A fluorene-containing water-soluble poly(p-phenyleneethynylene) derivative: Highly fluorescent and sensitive conjugated polymer with minor aggregation in aqueous solution

A novel cationic fluorene-containing water-soluble poly(p-phenyleneethynylene) (PPE) derivative, poly[(9,9-bis{6′-[(N,N-diethyl)-N-methylammonium]hexyl}-2,7-fluorenyleneethynylene)-alt-co-(2,5-bis{3′-[(N,N-diethyl)-N-methylammonium]-1′-oxapropyl}-1,4-phenylene)] tetraiodide (P1′), was synthesized through Sonogashira reaction and a post-polymerization treatment. P1′ emits bright blue fluorescence in H₂O with a high photoluminescence quantum yield (Φ_pl=26%). Studies on the optical properties and quenching experiments with in H₂O and MeOH show that P1′ presents minor aggregation and high Stern-Volmer constant (K_sv=2.4×10⁸ M⁻¹) in aqueous solution. The remarkably reduced tendency towards aggregation, relative to previously reported water-soluble PPEs, made the optical properties of P1′ almost insensitive to the disturbance from the common ions (non-quencher) in the solution.     

A highly selective and sensitive fluorescence chemosensor based on optically active polybinaphthyls for Hg

The chiral polymer was synthesized by the polymerization of 4,7-diethynylbenzo[2,1,3]-thiadiazole (M-1) with (R)-6,6′-dibutyl-3,3′-diiodo-2,2′-bis(diethylaminoethoxy)-1,1′-binaphthyl (R-M-1) via Pd-catalyzed Sonogashira reaction. The chiral polymer has orange fluorescence due to the extended π-electronic structure between binaphthyl unit and benzo[2,1,3]thiadiazole (BT) group via ethynyl bridge. The responsive optical properties of the polymer on various metal ions were investigated by fluorescence spectra. The fluorescence of the chiral polymer can produce the pronounced enhancement as high as 1.8-fold upon addition of 1:2 molar ratio of Hg²⁺. Compared with other cations, such as K⁺, Mg²⁺, Pb²⁺, Co²⁺, Ni²⁺, Ag⁺, Cd²⁺, Cu²⁺, Zn²⁺, Mn²⁺ and Fe³⁺, Hg²⁺ can produce the pronounced fluorescence response of the polymer. The result indicates this kind of chiral polybinaphthyls incorporating diethylamino and benzo[2,1,3]thiadiazole (BT) moieties as receptors exhibits highly sensitive and selective behavior for Hg²⁺ detection.     

A highly selective ratiometric fluorescent sensor for Hg2+ based on 1,8‐naphthalimide

A sulfur probe based on 1,8‐naphthalimide was designed and synthesised, and its sensing behaviour towards a mercury ion was investigated by fluorescence spectroscopy. The probe showed higher selective recognition towards Hg²⁺ than towards other metal ions in methanol solution. Compared with 4‐amino‐substituted naphthalimide derivatives, the probe exhibited different fluorescent characteristics for sensing Hg²⁺. The novel, reaction‐based probe is recommended for selective recognition of Hg²⁺ with significant fluorescence change.     

A bipyridine-containing water-soluble conjugated polymer: Highly efficient fluorescence chemosensor for convenient transition metal ion detection in aqueous solution

A novel sulfonato-functionalized water-soluble conjugated polymer (WSCP), which containing 2′2-bipyridine units as receptors for transition metal ions in the main chain was successfully synthesized by Sonogashira-coupling reaction for the first time. This polymer could easily dissolve in water (5 mg/mL) and some polar organic solvents such as methanol. Its fluorescence in aqueous solution can be completely quenched upon addition of transition metal ions. The K_sv of different transition metal ions in aqueous solution were much higher than previous reports in organic solutions and showed highest selectivity to Ni²⁺. These results opened opportunities for developing novel chemosensors by introducing selective fluorescent chromophore into the water-soluble conjugated backbone.     

