Molecular switches controlled by light

The photochemical processes of singlet-singlet energy transfer and photoinduced electron transfer are important not only in natural and artificial photosynthetic energy conversion, but also in a variety of other scientific and technological applications. Controlling these functions at the molecular level using outside stimuli is an interesting scientific challenge. Photochromes, organic molecules that are isomerized by light between two stable forms, can be covalently linked to other chromophores, and changes in their properties resulting from photoisomerization used to switch electron and energy transfer on or off. Simple single- and double-throw molecular switches have been constructed, as well as Boolean logic gates. Such molecules are potentially useful in light-controlled molecular data processing and storage applications.     

氧化偶联共聚合制备主链含β-萘烷基醚的红色发光聚合物

用氧化偶联聚合法合成了主链上含β-萘烷基醚和吡啶、二烷基芴、二苯乙烯和均四甲苯的聚合物.用FT-IR和1H NMR表征了聚合物的结构.广角X射线衍射表明共聚物的结构都是非晶态的.用UV-V is表征了共聚物的吸收特征.聚合物的荧光光谱表明,含有β-萘烷基醚和吡啶的聚合物在溶液中表现为红光发射材料.含有β-萘甲醚和二苯乙烯的共聚物为黄橙光发射,通过改变单体含量也可实现红光发射.含有β-萘甲醚和二烷基芴的聚合物固体有望成为白光发射材料.     

Design,synthesis, photophysical,and electrochemical properties of DCM‐based conjugated polymers for light‐emitting devices

A series of conjugated hyperbranched polymers, hyperbranched copolymers, and linear polymers containing 2‐pyran‐4‐ylidenemalononitrile (acceptor) and triphenylamine/fluorene (donor) units were synthesized and characterized by FTIR, ¹H NMR, thermogravimetric analyses, differential scanning calorimetry, gel permeation chromatography, UV–visible, photoluminescence, and cyclic voltammetry measurements. All the polymers show red‐light emission in the range of 566–656 nm both in solution and in solid state. The quantum efficiency of the polymers was in the range of 56–82%. Among the six polymers synthesized, only polymers containing fluorene units show T_g and polymers based on triphenylamine not exhibit T_g. The band gap of these polymers were found to be reasonably low; hyperbranched copolymer containing fluorene unit shows lowest band gap of 2.18 eV due to the stabilization of LUMO energy level by the electron withdrawing ? CN groups. The thermal and solubility behavior of the polymers were found to be good. All the EL spectra of the devices (indium‐tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)/polymer/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline/tris(8‐hydroxyquinoline)aluminum)/LiF/Al) show red‐light emission, and the device fabricated with P3 and P4 shows maximum luminance and luminous efficiency of 4104 cd m^?2 and 0.55 cd Å^?1 and 3696 cd m^?2 and 0.47 cd Å^?1, respectively, indicates that they had the best carrier balance. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Smart functionalized thin gel layers for electrochemical sensors,biosensors and devices

Combining hydrogels sensitive to external stimuli with conducting surfaces opens new possibilities in electrochemistry. Thin hydrogel layers as unique electrode-modifying materials provide highly permeable matrix for easy diffusion of analytes. In addition, larger individuals, for example, nanoparticles and enzymes, can be straightforwardly immobilized in the polymeric networks at electrode surfaces. Such properties are strongly desired for construction of sensors and biosensors. In addition, sensitivity to external stimuli allows to significantly enhance or weaken the electroanalytical signal. Recently, a significant number of articles concerning switchable sensors/biosensors, switchable electrochemical systems and signal–responsive interfaces have been published. This report is also focused on the construction of various devices based on electrode surfaces modified with smart hydrogel layers, for example, logic gates and electroresponsive hydrogel layers as potentially advanced drug delivery systems, artificial muscles and electrochemical valves.     

Nitrate and chloride transport through a smart membrane

To develop membranes having ionic selective properties under control of external stimuli is a challenge of the membrane and material scientific community. Conducting polymers swell and shrink under electrochemical control, so they are good candidates to prepare such smart membranes. The ionic transport through a new free-standing polypyrrole film working as a membrane in a diffusion cell was studied. The driving forces were transversal electric fields or concentration gradients across the film. The obtained ionic conductivity was dependent on both the electrolyte nature and concentration, as well as on the oxidation degree of the film, which was controlled by the applied external electric potential. Reverse and continuous changes of up to one order of magnitude on the transversal ionic conductivity are obtained when the membrane is in stationary oxidation states attained by polarisations at a constant potential in the range between −0.6 V and +0.4 V, respectively. A prevalent conductivity of anions (t₋ = 0.94) was obtained from Donnan potential measurements. The experimental results indicate that the oxidised film behaves as a nanoporous membrane highly permeable to nitrate ions, while the rejection of these ions is very high in the reduced film. The free-standing polypyrrole film works then as a smart membrane selective to nitrate ions under concentration gradient.     

