Optimization of the Molecular Orbital Energies of Conjugated Polymers for Optical Amplification of Fluorescent Sensors

Enhancing Optoelectronic Anisotropy in Highly Oriented Thin Films by Fluorine Substitution in Novel Semiconducting Polymers

The recent past has witnessed remarkable progress in organic electronics, driven by the quest for flexible, lightweight, and cost-effective electronic devices. Semiconducting polymers (SCPs) have emerged as key materials in this field, offering unique electronic and optoelectronic properties along with mechanical flexibility. This study focuses on designing, synthesizing, and utilizing novel donor-acceptor (D-A) copolymer-based SCPs introducing a difluorothiophene moiety in the polymeric backbone. The importance of fluorine substitution for backbone planarity was verified by density functional theory calculations, comparing it with a nonfluorine substituted counterpart. Through the Unidirectional Floating Film Transfer Method (UFTM), we fabricated highly oriented thin films, resulting in increased optical anisotropy with dichroic ratios reaching 19.3 in PC20-FT thin films, one of the highest optical anisotropy observed for solution processable SCP thin films. X-ray diffraction and atomic force microscopy results validated the increase in the crystallinity and domain size with the increasing alkyl chain length. Finally, we elucidate these findings in the context of electrical applications by fabricating organic field-effect transistors revealing anisotropic charge transport achieving a promising mobility of 1.24 cm2V-1s-1 and mobility anisotropy of 39.5. This study offers insights into the design principles and performance optimization of SCP-based devices, paving the way for advancements in plastic electronics.

Ultrabright Pdots with a Large Absorbance Cross Section and High Quantum Yield

Semiconducting polymer dots (Pdots) are increasingly used in biomedical applications due to their extreme single-particle brightness, which results from their large absorption cross section (σ). However, the quantum yield (Φ) of Pdots is typically below 40% due to aggregation-induced self-quenching. One approach to reducing self-quenching is to use FRET between the donor (D) and acceptor (A) groups within a Pdot; however, Φ values of FRET-based Pdots remain low. Here, we demonstrate an approach to achieve ultrabright FRET-based Pdots with simultaneously high σ and Φ. The importance of self-quenching was revealed in a non-FRET Pdot: adding 30 mol % of a nonabsorbing polyphenyl to a poly(9,9-dioctylfluorene) (PFO) Pdot increased Φ from 13.4 to 71.2%, yielding an ultrabright blue-emitting Pdot. We optimized the brightness of FRET-based Pdots by exploring different D/A combinations and ratios with PFO and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-phenylene)] (PFP) as donor polymers and poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-(1,4-phenylene)] (PFPV) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1',3}-thiadiazole)] (PFBT) as acceptor polymers, with a fixed concentration of poly(styrene-co-maleic anhydride) as surfactant polymer. Ultrabright blue-emitting Pdots possessing high Φ (73.1%) and σ (σ_R = σ_abs/σ_all, 97.5%) were achieved using PFP/PFPV Pdots at a low acceptor content (A/[D + A], 2.5 mol %). PFP/PFPV Pdots were 1.8 times as bright as PFO/PFPV Pdots due to greater coverage of acceptor absorbance by donor emission─a factor often overlooked in D/A pair selection. Ultrabright green-emitting PFO Pdots (Φ = 76.0%, σ_R = 92.5%) were obtained by selecting an acceptor (PFBT) with greater spectral overlap with PFO. Ultrabright red-emitting Pdots (Φ = 64.2%, σ_R = 91.0%) were achieved by blending PFO, PFBT, and PFTBT to create a cascade FRET Pdot at a D:A₁:A₂ molar ratio of 61:5:1. These blue, green, and red Pdots are among the brightest Pdots reported. This approach of using a small, optimized amount of FRET acceptor polymer with a large donor-acceptor spectral overlap can be generalized to produce ultrabright Pdots with emissions that span the visible spectrum.

Formation of Multicolor Nanogels Based on Cationic Polyfluorenes and Poly(methyl vinyl ether-alt-maleic monoethyl ester): Potential Use as pH-Responsive Fluorescent Drug Carriers

In this study, we employed the copolymer poly(methyl vinyl ether-alt-maleic monoethyl ester) (PMVEMA-Es) and three fluorene-based cationic conjugated polyelectrolytes to develop fluorescent nanoparticles with emission in the blue, green and red spectral regions. The size, Zeta Potential, polydispersity, morphology, time-stability and fluorescent properties of these nanoparticles were characterized, as well as the nature of the interaction between both PMVEMA-Es and fluorescent polyelectrolytes. Because PMVEMA-Es contains a carboxylic acid group in its structure, the effects of pH and ionic strength on the nanoparticles were also evaluated, finding that the size is responsive to pH and ionic strength, largely swelling at physiological pH and returning to their initial size at acidic pHs. Thus, the developed fluorescent nanoparticles can be categorized as pH-sensitive fluorescent nanogels, since they possess the properties of both pH-responsive hydrogels and nanoparticulate systems. Doxorubicin (DOX) was used as a model drug to show the capacity of the blue-emitting nanogels to hold drugs in acidic media and release them at physiological pH, from changes in the fluorescence properties of both nanoparticles and DOX. In addition, preliminary studies by super-resolution confocal microscopy were performed, regarding their potential use as image probes.

