Anthryl-doped conjugated polyelectrolytes as aggregation-based sensors for nonquenching multicationic analytes

The fluorescence-based detection of nonquenching, multicationic small molecules has been demonstrated using a blue-emitting, polyanionic poly(p-phenylene ethynylene) (PPE) doped with green-emitting exciton traps (anthryl units). Multicationic amines (spermine, spermidine, and neomycin) were found to effectively induce the formation of tightly associated aggregates between the polymer chains in solution. This analyte-induced aggregation, which was accompanied by enhanced exciton migration in the PPE, ultimately led to a visually noticeable blue-to-green fluorescence color change in the solution. The aggregation-based sensor exhibited poor sensitivity toward dicationic and monocationic amines, demonstrating that a conjugated polyelectrolyte sensor relying on nonspecific, electrostatic interactions may still attain a certain level of selectivity.     

Simple Conjugated Polymers with On‐Chain Phosphorescent Iridium(III) Complexes: Toward Ratiometric Chemodosimeters for Detecting Trace Amounts of Mercury(II)

For the development of excellent optical probes for mercury(II), a series of simple conjugated polymers that contain phosphorescent iridium(III) complexes as receptors for mercury(II) were designed and synthesized. These conjugated polymers showed energy transfer from the polymer host to iridium(III) complex guest in both solution and the solid state. Unexpectedly, they can work as excellent polymer chemodosimeters for mercury(II) by utilizing the mercury(II)‐induced decomposition of iridium(III) complex. They exhibit a pronounced optical signal change with switchable phosphorescence and fluorescence, even when the concentration of a solution of mercury(II) in THF was as low as 0.5 ppb. With the addition of mercury(II), the phosphorescent emission intensity of iridium(III) complexes was quenched completely. As the emission from polymer backbones increased, the emission wavelength was redshifted simultaneously, thereby realizing ratiometric detection. Excellent selectivity toward mercury(II) over other potentially interfering cations was also realized. In addition, an obvious emission color change of polymer solution from red to yellow‐green was observed, thus realizing a “naked‐eye” detection of mercury(II). More importantly, the solid films of these polymer chemodosimeters also exhibited high sensitivity and rapid response to mercury(II), thereby demonstrating the possibility of the fabrication of sensing devices with fast and convenient detection of mercury(II). The sensing mechanism was also investigated in detail. This is the first report on chemodosimeters based on conjugated polymers with phosphorescent iridium(III) complexes.     

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.     

Highly emissive conjugated polymer excimers

Conjugated polymers often display a decrease of fluorescence efficiency upon aggregation due in large part to enhanced interpolymer interactions that produce weakly emissive species generally described as having excimer-like character. We have found that poly(phenylene ethynylene)s with fused pendant [2.2.2] ring structures having alkene bridges substituted with two ester groups function to give highly emissive, broad, and red-shifted emission spectra in the solid state. To best understand the origin of this new solid-state emissive species, we have performed photophysical studies of a series of different materials in solution, spin-coated thin films, solid solutions, and Langmuir films. We conclude that the new, red-shifted, emissive species originate from excimers produced by interchain interactions being mediated by the particular [2.2.2] ring system employed. The ability to design structures that can reliably produce highly emissive conjugated polymer excimers offers new opportunities in the emission tailoring of electroluminescence and sensory devices.     

A novel conjugated polymer containing alternating p‐ and n‐type moieties with balanced properties of conducting holes and electrons

A new electroluminescent conjugated polymer consisting of 2,2′‐bipyridylenevinylene (BPyV) and 2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene (MEH‐PV) moieties (BPy‐MEH‐PPV), was synthesized by incorporating an n‐dope type moiety, BPyV, and a p‐dope type moiety, MEH‐PV, into the polymer chain. This facile method provides a new approach to the synthesis of conjugated polymers with balanced ability of conducting electrons and holes. PBy‐MEH‐PPV exhibits tunable optical properties through protonation, and the emissive color can be progressively changed from orange to deep red depending on the degree of protonation.     

Modulating Photo‐ and Electroluminescence in a Stimuli‐Responsive π‐Conjugated Donor–Acceptor Molecular System

Functional organic materials that display reversible changes in fluorescence in response to external stimuli are of immense interest owing to their potential applications in sensors, probes, and security links. While earlier studies mainly focused on changes in photoluminescence (PL) color in response to external stimuli, stimuli‐responsive electroluminescence (EL) has not yet been explored for color‐tunable emitters in organic light‐emitting diodes (OLEDs). Here a stimuli‐responsive fluorophoric molecular system is reported that is capable of switching its emission color between green and orange in the solid state upon grinding, heating, and exposure to chemical vapor. A mechanistic study combining X‐ray diffraction analysis and quantum chemical calculations reveals that the tunable green/orange emissions originate from the fluorophore's alternating excited‐state conformers formed in the crystalline and amorphous phases. By taking advantage of this stimuli‐responsive fluorescence behavior, two‐color emissive OLEDs were produced using the same fluorophore in different solid phases.     