芴-噁二唑类聚合物的合成及光谱特性

通过缩聚反应,制得了高分子量的线型和超支化的芴-噁二唑类聚合物．它们均可溶于常用的有机溶剂。在固态薄膜时,它们的紫外-可见光吸收光谱在大约398nm和376nm处有两个强的吸收峰。它们的薄膜PL光谱在蓝光波长范围内有强发射峰,薄膜PL效率约为16％。电化学测试显示它们的的LUMO能级比芴的均聚物高,而与钙、镁这样典型的阴极材料的功函数较接近．这表明此类聚合物具有较好的电子注入和传输性能。     

Reversible Phase Transition of Porous Coordination Polymers

Porous coordination polymers or metal–organic frameworks with reversible phase-transition behavior possess some attractive properties, and can respond to external stimuli, including physical and chemical stimuli, in a dynamic fashion. Their phase transitions can be triggered by adsorption/desorption of guest molecules, temperature changes, high pressure, light irradiation, and electric fields; these mainly include two types of transitions: crystal–amorphous and crystal–crystal transitions. These types of porous coordination polymers have received much attention because of their interesting properties and potential applications. Herein, reversible phase transition porous coordination polymers are summarized and classified based on different stimuli sources. Corresponding typical examples are then introduced. Finally, examples of their applications in gas separation, chemical sensors, guest molecule encapsulation, and energy storage are also presented.     

pi-Conjugated chelating polymers with charged iridium complexes in the backbones: synthesis, characterization, energy transfer, and electrochemical properties

A series of pi-conjugated chelating polymers with charged iridium (Ir) complexes in the backbones were synthesized by a Suzuki polycondensation reaction, leading to homogeneous polymeric materials that phosphoresce red light. The fluorene and bipyridine (bpy) segments were used as polymer backbones. 5,5'-Dibromobipyridine served as a ligand to form a charged iridium complex monomer with 1-(9'9-dioctylfluorene-2-yl)isoquinoline (Fiq) as the cyclometalated ligand. Chemical and photophysical characterization confirmed that Ir complexes were incorporated into the backbones as one of the repeat units by means of the 5,5'-dibromobipyridine ligand. Chelating polymers showed almost complete energy transfer from the host fluorene segments to the guest Ir complexes in the solid state when the feed ratio was 2 mol %. In the films of the corresponding blend system, however, energy transfer was not complete even when the content of Ir complexes was as high as 16 mol %. Both intra- and intermolecular energy-transfer processes existed in this host-guest system, and the intramolecular energy transfer was a more efficient process. All chelating polymers displayed good thermal stability, redox reversibility, and film formation. These chelating polymers also showed more efficient energy transfer than the corresponding blended system and the mechanism of incorporation of the charged Ir complexes into the pi-conjugated polymer backbones efficiently avoided the intrinsic problems associated with the blend system, thus offering promise in optoelectronic applications.     

Fluorescent aromatic polyamides with urea binding sites and fluorene or dansyl signaling units

This work describes six novel fluorescent aromatic polyamides with bulky dansyl or fluorene pendant groups or with the fluorene moiety in the main chain. The fluorescent signaling dansyl or fluorene moieties are chemically connected to, or within, the main polymer chains through a urea group, a well-known binding site in supramolecular chemistry. These polyamides are amorphous and soluble in polar aprotic solvents and demonstrate a film-forming capability. They also show yellowish-green or blue fluorescence in solution and in the solid state depending on the signaling unit, with the former corresponding to the dansyl and the latter to the fluorene residue. The water uptake and the thermal behavior have also been evaluated and related to the chemical structure. The polar amide, urea, and sulfonamide groups give rise to a high water sorption of up to 3.8 water molecules per repeating unit. The thermal behavior has been investigated by means of DSC and TGA. The glass transition temperatures of the polymers are high (up to 331 °C) and the decomposition temperatures (around 300 °C) are due to the moderate thermal stability of the urea group.     