Bicolour fluorescent molecular sensors for cations: design and experimental validation

Molecular entities whose fluorescence spectra are different when they bind metal cations are termed bicolour fluorescent molecular sensors. The basic design criteria of this kind of compound are presented and the different fluorescent responses are discussed in terms of their chemical behaviour and electronic features. These latter elements include intramolecular charge transfer (ICT), formation of intramolecular and intermolecular excimer/exciplex complexes and Förster resonance energy transfer (FRET). Changes in the electronic properties of the fluorophore based on the decoupling between its constitutive units upon metal binding are also discussed. The possibility of generating fluorescent bicolour indicators that can capture metal cations in the gas phase and at solid-gas interfaces is also discussed.

Water-soluble oligofluorenes bearing N1-alkylcytosine side chains as turn-on and turn-off materials in telomere DNA length sensing

Water-soluble cationic and anionic oligofluorenes bearing N1-alkylcytosine side chains, namely OF-1 and OF-2, were synthesized. The photoluminescence (PL) intensity of an aqueous solution of OF-1 decreased on the addition of (TTAGGG)m as telomere DNA models. In contrast, the PL intensity of OF-2 increased on the addition of DNA.

Micellization-induced amplified fluorescence response for highly sensitive detection of heparin in serum

Fluorescence-based assays should be feasible in aqueous media for effectively detecting the biological factors. However, numerous sensors have limited signal transductions and low fluorescence quantum yields due to the ingerently reduced excited state energy of fluorophores in aqueous solution, which reduces their sensitivity. This necessitates a smart sensing approach with an amplified fluorescence response for analytes in aqueous solution. Herein, a new building block which self-assembles in aqueous media, giving a micellar sturcuture with the hydrophobic π-extended conjugated system at the core and hydrophilic groups at the periphery, was devised for the first time. We demonstrated that the aggregated fluorophores in a micelle induce amplified fluorescence quenching, in which the excited electron efficiently migrates through π-extended conjugated system in a micelle, as in a polymeric system. Such feature differentiates this sensing approach from the numerous fluorescence-based tools previously developed for sensitive detection. This new system exhibited highly sensitive signal transduction for specific analytes even under actual bioanalytical conditions.

A 2-(benzo[d]thiazol-2-yl)phenol based on conjugated polymer: Highly selective colorimetric fluorescent chemosensor for F-depending on Si–O bond cleavage reaction

Design and synthesis of highly selective fluorine ion probes become particularly important owing to the specific role of fluorine ion in chemical and biomedical progresses. As a new-type of fluorescent material, conjugated polymers with unique photometric properties have been widely researched by scientists in the field of the fluorescence sensors. In this study, the polymer PBTPV-OSi containing benzothiazole moiety is synthesized via palladium-catalyzed Heck coupling reaction. This polymer not only exhibits good solubility in organic solvents but also shows high selectivity for fluorine ion detection in comparison to other anions. Upon addition of F− to PBTPV-OSi solution, Si–O cleavage of PBTPV-OSi leads to the fluorescence quenching of the polymer in tetrahydrofuran dramatically, and the detection limit is 8 × 10−6 mol/L. Moreover, besides detecting fluorine ion from organic phase, the probe can also effectively detect potassium fluoride from inorganic phase. More importantly, a naked-eye detectable chromogenic and fluorogenic dual response to fluorine ion (F−) can be visibly noted and the detection process of fluorine ion is relatively fast.

Different phase-dominated chiral assembly of polyfluorenes induced by chiral solvation: axial and supramolecular chirality

The introduction of chirality in an achiral system will not only help avoid the tedious and expensive synthesis of chiral substances or catalysts but also greatly expand the ranges of chiral compounds. Herein, the induction of chirality in achiral polyfluorene (PF2/6 and PF8) with different alkyl chains at the C9 position of fluorene was achieved using a binary solvent system, in which ethanol was used as a poor solvent and chiral limonene was employed simultaneously as a good solvent and chiral solvent. The circular dichroism (CD), UV-vis and photoluminescence (PL) spectra demonstrated that the structures of PFs with linear/branched alkyl side chains and the volume fractions of the cosolvents had an obvious effect on the generation of chirality driven by chiral solvation. During the chiral assembly processes of PFs, PF8 with a linear alkyl side chain demonstrated the obvious chiral β phase, while PF2/6 with a branched alkyl side chain only showed the chiral α phase. WAXD data also confirmed the existence of quite different phases of PF8 and PF2/6. The first induced chirality of PF with a branched alkyl side chain (PF2/6) will help the further understanding of the chiral assembly mechanism of PFs driven by chiral solvation. The induced chirality of PF2/6 was axial chirality of the PF chain but the chirality of PF8 was from the supramolecular chiral assembly of the PF chains. The linear dependence of the maximum CD and g_CD values on the enantiomeric purity of chiral limonene demonstrated that the achiral PFs have a potential application as chiral sensors to detect the ee value of limonene.

