultaneously, the static first hyperpolarizability of studied chiral POM quadrupled from the oxidized state to the 1e-reduced state, and is further doubled to the 2e-reduced state, which is mainly due to the increasing electronic-dipole-allowed d-d charge transfer transitions in the POM cage. This work firstly reproduces the ECD spectrum of chiral POM with high accuracy and proves the possibility for confirming the molecular conformations of flexible chiral POMs in solution by the aid of ECD calculations. Most importantly, a sensitive diplex switch based on a chiral POM is predicted in theory, which may aid the design of novel POM-based switches.     

Macromolecular helicity induction on a poly(phenylacetylene) with C2-symmetric chiral [60]fullerene-bisadducts

Three chiral N-methylfulleropyrrolidine bisadducts were prepared, isolated, and completely resolved into each enantiomer using a chiral HPLC column, which were then converted to the corresponding optically active, cationic C(60)-bisadducts to investigate if they could act as a macromolecular helicity inducer in a poly(phenylacetylene) bearing an anionic monoethyl phosphonate pendant (poly-1) in aqueous solution. Upon complexation with the chiral C(60)-bisadducts, only the trans-3 bisadduct exhibited the characteristic induced circular dichroism (ICD) in the UV-visible region of the polymer backbone in dimethyl sulfoxide-water mixtures due to the predominantly one-handed helix formation of poly-1, while the trans-2 and cis-3 bisadducts induced almost no apparent CD in the same region. These results indicate that the helicity induction on poly-1 is highly sensitive to the structure and geometry of the cationic C(60)-bisadducts with a different distance between the separated charges.     

基于电致酸/碱理论的手性光学切换体系

手性分子光学开关在光学储存、 光学通信以及三维立体显示等领域有着重要的应用价值. 但是目前的手性分子光学开关存在材料种类少、 光学可调性差、 稳定性差等缺点, 如何构筑出具有高光学可调性以及稳定性的手性光学切换体系依旧是一项严峻的挑战. 本工作基于电致酸/碱理论, 通过将手性联萘官能团引入到酸响应的罗丹明主体结构中, 设计并合成了一种新型的酸响应手性光学开关分子, 并将其与电致酸材料相结合, 成功实现了电场驱动的手性光学开关过程, 开发了一种新型的手性光学切换体系. 发现在合适的电场控制下, 其颜色、 荧光以及圆二色谱信号均能发生可逆的变化. 这种方法为构筑新型手性光学开关体系提供了一种新思路, 对手性光学开关材料的应用拓展具有重要的参考价值.     

Thermal and light control of the chiral order of azopolymers

The control of the chiroptical properties of two azopolymers, which contain chiral terminal alkyl chains, by means of thermal and light irradiation processes has been studied. Both UV–vis and CD spectra of films and dichloromethane (DCM)/hexane solutions of the polymers have been registered and analyzed before and after different irradiation conditions: 488 nm circularly polarized light (CPL) and 365 nm unpolarized light. The chiroptical properties of the polymer containing chiral 1-methylheptyloxy terminal chains depended on the thermal history of the sample. As a result, the photocontrol of the chiral response in the bulk material by CPL irradiation has been evaluated on samples cooled from the isotropic state to room temperature at different rates. The chiroptical properties of these azopolymers show an intriguing combination of control from both the supramolecular and molecular chirality level as well as the thermal history of the sample and CPL irradiation.     

Electron-induced switching of the supramolecular chirality of optically active polythiophene aggregates

A chiral regioregular polythiophene (PT), poly[3-[4-((R)-4-ethyl-2-oxazolin-2-yl)phenyl]thiophene] (poly-1), forms chiral aggregates which exhibit a unique induced circular dichroism (ICD) in the pi-pi transition region derived from the supramolecular chirality in the presence of various poor solvents or metal salts in chloroform. We report here that the chirality of such supramolecular aggregates can be switched ("on" and "off") through electron transfer. We have found that upon the addition of copper(II) trifluoromethanesulfonate [Cu(OTf)(2)] to the chiral aggregates of poly-1 in a chloroform-acetonitrile mixture, the ICD disappears because of the oxidative doping of the poly-1 main chain, while a further addition of amines such as triethylenetetramine (TETA) induces undoping of the poly-1 which results in the reappearance of the ICDs. Therefore, the supramolecular chirality of the poly-1 assemblies was reversibly controlled by the addition or removal of an electron from the poly-1 main chain. This may be the first example of a reversible supramolecular chirality switch on chiral PT aggregates. We investigated the mechanism of the chirality switch through the doping and undoping process on the polymer main chain by means of absorption and CD spectroscopies, ESR, cyclic voltammetry, X-ray diffraction, and AFM measurements.     

Surface reconstruction of chiral glassy oligomers under the action of volatile organic compounds (VOCs)

The response of chiral polymers to volatile organic compounds (VOCs) was studied by atomic force microscopy. It was found that under the influence of toluene vapour, the focal conic domains on the surface of chiral polymer undergo remarkable reconstruction that is at least partially reversible. This opens new ways for building VOC sensors and using surface reconstruction in creating new surface patterns for nanotechnology.     

Redox‐Triggered Chirality Switching and Guest‐Capture/Release with a Pillar[6]arene‐Based Molecular Universal Joint

A chiral electrochemically responsive molecular universal joint (EMUJ) was synthesized by fusing a macrocyclic pillar[6]arene (P[6]) to a ferrocene‐based side ring. A single crystal of an enantiopure EMUJ was successfully obtained, which allowed, for the first time, the definitive correlation between the absolute configuration and the circular dichroism spectrum of a P[6] derivative to be determined. The self‐inclusion and self‐exclusion conformational change of the EMUJ led to a chiroptical inversion of the P[6] moiety, which could be manipulated by both solvents and changes in temperature. The EMUJ also displayed a unique redox‐triggered reversible in/out conformational switching, corresponding to an occupation/voidance switching of the P[6] cavity, respectively. This phenomenon is an unprecedented electrochemical manipulation of the capture and release of guest molecules by supramolecular hosts.     

