Thiophene-Based Covalent Organic Frameworks: Synthesis,Photophysics and Light-Driven Applications

Porous crystalline materials, such as covalent organic frameworks (COFs), have emerged as some of the most important materials over the last two decades due to their excellent physicochemical properties such as their large surface area and permanent, accessible porosity. On the other hand, thiophene derivatives are common versatile scaffolds in organic chemistry. Their outstanding electrical properties have boosted their use in different light-driven applications (photocatalysis, organic thin film transistors, photoelectrodes, organic photovoltaics, etc.), attracting much attention in the research community. Despite the great potential of both systems, porous COF materials based on thiophene monomers are scarce due to the inappropriate angle provided by the latter, which hinders its use as the building block of the former. To circumvent this drawback, researchers have engineered a number of thiophene derivatives that can form part of the COFs structure, while keeping their intrinsic properties. Hence, in the present minireview, we will disclose some of the most relevant thiophene-based COFs, highlighting their basic components (building units), spectroscopic properties and potential light-driven applications.     

基于荧光共轭聚电解质的生物分子检测*

共轭聚电解质综合了传统共轭聚合物的光电性质和聚电解质的水溶性特点,使其在新一代化学生物荧光传感器中获得多种应用。本文总结了近五年来报道的共轭聚电解质（聚芴、聚噻吩、聚苯撑乙烯、聚苯撑乙炔等）用于检测生物分子的研究进展,并对共轭聚电解质的应用前景进行了展望。     

Design and Synthesis of Conjugated Starburst Molecules for Optoelectronic Applications

In recent years, conjugated starburst molecules, which possess a core unit with radial arms linked to the central axle, have become the research topic owing to their well‐defined chemical structures, good solution processability, excellent reproducibility, and superior optoelectronic properties. The increasing interest in starburst systems is evidenced by progressively more frequent investigation on the use of these materials in optoelectronics. The ability to modify chemical structures through control over the core and arms on a molecular level can directly affect the electronic and electroluminescent characteristics of the resulting materials. In this review, we summarize and discuss main progress in our group concerning the rapidly developing field, in which strategies for the design and construction of starbursts are presented at length. Moreover, their application in organic light‐emitting diodes (OLEDs) and organic semiconductor lasers (OSLs) are demonstrated as well, exploring the influence of molecular structures on the optoelectronic properties. Challenges and outlooks are also given at last.     

水溶性共轭聚电解质

水溶性共轭聚电解质主要是指含离子型官能团侧链的共轭聚合物,可在水或其它极性有机溶剂中能够溶解。这类化合物把传统共轭聚合物的光电性质和聚电解质的水溶性特点结合在一起,显示出的一些独特性质,可在新一代光电器件制作和化学生物荧光传感器中获得多样的应用。本文总结了近10年来报道的水溶性共轭聚电解质的结构特点和合成方法,以及对不同化学或物理条件下光物理性质的研究,归纳了它们在新一代光电器件制作和荧光传感中的应用,并在此基础上提出了水溶性共轭聚电解质研究中尚待解决的问题,并展望了水溶性共轭聚电解质的应用前景。     

Conjugated Polyelectrolytes as New Platforms for Drug Screening

In recent years, conjugated polyelectrolytes (CPEs) have attracted increasing attention for their applications in highly sensitive biosensors by taking advantage of their unique optical amplification properties. In comparison to previous applications tailored for highly sensitive biomacromolecule detection, this Focus Review highlights recent research efforts in the development of water‐soluble CPEs as a new class of optical platforms for the screening of potential drugs. Three types of biological targets for the search of small‐molecule active drugs are described: nucleic acids, enzymes, and RNA–protein complexes. Future research directions for drug screening based on CPEs are also presented.     

An Optical Approach for Drug Screening Based on Light‐Harvesting Conjugated Polyelectrolytes

Drugs turn the light off : Conjugated polyelectrolytes (CPEs) have been used in fluorescent assays for real‐time screening of small molecules that prevent the RNA–protein complexation that is important for virus replication and thereby can be considered potential initial candidates for drug discovery (see picture).