Novel Efficient Light-Emitting Polyfluorene Derivatives Modified by Electron-Deficient Moieties with Nonlinear Structure

Two novel fluorene-based copolymers (PFSD and PFMD) containing squaric acid or maleimide unit in the main chain were synthesized in good yields by Suzuki coupling reaction. The resulting polymers possess excellent thermal stability, high electron affinity and high photolurninescence (PL) quantum yields. They can fluoresce in yellow-light range due to either the charge transfer between a fluorene segment and an electron-deficient containing squaric acid/maleimide segment of the polymers or the Forrster energy transfer between different polymer chains.The results from PL measurements of the isothermally heated polymer thin films show that the commonly observed aggregate excimer formation in polyfluorenes is very effectively suppressed in these two polymers due to the nonlinear structures of maleimide and squaric acid moieties. Double-layer polymer light-emitting diodes (PLED) were fabricated using the resulting polymers as the emitting layers and Ba or Mg：Ag(V：V=10：1) as cathodes.All the devices show bright yellow emission (562-579nm) with different maximum external quantum efficiencies (0.006%-1.13%). Compared with the other devices, indium-tin oxide (ITO)/polyethylenedioxythiophene (PEDOT):polystyrene sulfonic acid (PSS)/PFMD/Mg:Ag has the higher maximum external quantum efficiency of 1.13% at 564cd/m^2 with a bias of 8.4V.     

DNA-Based Adaptive Plasmonic Logic Gates

Self-assembled plasmonic logic gates that read DNA molecules as input and return plasmonic chiroptical signals as outputs are reported. Such logic gates are achieved on a DNA-based platform that logically regulate the conformation of a chiral plasmonic nanostructure, upon specific input DNA strands and internal computing units. With systematical designs, a complete set of Boolean logical gates are realized. Intriguingly, the logic gates could be endowed with adaptiveness, so they can autonomously alter their logics when the environment changes. As a demonstration, a logic gate that performs AND function at body temperature while OR function at cold storage temperature is constructed. In addition, the plasmonic chiroptical output has three distinctive states, which makes a three-state molecular logic gate readily achievable on this platform. Such DNA-based plasmonic logic gates are envisioned to execute more complex tasks giving these unique characteristics.     

Smart polymer grafted silica based drug delivery systems

Smart polymers are a special class of polymers, which respond to the various external stimuli by changing their properties. Recent developments in synthetic polymer chemistry have provided the possibility of designing and synthesis of various new stimuli-responsive polymers. These stimuli-responsive polymers can be used to prepare smart drug delivery systems (DDS) by grafting them on various nanomaterials. The main aim of this review is to present collective information on various stimuli-responsive polymers grafted on silica nanoparticles for the preparation of smart DDS. The stimuli covered are pH, temperature, redox, reactive oxygen species (ROS), glucose concentration, enzymes, magnetic field, and so forth. The structures of various stimuli-responsive polymers are shown with their relevance to the preparation of smart DDS. The crucial roles of macromolecular design and synthesis of smart polymers in the development of stimuli-responsive DDS are discussed with examples from literature and the challenges that still exist in this area of research are presented.     

Enzyme-responsive polymeric assemblies, nanoparticles and hydrogels

Being responsive and adaptive to external stimuli is an intrinsic feature characteristic of all living organisms and soft matter. Specifically, responsive polymers can exhibit reversible or irreversible changes in chemical structures and/or physical properties in response to a specific signal input such as pH, temperature, ionic strength, light irradiation, mechanical force, electric and magnetic fields, and analyte of interest (e.g., ions, bioactive molecules, etc.) or an integration of them. The past decade has evidenced tremendous growth in the fundamental research of responsive polymers, and accordingly, diverse applications in fields ranging from drug or gene nanocarriers, imaging, diagnostics, smart actuators, adaptive coatings, to self-healing materials have been explored and suggested. Among a variety of external stimuli that have been utilized for the design of novel responsive polymers, enzymes have recently emerged to be a promising triggering motif. Enzyme-catalyzed reactions are highly selective and efficient toward specific substrates under mild conditions. They are involved in all biological and metabolic processes, serving as the prime protagonists in the chemistry of living organisms at a molecular level. The integration of enzyme-catalyzed reactions with responsive polymers can further broaden the design flexibility and scope of applications by endowing the latter with enhanced triggering specificity and selectivity. In this tutorial review, we describe recent developments concerning enzyme-responsive polymeric assemblies, nanoparticles, and hydrogels by highlighting this research area with selected literature reports. Three different types of systems, namely, enzyme-triggered self-assembly and aggregation of synthetic polymers, enzyme-driven disintegration and structural reorganization of polymeric assemblies and nanoparticles, and enzyme-triggered sol-to-gel and gel-to-sol transitions, are described. Their promising applications in drug controlled release, biocatalysis, imaging, sensing, and diagnostics are also discussed.     