Synthesis, characterization and self-assembly behavior in water as fluorescent sensors of cationic water-soluble conjugated polyfluorene-b-poly(N-isopropylacrylamide) diblock copolymers

A series of well-defined novel water-soluble diblock copolymers containing conjugated amino-terminal polyfluorene (PF) block and coil-like poly(N-isopropylacrylamide) (PNIPAM) have been successfully synthesized through atom transfer radical polymerization (ATRP) initiated by a 2-bromoisobutyrate end-capped PF macroinitiator using CuCl/HMTETA (1,1,4,7,10,10-hexamethyltriethylenetetramine) as the catalyst. The first-order kinetic plots indicate the presence of a constant number of active species during the polymerization. The molecular weight and molecular weight distribution can be well controlled, implying synthesis of well-defined block structures of the copolymers. The chemical structures of block copolymers have been characterized by ¹H NMR, UV-vis, and photoluminescence (PL) spectra. PF aggregates are formed in water with the increase of temperature for the conjugated-ionic diblock copolymer synthesized, as confirmed by dynamic light scattering (DLS). The formation of excimers within the PF aggregates results in improved Förster resonance energy transfer (FRET) efficiencies.     

Synthesis and properties of the water-soluble self-acid-doped polypyrrole: poly[4-(3-pyrrolyl)butanesulfonic acid]

The water-soluble polypyrrole, poly[4-(3-pyrrolyl)butanesulfonic acid] (P3PyBSH), in which the β-position of pyrrole ring is substituted with n-butanesulfonic acid group, is synthesized by oxidation polymerization of 3PyBSNa followed with an ion-exchange of Na⁺ with H⁺. It can be cast into free-standing film from its aqueous solution and has a conductivity of 4.0×10⁻⁴ S/cm, higher than that of its sodium salt (5.5× 10⁻⁶ S/cm) by about 2 orders. The increase in conductivity is attributed to the self-doping by the protons originally on the side chains as supported by the absence of the anion FeCl₄ ⁻ (which generates during the polymerization) and the presence of polaron and bipolaron characteristics in its UV-Vis and IR spectra.     

A fluorescence sensor based on chiral polymer for highly enantioselective recognition of phenylalaninol

The chiral polymer P-1 incorporating (S)-2,2′-binaphthol (BINOL) and (S)-2,2′-binaphthyldiamine (BINAM) moieties in the main chain of the polymer backbone was synthesized by the polymerization of (S)-6,6′-dibutyl-3,3′-diformyl-2,2′-binaphthol (S-M-1) with (S)-2,2′-binaphthyldiamine (S-M-2) via nucleophilic addition-elimination reaction, and the chiral polymer P-2 could be obtained by the reduction reaction of P-1 with NaBH₄. The fluorescence intensity of the chiral polymer P-1 exhibits gradual enhancement upon addition of (d)- or (l)-phenylalaninol and keeps nearly a linear correlation with the concentration molar ratios of (d)- or (l)-phenylalaninol. The value of enantiomeric fluorescence difference ratio (ef) is 6.85 for the chiral polymer on (d)-phenylalaninol. On the contrary, the chiral polymer P-2 shows no obvious fluorescence response toward either (d)- or (l)-phenylalaninol.     

Self-diffusion of poly(p-phenyleneethynylene)s in dilute solution determined by pulsed-field-gradient NMR

Self-diffusion of poly[(2,5-didodecyl-p-phenylene)ethynylene]s (didodecyl-PPE) was measured in dilute CDCl₃ by pulsed-field-gradient NMR spectroscopy. The reduced versions of these didodecyl-PPEs, poly[2,5-didodecyl-p-xylylene]s (didodecyl-PPX), were also examined as random-coil analogs of equivalent chain lengths (14-120 repeat units). The coefficients for infinite-dilution self-diffusion (D₀) and their concentration dependence (k_F) were determined from plots of the self-diffusion coefficients versus concentration. These quantities were fit to power laws with molecular weight (M₀) and their scaling constants determined from double-logarithmic plots. For didodecyl-PPX, D₀ scales with M₀ by −0.50±0.03 (ν) and k_F scales with M₀ by 0.51±0.08 (α), consistent with a random-coil conformation for this polymer in solution. For didodecyl-PPE, D₀ scales with M₀ by −0.71±0.06 (ν) and k_F scales with M₀ by 0.96±0.06 (α), indicative of a semiflexible rod-like macromolecule.     