Redox-Triggered Chirality Switching and Guest-Capture/Release with a Pillar[6]arene-Based Molecular Universal Joint

A chiral electrochemically responsive molecular universal joint (EMUJ) was synthesized by fusing a macrocyclic pillar[6]arene (P[6]) to a ferrocene-based side ring. A single crystal of an enantiopure EMUJ was successfully obtained, which allowed, for the first time, the definitive correlation between the absolute configuration and the circular dichroism spectrum of a P[6] derivative to be determined. The self-inclusion and self-exclusion conformational change of the EMUJ led to a chiroptical inversion of the P[6] moiety, which could be manipulated by both solvents and changes in temperature. The EMUJ also displayed a unique redox-triggered reversible in/out conformational switching, corresponding to an occupation/voidance switching of the P[6] cavity, respectively. This phenomenon is an unprecedented electrochemical manipulation of the capture and release of guest molecules by supramolecular hosts.     

Macromolecular helicity inversion of poly(phenylacetylene) derivatives induced by various external stimuli

Unique macromolecular helicity inversion of stereoregular, optically active poly(phenylacetylene) derivatives induced by external achiral and chiral stimuli is briefly reviewed. Stereoregular, cis-transoidal poly(phenylacetylene)s bearing an optically active substituent, such as (1R,2S)-norephedrine (poly- 1 ) and β-cyclodextrin residues (poly- 2 ), show an induced circular dichroism (ICD) in the UV-visible region of the polymer backbone in solution due to a predominantly one-handed helical conformation of the polymers. However, poly- 1 undergoes a helix-helix transition upon complexation with chiral acids having an R configuration, and the complexes exhibit a dramatic change in the ICD of poly- 1 . Poly- 2 also shows the inversion of macromolecular helicity responding to molecular and chiral recognition events that occurred at the remote cyclodextrin residues from the polymer backbone; the helicity inversion is accompanied by a visible color change. A similar helix-helix transition of poly((R)- or (S)-(4-((1-(1-naphthyl)ethyl)carbamoyl)phenyl)acetylene) is also briefly described.     

Electrical bistability and memory phenomenon in carbon nanotube-conjugated polymer matrixes

We have observed electrical bistability and large conductance switching in functionalized carbon nanotube (CNT)-conjugated polymer composites at room temperature. The concentration of the CNTs in the polymer matrix controlled the degree of bistability. Conduction mechanism applicable in each of the conducting states has been identified. The switching had an associated memory phenomenon and was reversible in nature. In the bistable devices, the active layer retained its high-conducting state until a reverse voltage erased it. We could "write" or "erase" a state and "read" it for many cycles for random-access memory applications.     

Functionality and structure of polymers. I. Photoreaction and fluorescence of polyesters having pendant anthryl groups

Various polyesters having pendant (9-anthryl)methyl groups were prepared from 2-(9-anthryl)methylpropane-1,3-diol and the esters or chlorides of dicarboxylic acids. These polyesters are poly[2-(9-anthryl)-methylpropane-1,3-diyl-oxy-(9-anthryl)methylmalonyl-oxy](PA-1A), poly-[2-9-anthrylmethylpropane-1,3-diyl-oxysuccinyloxy](PA-2), poly-[2-9-anthrylmethylpropane-1,3-diyl-oxyadipyloxy](PA-4), poly[2-(9-anthryl)methylpropane-1,3-diyl-oxysebacyloxy] (PA-8), poly[2-(9-anthryl)methylpropane-1,3-diyl-oxy-(1-naphthyl)methylmalonyloxy](PA-1N), and poly[2-(9-anthryl)methylpropane-1,3-diyl-oxyterephthaloyloxy](PA-Ph). Although the absorption spectrum of the anthryl group is not influenced by the change in the environment in which the anthryl group is located, the fluorescence spectra show characteristic change reflecting the environment around the chromophore. Dimer, aggregates, or excimer fluorescence of anthryl groups and energy transfer from naphthyl to anthryl groups for PA-1N were discussed. The rates of photodimerization of anthryl groups determined spectroscopically in dilute solutions for these polyesters and their monomer model compound(1,3-diacetoxy-2(9-anthryl)methylpropane) (MA), were in the following order; PA-8 > PA-4 > PA-1A > PA-2 > PA-Ph > MA. The effects of polymer structure on the photoreaction were discussed on the basis of information on molecular interactions obtained by fluorescence spectroscopy. The fraction of intramolecular cyclization was estimated from dependence of the rate of photoreaction on the concentration of the polyesters. When anthryl groups are linked by a long, flexible polymethylene chain (PA-8), intramolecular process predominates whereas intermolecular dimerization proceeds almost exclusively for a rodlike molecule(PA-Ph). These results are discussed from the viewpoint of the structure–functionality relationship in polymeric systems.     

Construction of Chiroptical Switch on Silica Nanoparticle Surface via Chiral Self-assembly of Side-chain Azobenzene-containing Polymer

In this contribution, we utilized surface-initiated atom transfer radical polymerization(SI-ATRP) to prepare organic-inorganic hybrid core/shell silica nanoparticles(NPs), where silica particles acted as cores and polymeric shells(PAzo MA*) were attached to silica particles via covalent bond. Subsequently, chiroptical switch was successfully constructed on silica NPs surface taking advantage of supramolecular chiral selfassembly of the grafted side-chain Azo-containing polymer(PAzo MA*). We foun...