Energy transfer through heterogeneous dyes‐substituted fluorene‐containing alternating copolymers and their dual‐emission properties in the films

We report synthesis of the modified fluorene polymers tethered to the heterogeneous types of the fluorescent dyes at the cardo carbon for obtaining the dual‐emissive solid materials. A series of the alternating fluorene copolymers modified with pyrene or 9,10‐diphenylanthracene and BODIPY at the cardo carbon based on the red‐emissive donor–acceptor structure were prepared, and their characteristics were examined. From the measurements of the optical properties, the energy transfer efficiencies were evaluated. In summary, variable energy transfer efficiencies were observed between the side chains and from the side chain to the main chain. It was indicated that the energy transfer efficiencies were strongly depended on the types of the energy donor and the detection conditions as such in the solution or film. Furthermore, it was found that the cardo fluorene units can contribute to the suppression of the energy transfer in the condensed state. Finally, the dual‐emissive polymers were obtained in the film states. This is the first example, to the best of our knowledge, not only to offer systematic information on the energy transfer between the dye molecules and the polymer main‐chains via the cardo structure but also to demonstrate the polymer‐based optical materials with the dual‐emission properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2026–2035     

Cucurbituril Based Luminescent Materials in Aqueous Media and Solid State

Cucurbit[n]urils, the pumpkin shaped macrocyclic host molecules possessing a hydrophobic cavity and two identical carbonyl portals, have drawn a lot of attention in recent years due to their high-affinity yet dynamic molecular recognition properties in water. The reversible and stimuli-responsive nature of their host-guest complexes imparts “smart” features leading to materials with intriguing optical, mechanical and morphological properties. In this review, we focus on the design of cucurbituril based luminescent materials in aqueous media as well in solid or film state. The design principles of fluorescent complexes, small assemblies as well as supramolecular polymers along with their stimuli-responsive properties and applications in diverse areas such as optoelectronic devices, light harvesting, anti-counterfeiting and information technology, cell imaging, etc are highlighted with selected examples from recent literature. We also discuss examples of room temperature phosphorescent materials derived from purely organic luminogens in the presence of cucurbiturils.     

新型基于3,6-咔唑与噻吩衍生物的红光聚合物的合成与性能研究

用Suzuki偶合反应制备了一系列N-(2-乙基己基)-3,6-咔唑(Cz)与4,7-二(4-己基噻吩)-2,1,3-苯并噻二唑(DHTBT)的共聚物, 研究该类聚合物的电化学、光学和电致发光性能. 在薄膜状态下, 即使DHTBT含量为1%的聚合物也发生了从Cz链段到DHTBT单元的有效的能量转移. 光致发光光谱随着DHTBT含量的增加, 从645 nm红移至690 nm. PCzDHTBT1获得了71%的薄膜光致发光效率. 以该类聚合物为发光层的器件的EL光谱也随着DHTBT含量的增加从635 nm红移至680 nm. 由PCzDHTBT15制作的结构为ITO/PEDOT:PSS/polymer/Ba/Al的器件得到了0.61%的外量子效率.     

The magic of integration:Exploring the construction of dithienylethene-based infinite coordination polymers and their synergistic effect for gaseous ammonia probe applications

Infinite coordination polymers are recognized as excellent platform for functionalization.Dithienylethene motifs,which are one of the most attractive functional moieties,were incorporated into an infinite coordination polymer,to deliver a‘‘smart’’porous material that can response to external stimuli.The obtained dithienylethene-based infinite coordination polymers(named Cu-DTEDBA)share the advantages of both infinite coordination polymers(porosity and stability)and dithienylethene motifs(photochromism).The physical and chemical properties of Cu-DTEDBA were characterized by FTIR,TEM,SEM,XRD,TGA,UV–vis,EDX and BET.Moreover,the combination of dithienylethene and infinite coordination polymers gives rise to a synergistic effect,which induces functional behaviors of ammonia sensor applications.Both open and closed forms of Cu-DTEDBA exhibit distinct colorimetric change upon exposure to gaseous ammonia,which is not observed in dithienylethene free molecules.     

Recent progress on switchable rotaxanes

Switchable rotaxanes are currently attracting considerable attention from chemists, physicists and materials scientists because of their potential to perform relative inter-component positional changes in response to external stimuli and the potential applications in the fields such as molecular machines, molecular switches, molecular logic gates and memory devices. This tutorial review summarizes recent work on switchable rotaxanes and their potential applications.     

DNA‐Based Adaptive Plasmonic Logic Gates

Self‐assembled plasmonic logic gates that read DNA molecules as input and return plasmonic chiroptical signals as outputs are reported. Such logic gates are achieved on a DNA‐based platform that logically regulate the conformation of a chiral plasmonic nanostructure, upon specific input DNA strands and internal computing units. With systematical designs, a complete set of Boolean logical gates are realized. Intriguingly, the logic gates could be endowed with adaptiveness, so they can autonomously alter their logics when the environment changes. As a demonstration, a logic gate that performs AND function at body temperature while OR function at cold storage temperature is constructed. In addition, the plasmonic chiroptical output has three distinctive states, which makes a three‐state molecular logic gate readily achievable on this platform. Such DNA‐based plasmonic logic gates are envisioned to execute more complex tasks giving these unique characteristics.