A ratiometric fluorescent sensor for zinc(II) with high selectivity

Spectroscopic studies revealed that the compound [N,N′-di(quinoline-2-methylene) -1,2-phenylenediimine] (1) exhibited a rather high selectivity toward Zn²⁺ over other metal ions, even Cd²⁺. In acetonitrile, the red shift of fluorescent emission from 396 nm to 426 nm upon zinc binding is due to the formation of a 1:1 metal/ligand complex.     

A turn-on fluorescent solid-sensor for Hg(II) detection

A rhodamine organosilane derivative (Rh-UTES) has been obtained by one-pot synthesis. The chemical structure of Rh-UTES was confirmed by nuclear magnetic resonance (NMR) and infrared (FTIR) techniques. To obtain an inorganic-organic hybrid sensor, Rh-UTES was covalently immobilized on a porous silicon microcavity (PSiMc) via triethoxysilane groups. The attachment of the organic derivative into PSiMc was confirmed by FTIR, specular reflectance, and scanning electron microscopy (SEM). The optical performance of Rh-UTES receptor for Hg²⁺ detection was investigated by fluorescent spectroscopy and microscopy. Upon the addition of increasing amounts of Hg²⁺ ions, a remarkable enhancement in emission intensity was produced in both systems. In the solid phase, an increase of integrated fluorescent emission of 0.12- and 0.15-fold after Hg²⁺ receptor coordination was observed. The light harvesting capability of PSiMc devices allowed obtaining an enhanced fluorescent emission after Rh-UTES immobilization (277-fold). The fluorescence microscopy of hybrid PSiMc sensor provided an optical qualitative test for Hg²⁺ detection.     

A highly selective turn-on sensor for Hg2 + based on a phosphorescent iridium (III) complex

A highly selective phosphorescent chemosensor for Hg^2 + based on the iridium (III) complex Ir(DTBT)₂(acac) (DTBT = 2-(5-(1,2 dihydroacenaphthylen-5-yl)thiophen-2-yl)benzothiazole, acac = acetylacetone) was synthesized and characterized. Ir(DTBT)₂(acac) exhibited relatively weak fluorescenceat at about 700 nm. Ir(DTBT)₂(acac) displayed a dramatic color change from near-infrared to yellow-green with the addition of Hg^2 +. More significantly, the chemosensor performed “turn-on” phosphorescent responses toward Hg^2 +.     

Incorporation of polyfluorenes into poly(lactic acid) films for sensor and optoelectronics applications

Films of neat and plasticized biodegradable poly(lactic acid) (PLA) matrices containing anionic conjugated polyelectrolytes, poly[9,9‐bis(4‐phenoxybutylsulfonate)]fluorene‐2,7‐diyl‐alt‐arylenes, with 1,4‐phenylene and 4,4″‐p‐terphenylene, respectively, as arylene groups or a neutral poly(9,9‐dialkylfluorene) for comparison were prepared by solution casting. These films were characterized using differential scanning calorimetry, thermogravimetry, scanning electron microscopy and fluorescence spectroscopy. In addition, the effects of plasticizer on the thermal properties and the oxygen permeability of the PLA films were measured through the oxygen transmission rate. Results show that it is possible to obtain thin, optically transparent and luminescent films with potential in oxygen sensing, exhibiting good thermal and photochemical stability. At high polyelectrolyte content, evidence is found for phase separation and aggregate formation and it is no longer possible to obtain completely homogeneous films. The possibility of incorporating the cationic metal complex tris(2,2′‐bipyridyl)ruthenium(II) into plasticized PLA films containing conjugated polyelectrolytes for dual‐wavelength ratiometric luminescence sensing is also discussed. Copyright © 2012 Society of Chemical Industry     