Rotaxanated conjugated sensory polymers

Two highly emissive conjugated polymers with tethered rotaxane repeat units are reported. Hydrogen bonding between acidic alcohols and the N-heteroaromatic groups in the rotaxanes attenuates polymer fluorescence. In addition, the rotaxane groups create precise three-dimensional pockets for metal binding, which results in fluorescence quenching. Exposing thin films of Zn-doped polymers to alcohol vapors reverses the quenching by up to 25%.     

Newly synthesized polybenzoxazole derivative with an adjacent hydroxyphenyl ring for optical sensing

A photoluminescent polymer with a 2‐(2′‐hydroxyphenyl)benzoxazole unit in the molecular main chain was synthesized through the deprotection reaction of a precursor polymer. The amorphous, conjugated polymer emitted green light, both in solution and as a solid, with a fluorescence emission maximum at 518 nm from an excited keto tautomer because of excited‐state intramolecular proton transfer. The polymer showed different fluorescence emission spectra in solvents with different polarities because of intramolecular hydrogen‐bond interruption. The intramolecular hydrogen‐bond‐induced emission change was successfully used as a sensitive sensing signal for metal cations as expected, the polymer acting as a fluorescence‐based chemosensor. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1397–1403, 2005     

Electrochromic material containing unsymmetrical substituted N,N,N′,N′‐tetraaryl‐1,4‐phenylenediamine: Synthesis and their optical,electrochemical, and electrochromic properties

A novel dibromo compound containing unsymmetrical substituted bi‐triarylamine was synthesized. A conjugated polymer was prepared via the Suzuki coupling from the newly prepared dibromo compound and 9,9‐dioctylfluorene‐2,7‐bis(trimethyleneboronate). The glass transition temperature (T_g) of the conjugated polymer was 140 °C, 10% weight‐loss temperatures (T_d10) in nitrogen was 458 °C, and char yield at 800 °C in nitrogen higher than 64%. Cyclic voltammogram of the polymer film cast onto an indium‐tin oxide (ITO)‐coated glass substrate exhibited two reversible oxidation redox couples at 0.70 and 1.10 V versus Ag/Ag⁺ in acetonitrile solution. The polymer films revealed excellent stability of electrochromic characteristics, with a color change from yellow green of the neutral form to the dark green and blue of oxidized forms at applied potentials ranging from 0 to 1.3 V. The color switching time and bleaching time were 4.25 and 7.22 s for 860 nm and 5.51 s and 6.48 s for 560 nm. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1469–1476, 2010     

Synthesis and characterization of a new green‐emitting poly(phenylenevinylene) derivative containing alkylsilylphenyl pendant

A new type of processable green‐emissive polymer containing alkylsilylphenyl units was synthesized via Gilch polymerization. The resulting polymer was soluble in organic solvents and was spin‐cast to make a thin film. A light‐emitting diode was fabricated by the polymer being sandwiched between indium tin oxide and metal electrodes. A strong green emission at 524 nm was observed from the various device configurations made by the newly synthesized polymer. The polymer had a strong absorption band around 427 nm that was attributable to a π–π* transition of the conjugated segments of the polymer. A current–voltage–luminance curve showed typical rectifying diode characteristics. The polymer had a very high molecular weight (number‐average molecular weight = ∼300,000) with a polydispersity of about 3 and good thermal stability up to 400 °C. The brightness at 13 and 17 V was about 1000 and 5900 cd/m², respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4185–4193, 2000     

Engineering Stacks of V‐Shaped Polyaromatic Compounds with Alkyl Chains for Enhanced Emission in the Solid State

A V‐shaped bisanthracene derivative with three butyl groups formed two types of emissive solids that display bluish green and blue fluorescence (Φ_F=72 and 32 %, respectively), depending on the preparation conditions. The crystal and powder X‐ray analyses reveal that the highly emissive solid adopts a head‐to‐head arrangement with discrete stacks of the anthracene moieties, whereas the moderately emissive solid adopts a head‐to‐tail arrangement without the stacks. The obtained molecular arrangements are transformed by thermal stimuli accompanying the change in fluorescence. Furthermore, large enhancements of dye emissions (12–45‐fold) through highly efficient host–guest energy transfer were achieved in the solid state by adding minute amounts of various fluorescent dyes (e.g. rubrene and Nile red) to the V‐shaped compound.     