     

Covalently Scaffolded Inter‐π‐System Orientations in π‐Conjugated Polymers and Small Molecule Models

Organic π‐conjugated polymers have emerged as one of the most fascinating classes of materials as they have found utility in a host of plastic electronics technologies. The distance between π‐systems and their relative orientation dictate energy/charge transfer, conductivity, and photophysical properties of these materials in bulk. This Feature Article discusses π‐conjugated polymers and model compounds in which specific inter‐π‐system interactions are covalently enforced and the effect that the scaffolding has on optoelectronic properties.

     

Cationic and Anionic Conjugated Polyelectrolytes: Aggregation‐Mediated Fluorescence Energy Transfer to Dye‐Labeled DNA

An electrostatic complex of water‐soluble conjugated polyelectrolytes (CPs) between anionic poly(9,9‐bis(4′‐sulfonatobutyl)fluorene‐co‐alt‐1,4‐phenylene) disodium salt (a‐PFP) and cationic poly(9,9‐bis((6′‐N,N,N,‐trimethylammonium)hexyl)fluorene‐co‐2,1,3‐bezothiadiazole) dibromide (85:15) (c‐PFB₁₅) was tested as a fluorescence resonance energy transfer (FRET) donor to Texas Red (TR)‐labeled single‐stranded DNA (ssDNA‐TR) via two‐step FRET processes. Electrostatic complexation of a‐PFP and c‐PFB₁₅ in water leads to aggregation of polymer chains, a concomitant reduction of intersegment distances, and energy transfer to the benzothiadiazole (BT) segments. The following complexation with ssDNA‐TR leads to energy transfer from BT to TR via two‐step FRET processes. This detection schematic shows an FRET‐induced signal amplification, which can be achieved by adjusting the charge ratio in the cationic/anionic CP complex and controlling the number density of the binding CPs around the acceptor, resulting in enhanced antenna effects and sensitivity in CP‐based FRET DNA detection assays.

     

Fluorescence Turn‐On Detection of Nitric Oxide in Aqueous Solution Using Cationic Conjugated Polyelectrolytes

A fluorescent turn‐on detection for nitric oxide in aqueous solution is developed using cationic conjugated polymers. The assay benefits from the sensitivity of optical signals from conjugated polymers and the simplicity of fluorescence measurement techniques. The assay contains three elements: a cationic conjugated polymer that contains imidazole moieties, Cu²⁺ ions, and the target nitric oxide. The highly fluorescent conjugated polymer coordinates to Cu²⁺ ions through weak N · · · Cu interactions, and its fluorescence is efficiently quenched by a photo‐induced electron transfer process (‘off’ state). In the presence of nitric oxide, the transformation of the paramagnetic Cu²⁺ ion into a diamagnetic Cu¹⁺ ion inhibits the quenching and, therefore, the fluorescence of the conjugate polymer is recovered (‘on’ state). Other biologically relevant reactive nitrogen species, such as NOBF₄, NaNO₂, and NaNO₃ don't exhibit the fluorescence recovery of the conjugated polymer under the same conditions as nitric oxide. The cationic conjugated polymer/Cu²⁺ complex can thus be used as a platform to detect nitric oxide in aqueous solution with high sensitivity and selectivity.

     

Doping the Backbone of π‐Conjugated Polymers with Tricoordinate Boron: Synthetic Strategies and Emerging Applications

The doping of π‐conjugated organic compounds with trivalent boron atoms produces materials with intriguing properties and functions that result from the interaction of the π‐electron system with the vacant p orbital on boron. This offers unique opportunities in various applications such as organic (opto)electronics, biomedical imaging, and sensors for physiologically relevant anions or amines, as demonstrated by numerous examples on the molecular scale. Recently, the B‐doping strategy has been expanded to polymer chemistry with a view to benefit from the best of both worlds. Herein, recent advances in the synthesis of π‐conjugated polymers doped with tricoordinate boron in the backbone are reviewed. Selected applications are described where these functional materials have already been successfully implemented.     

Microparticle‐Supported Conjugated Polyelectrolyte Brushes Prepared by Surface‐Initiated Kumada Catalyst Transfer Polycondensation for Sensor Applications

A ‘grafting‐from’ approach to synthesize microparticle‐supported conjugated polyelectrolyte brushes is presented. Poly(3‐bromohexylthiophene) is selectively grown from monodisperse organosilica microparticles by surface‐initiated Kumada catalyst‐transfer polycondensation (SI‐KCTP) and then ionizable amino groups are introduced by a two‐step polymer analogous transformation. Optical properties of the resulting microparticle‐supported conjugated polyelectrolyte brushes were found to be dependent on the surrounding chemical environment and thus the particles are promising materials for sensor applications.