Measurement of the electrochemical response time and electron paramagnetic resonance behavior of poly(o‐phenetidine)–poly(styrene sulfonic acid) and poly(2‐ethylaniline)–poly(styrene sulfonic acid) complexes

Two studies were mainly focused on the measurement of electrochemical response time and the electron paramagnetic resonance (EPR) of the substituted polyaniline (PANI) complexes poly(o‐phenetidine) (POP)–poly(styrene sulfonic acid) (PSSA) and poly(2‐ethylaniline) (P2E)–PSSA, which were prepared by the electrochemical polymerization of the monomer (o‐phenetidine or 2‐ethylaniline) with PSSA, with indium tin oxide (ITO) as a working electrode in a 1M HCl solution. Ultraviolet–visible spectra measurements showed evidence for the doped substituted PANI system to have a highly electrochemical response time recorded at a temperature of 298 K, and the results were further analyzed on the basis of the color–discolor model, which is typical of protonation systems. At the reaction time (3 s) and monomer concentration (0.6M) with PSSA (0.15 μ), the best electrochemical color/discolor time of the POP–PSSA complexes was 125/125 ms (thickness = 3.00 μm), which was faster than that of the P2E–PSSA complexes. At the same thickness (10 μm), the best electrochemical color/discolor time of the POP–PSSA complexes was 500/250 ms, which was faster than the P2E–PSSA complexes (750/500 ms). With regard to film growth rate, the POP–PSSA complexes (1.0 μm/s) were faster than the P2E–PSSA complexes (0.79 μm/s); this was attributed to the substituted PANI having a steric effect and to good reactivity by the ethoxy group (? OC₂H₅) in the molecules. The EPR spectra of the two samples were recorded both at 298 and 77 K and were further analyzed on the basis of the polaron–bipolaron model. The narrower line width of the substituted PANI complexes arose due to polarons; that is, we propose that charge transport took place through both polarons and bipolarons. Compared to their salts, this could be attributed to the lower degree of structural disorder, the oxygen absorption on the molecules, and the steric effect by the side chain group. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1211–1221, 2005     

A water-soluble,low-cytotoxic and sensitive fluorescent probe based on poly(ethylene glycol) for detecting sulfide anion in aqueous media and imaging inside live cells

Sulfide anions are generated not only as a byproduct from industrial processes but also in biosystems. Hence, fluorescent probes for detecting sulfide anion which are water soluble, sensitive, selective and biocompatible are highly sought-after. In this study, we report a water-soluble, low-cytotoxic and sensitive fluorescent sensor for detecting sulfide anion. In this probe, the strong electron-withdrawing dinitrobenzenesulfonate ester group is incorporated onto fluorescein fluorophore, and correspondingly the fluorescence of fluorescein is efficiently quenched; while when the dinitrobenzenesulfonate ester is cleaved by the nucleophilic sulfide anion, the substantial fluorescence enhancement can be observed. Furthermore, poly(ethylene glycol) is coupled onto the fluorophore to impart the probe water-soluble and low cytotoxicity. The probe is capable of permeating the cell membrane and realizing sulfide anion monitoring and imaging in live cells and real sample. This technically-simple modification strategy may be suitable for fabricating some other fluorescent probes with enhanced biocompatibility and water solubility.     

Cationic phenyl-substituted poly(p-phenylenevinylene) related copolymers with efficient photoluminescence and synthetically tunable emissive colors