Carbon dioxide-controlled assembly based on conjugated polymer and boron nitride

C02-controlled assembly of conjugated polymer and boron nitride(BN)was fabricated via electrostatic and hydrophobic interactions between the BN fiber and conjugated polymer of PFBT containing fluorene units and 2,1,3-benzothiadiazole units.C02,an effective and green stimulus for regulating the assembly of PFBT and BN fibers,leads to an obvious fluorescence variation.Moreover,PFBT enables the assembly with the signal amplification and light-harvesting properties.This work provides a new triggering method to construct intelligent conjugated polymer-based platform,and offers fluorescence monitoring strategy for carbon dioxide capture.     

Self‐Assembly of π‐Conjugated Gelators into Emissive Chiral Nanotubes: Emission Enhancement and Chiral Detection

A series of new π‐conjugated gelators that contain various aromatic rings (phenyl, naphthyl, 9‐anthryl) and amphiphilic L ‐glutamide was designed, and their gel formation in organic solvents and self‐assembled nanostructures was investigated. The gelators showed good gelation ability in various organic solvents that ranged from polar to nonpolar. Those gelator molecules with small rings such as phenyl and naphthyl self‐assembled into nanotube structures in most organic solvents and showed strong blue emission. However, the 9‐anthryl derivative formed only a nanofiber structure in any organic solvent, probably owing to the larger steric hindrance. All of these gels showed enhanced fluorescence in organogels. Furthermore, during the gel formation, the chirality at the L ‐glutamide moiety was transferred to the nanostructures, thus leading to the formation of chiral nanotubes. One of the nanotubes showed chiral recognition toward the chiral amines.     

Anisotropic optical properties in electroluminescent conjugated polymers based on grazing angle photoluminescence measurements

Grazing angle photoluminescence (GPL) originates from a waveguided light emitted at grazing angle to the substrate due to the total internal reflections, and the light emission is polarized with enhanced intensity at selective mode wavelength. GPL measurements reveal the optical anisotropy of luminescent conjugated polymers, in particular, the alignment of emitting dipoles from which emission occurs, in contrast to spectroscopic ellipsometry measurements that give the anisotropy in the absorption. Based on the GPL emission intensities and spectra, we investigate the anisotropic optical properties in electroluminescent poly(9,9'-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) conjugated polymer thin films of different molecular weights (M(n) = 9-255 kg/mol), both in the pristine and annealed states. The optical anisotropy in F8BT films generally increases with molecular weight, suggesting that higher molecular weight polymers with longer chains are more likely to lie in-plane to the substrate. Upon annealing, high molecular weight F8BT films show even a higher degree of anisotropy, in contrast to low molecular weight F8BT films that become more isotropic. Annealing causes the polymer chains to rearrange and adopt a configuration in which the interchain exciton migration to better ordered low energy (LE) emissive states is strongly suppressed. We observe that the emissive states in F8BT are strongly affected by the local polymer chain arrangement, producing the less ordered high energy (HE) emissive states near the substrate interface where there is a higher degree of chain disorder and the LE states in the bulk of the film. When spin coated onto a quartz substrate precoated with a poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) layer, films of F8BT show severe luminescence quenching near the PEDOT:PSS interface for both the LE and HE emissive states, but a selective quenching of the LE states in the bulk of the film. These observations have important implications for fabricating efficient electronic devices using conjugated polymers as an active material, since the performance of these devices will strongly depend on anisotropic optical properties of electroluminescent conjugated polymers.     

2-Aza-1,3-butadiene derivatives featuring an anthracene or pyrene unit: highly selective colorimetric and fluorescent signaling of Cu2+ cation

[Structure: see text] A new probe based on an anthryl derivative bearing an azadiene side chain selectively senses Cu2+ in acetonitrile through two different channels: the yellow-to-orange color change and a remarkable enhancement of the fluorescence, whereas the pyrenyl analogous behaves as a fluorescent sensor for Cu2+ and Hg2+ in aqueous environment.     

Single Benzene Green Fluorophore: Solid‐State Emissive,Water‐Soluble,and Solvent‐ and pH‐Independent Fluorescence with Large Stokes Shifts

Benzene is the simplest aromatic hydrocarbon with a six‐membered ring. It is one of the most basic structural units for the construction of π conjugated systems, which are widely used as fluorescent dyes and other luminescent materials for imaging applications and displays because of their enhanced spectroscopic signal. Presented herein is 2,5‐bis(methylsulfonyl)‐1,4‐diaminobenzene as a novel architecture for green fluorophores, established based on an effective push–pull system supported by intramolecular hydrogen bonding. This compound demonstrates high fluorescence emission and photostability and is solid‐state emissive, water‐soluble, and solvent‐ and pH‐independent with quantum yields of Φ=0.67 and Stokes shift of 140 nm (in water). This architecture is a significant departure from conventional extended π‐conjugated systems based on a flat and rigid molecular design and provides a minimum requirement for green fluorophores comprising a single benzene ring.     