     

Highly Selective Fluorescence Detection for Mercury (II) Ions in Aqueous Solution Using Water Soluble Conjugated Polyelectrolytes

A highly selective assay method has been developed to detect mercury (II) (Hg²⁺) ions using cationic conjugated polymer (CCP). The transduction mechanism is based on a Hg²⁺ promoted reaction. In the absence of Hg²⁺ ions, the CCP can form the complex with an anionic 1,3‐dithiole‐2‐thione derivative through electrostatic interactions. The fluorescence of CCP is efficiently quenched by 1,3‐dithiole‐2‐thione derivative via an electron transfer process. Upon adding Hg²⁺ ions, the transformation of 1,3‐dithiole‐2‐thione into 1,3‐dithiole‐2‐one inhibits the quenching, and the fluorescence of CCP is recovered. Distinguishing aspects of this assay include the signal amplification of CCPs and a specific Hg²⁺ promoted reaction. By triggering the change in the emission intensity of CCP, it is possible to detect Hg²⁺ ions in aqueous solution.

     

Synthesis, Photophysics and Morphology of a Conjugated Polymer with Azobenzene Building Block in the Backbone

A conjugate polymer poly[p‐(phenyleneethylene)‐alt‐(phenyleneazophenyleneethylene)] (PPEPAPE) containing azobenzene building block in the polymer backbone was synthesized via Sonogashira cross‐coupling of 4,4′‐diiodoazobenzene and 1,4‐diethynyl‐2,5‐didodecyloxybenzene. All the monomers and the resulting polymer were well characterized. The polymer had a relatively high molecular weight and showed very good solubility (≧10 mg/mL) in common organic solvents. The photophysics of this polymer in solution and in film was investigated. The surface morphology of the films was studied by scanning electron microscope (SEM) and the relationship between the morphology and absorbance was discussed. This polymer has good film‐forming property, broad absorbance and no emission, which might make it a good candidate for the photovoltaic material in the solar cell.     

Glucosamine Hydrochloride Functionalized Water‐Soluble Conjugated Polyfluorene: Synthesis,Characterization, and Interactions with DNA

Novel glucosamine hydrochloride functionalized water‐soluble conjugated polyfluorene was easily synthesized through Cu(I)‐catalyzed azide/alkyne “click” ligation and Suzuki coupling polymerization. The water‐solubility and biocompatibility of the polymer were improved after grafting glucosamine hydrochloride to the side chains of the conjugated polymer. As a fluorescent model system of chitosan, its interaction with single‐stranded DNA was studied by spectrofluorometric titration.

     

Photophysics and morphology of a polyfluorene donor–acceptor triblock copolymer for solar cells

We present a study of the optical, structural and device properties of a polyfluorene (PFM)‐based (PFM‐F8BT‐PFM) donor–acceptor triblock copolymer for use in an organic solar cell. Neutron reflectivity is employed to probe the vertical composition profile before and after thermal annealing while the crystallinity was examined using grazing incidence wide‐angle X‐ray. The absorption spectra and photoluminescence emission for the triblock and analogous blend of PFM with F8BT reveal a greater degree of intermixing in the triblock. However, the triblock copolymer exhibits exciplex emission, which necessitates a geminate polar pair; long‐lived exciplex states are detrimental in organic photovoltaic devices. The triplet yield in the triblock and the blend is estimated using photoinduced absorption, with the triblock copolymer generating a triplet population 20 times that of the blend. This is far from ideal as triplets are wasted states in organic photovoltaic devices and they can also act as scavengers of polarons reducing the efficiency even more. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1705–1718     

Functionalized Conjugated Polyelectrolytes for Biological Sensing and Imaging

Conjugated polyelectrolytes (CPEs) are macromolecules with highly delocalized π‐conjugated backbones and charged side chains, which are unique types of active materials, with wide applications in optoelectronics, sensing, imaging, and therapy. By attaching specific groups (e.g., recognition elements, magnetic resonance (MR) contrast agents, gene carriers, and drugs) to the side chain or backbone of CPEs, functionalized CPEs have been developed and used for specific biological applications. In this account, we summarize the recent progress of functionalized CPEs with respect to their synthesis and biomedical applications. Future perspectives are also discussed at the end.