A series of amino-functionalized phenyl-substituted poly(p-phenylenevinylene) (PPV) related copolymers were synthesized by Wittig reaction. Their corresponding cationic conjugated polymers were successfully obtained via a post-polymerization approach. On the basis of FT-IR and ¹H NMR spectra, it was found that phenyl-substituted PPV related copolymers containing alkoxylated benzene (neutral polymer P1 and quaternized polymer P1′), phenylated benzene (neutral polymer P2 and quaternized polymer P2′) and fluorene (neutral polymer P3 and quaternized polymer P3′) moieties are of 55, 80, and 45% cis-vinylic linkage respectively while the polymer containing thiophene moiety (neutral polymer P4 and quaternized polymer P4′) is primarily of trans-vinylic linkage. Their photoluminescence (PL) were conveniently tuned from blue color to yellow color by introducing units with different optoelectronic properties into the PPV backbones. The polymer with fluorene unit and bulky phenylene-substituted benzene unit in the backbone exhibited the highest PL efficiency among these neutral and quaternized PPVs. P4′ containing little cis-vinylic linkage showed complete quenching while P1′-P3′ containing much more cis-vinylic linkage showed incomplete quenching, indicating that the quenching behavior of these cationic PPVs may be highly influenced by the content of cis-vinylic linkage in the PPV backbones.     

A naphthalimide-rhodamine ratiometric fluorescent probe for Hg based on fluorescence resonance energy transfer

On the basis of fluorescent resonance energy transfer from 1,8-naphthalimide to rhodamine B, a new fluorophore dyads (4) containing rhodamine B and a naphthalimide moiety was synthesized as a ratiometric fluorescent probe for detecting Hg²⁺ with a broad pH range 5.7-11.0. The selective fluorescence response of 4 to Hg²⁺ is due to the Hg²⁺-promoted desulfurization of the thiocarbonyl moiety, leading to the ring-opening of rhodamine B moiety of 4. When 4 was employed at 0.1 μM with the slit size being 20 nm/20 nm, a low level of Hg²⁺ (up to 3 × 10⁻⁸ M) can be detected using the system.     

Stimuli-induced core-corona inversion of micelles of water-soluble poly(sodium 2-(acrylamido)-2-methyl propanesulfonate-b-N-isopropylacrylamide)

Micelles of poly(sodium 2-(acrylamido)-2-methylpropanesulfonate-b-N-isopropylacrylamide) (PAMPS-b-PNIPAM) have been investigated in aqueous solutions using various techniques including dynamic light scattering, scanning electron microscopy, transmission electron microscopy and ζ-potential measurements. It was found that PAMPS-b-PNIPAM produces two distinct types of micelle structures; one is a PAMPS-core/PNIPAM-corona structure and the other is a PNIPAM-core/PAMPS-corona structure. The PAMPS-core micelle with the PNIPAM-corona was obtained by insolubilizing the PAMPS block with ferric ion (Fe³⁺) at room temperature, and the PNIPAM-core micelle with the PAMPS-corona was obtained by increasing the solution temperature above the lower critical solution temperature (LCST) of the PNIPAM block in the absence of the Fe³⁺ ion. We have also found that the inversion from one type to the other is reversible. The transformation from the PAMPS-core micelle to the PNIPAM-core micelle was induced by removing Fe³⁺ ion using ethylenediaminetetraacetic acid followed by elevating the temperature above the LCST of the PNIPAM block, while the reverse transformation was triggered by adding Fe³⁺ ion at a lower temperature.     

Butyl pyrene containing poly(arylene ethynylene)s for highly sensitive and selective sensing of TNT

A series of poly(arylene ethynylene)s (PAEs) containing ^tbutyl pyrene in the main chain were synthesized for nitroaromatic sensors. As control, similar polymers containing unsubstituted pyrene were also synthesized. The sensory properties of the polymers were studied towards various nitroaromatic compounds like trinitrotoluene (TNT), dinitrotoluene (DNT), nitrotoluene (NT), nitrobenzene (NB) and picric acid (PA) in solution as well as vapor state. Interestingly, all the ^tbutyl substituted pyrene containing polymers showed higher sensitivity than the corresponding unsubstituted pyrene containing polymers. Moreover, the polymers showed high sensitivity towards TNT as compared to the other nitroaromatic compounds. The sensitivity of one of the polymer PB was found several folds higher than that of the similar reported polymer containing unsubstituted pyrene ring. In addition, ^tbutyl pyrene containing polymers were found to have improved molecular weight, thermal stability, fluorescence quantum yield, film forming properties and solubility in common organic solvents as compared to the control polymers.