Single Benzene Green Fluorophore: Solid‐State Emissive,Water‐Soluble,and Solvent‐ and pH‐Independent Fluorescence with Large Stokes Shifts

Benzene is the simplest aromatic hydrocarbon with a six‐membered ring. It is one of the most basic structural units for the construction of π conjugated systems, which are widely used as fluorescent dyes and other luminescent materials for imaging applications and displays because of their enhanced spectroscopic signal. Presented herein is 2,5‐bis(methylsulfonyl)‐1,4‐diaminobenzene as a novel architecture for green fluorophores, established based on an effective push–pull system supported by intramolecular hydrogen bonding. This compound demonstrates high fluorescence emission and photostability and is solid‐state emissive, water‐soluble, and solvent‐ and pH‐independent with quantum yields of Φ=0.67 and Stokes shift of 140 nm (in water). This architecture is a significant departure from conventional extended π‐conjugated systems based on a flat and rigid molecular design and provides a minimum requirement for green fluorophores comprising a single benzene ring.     

Characterization of tectoRNA assembly with cationic conjugated polymers

Association between RNAs with preprogrammed molecular recognition units can be quantified by using cationic, water-soluble conjugated polymers. The method uses a fluorophore-labeled probe RNA (RNA-F*), which is treated with a target structure (RNA-T). Heterodimer formation, (RNA-T/RNA-F*), increases the total negative charge on the F*-bearing macromolecule and reduces the number of negatively charged molecules (relative to unbound RNA-T+ RNA-F*). On the basis of electrostatic interactions, we anticipated more effective binding between CCP and (RNAT/RNA-F*), a reduction of the average CCP- - -F* distance, and more effective FRET upon excitation of the conjugated polymer. The resulting signals benefit from the optical amplification characteristic of emissive conjugated polymers. Solution dissociation constants can be determined by monitoring F* intensity changes as a function of [RNA-F*] and the ratio: [I(T) - I(NB)]/I(NB), where I(T) and I(NB) are the F* intensities in the presence of the target RNA (RNA-T) and a nonbinding RNA (RNA-NB), respectively, while keeping the concentration of the conjugated polymer constant. By focusing on [I(T) - I(NB)]/I(NB) as a function of RNA concentration, one can detect the concentration range wherein increased fluorescence is the result of dimerization.     

Synthesis and photophysical properties of polyfluorenes bearing silicon‐based functional groups

Five polyfluorenes bearing bulky trimethylsilyl (PTMS1 and PTMS2), tris(trimethylsilyl)silyl (PTTMS1), and silsesquioxane groups (PPOSS1 and PPOSS2) were synthesized through palladium‐catalyzed Suzuki coupling reactions. In the solution state, every polymer showed comparable ultraviolet–visible spectra, and they emitted blue light with high quantum efficiency. In the solid state, however, three trimethylsilyl‐functionalized polyfluorenes indicated redshifts of the fluorescence peak. In particular, PTMS1 and PTTMS1, having a hydrogen at the C‐9 position of fluorene, also showed green‐light emissions. After the annealing of the spin‐coated films, the blue‐emissive peak decreased and the green‐emissive peak became stronger in the photoluminescence spectra of three trimethylsilyl‐functionalized polyfluorenes. In contrast, PPOSS2 showed a pure blue‐light emission in the film state and even after the thermal treatment, which could be accomplished by the encapsulation of the polymer chains by the large polyhedral oligomeric silsesquioxane molecule. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2119–2127, 2005     

含三苯胺单元的超支化共轭聚合物的合成、表征及应用

本实验采用Wittig方法制得了未封端和封端的超支化聚三苯胺-对苯乙烯撑型聚合物,对两种共轭聚合物进行了表征和性能测试.聚合物溶液和固体膜在紫外光照射下均发出较强的绿光.首次对这类聚合物在硝基芳烃化合物荧光猝灭能力进行了初步研究,结果表明:与未封端产物相比,封端后的超支化共轭聚合物在邻硝基甲苯(o-NT)的荧光猝灭效率上有明显提高,当o-NT浓度为21.5×10^-3mol/L时,荧光猝灭效率达到97%.这类共轭聚合物不仅合成操作较为简便,猝灭效率也较高,是一种很有潜力的硝基芳烃化合物荧光检测材料.