The chiral solvation induced chirality in achiral polyfluorenes showed the axial chirality for PF2/6 with branched side alkyl chain, but supramolecular chirality for PF8 with linear side alkyl chain.

Ultrabright Fluorescent Silica Nanoparticles Embedded with Conjugated Oligomers and Their Application in Latent Fingerprint Detection

Fluorescent micro- and nanosized particles have a broad range of applications in biology, medicine, and engineering. For these uses, the materials should have high emission efficiency and good photostability. However, many organic fluorophores suffer from aggregation-induced quenching effects and photobleaching. Here, we used a simple method based on covalently blending a fluorescent conjugated oligomer with silica nanoparticles to achieve emission quantum yields as high as 97%. The resulting system also showed excellent stability under continuous light illumination, in a range of pH values and temperatures, and in common solvents. This fluorescent material showed outstanding properties, including highly efficient blue emission, low cost, low toxicity, and easy synthesis. Furthermore, its effectiveness for latent fingerprint detection was demonstrated as a proof of concept on various substrates. The obtained emissive fingerprint powder gave good optical/fluorescent images with high contrast and resolution between the ridges and spaces.

A Conjugated Polyelectrolyte with Pendant High Dense Short-Alkyl-Chain-Bridged Cationic Ions: Analyte-Induced Light-Up and Label-Free Fluorescent Sensing of Tumor Markers

A novel cationic water-soluble conjugated polyelectrolyte (CPE) of polyfluorene that contains 15% fraction of 2,1,3-benzothiadiazole (BT) units (PFC3NBT) has been obtained. PFC3NBT demonstrates intramolecular energy transfer from the fluorene segments to BT sites when negatively charged species (SDS or DNAs) are added, following by a shift in emission color from blue to green, has been developed. The high density of positive charges and pendent short alkyl chains of N-propyltrimethylammoniums endow PFC3NBT with high solubility and high fluorescence quantum efficiency of 33.6% in water. The fluorescence emission properties were investigated in the presence of adverse buffer solutions, different surfactants and DNA strands. Interesting fluorescence emission quenching at short wavelength and fluorescence resonance energy transfer (FRET) induced light-on at BT sites were observed and discussed in detail. Very different from previous reports, the fluorescence emission spectra transition happens with an enhancement of integrated fluorescent intensity. The analytes induced a light-up sensing system was studied with a PFC3NBT/SDS complex mode and confirmed with DNA/DNA-FAM sensing systems. More exciting preliminary results on label-free sensing of tumor markers were also reported by investigating the unique fluorescence response to 11 kinds of proteins. These results provide a new insight view for designing CPEs with light-up and label-free features for biomolecular sensing.

Cationic Polythiophenes as Gene Delivery Enhancer

There is urgent demand of easily available and highly effective method to improve transgene performance of polymeric gene carriers at low consumption of delivery materials. We developed biocompatible multicomponent nanocomposites in which small quantities of cationic polythiophenes were engineered into the outer shell of polypeptide/DNA polyplexes without covalent linkages. We revealed the introduction of polythiophenes in small quantities led to multiple outcomes including modulation of polyplex size and zeta potential, increase in polyplex stability, promotion of endolysosome membrane disruption, light-induced generation of reactive oxygen species (ROS), and significant enhancement of gene delivery to tumor cells. The factors such as structural architectures, molecular weights, photosensitizing capability, and percentage composition of polythiophenes were investigated.

Facile Fabrication of AIE-Active Fluorescent Polymeric Nanoparticles with Ultra-Low Critical Micelle Concentration Based on Ce(IV) Redox Polymerization for Biological Imaging Applications

Fluorescent polymeric nanoparticles (FPNs) with aggregation-induced emission (AIE) property have received increasing attention and possess promising biomedical application potential in the recent years. Many efforts have been devoted to the fabrication methodologies of FPNs and significant advance has been achieved. In this contribution, a novel strategy for the fabrication of AIE-active amphiphilic copolymers is reported for the first time based on the Ce(IV) redox polymerization. As an example, ene group containing AIE-active dye (named as Phe-alc) is directly grafted onto a water soluble polymer polyethylene glycol (PEG) in H₂ O/THF system under low temperature. Thus-obtained amphiphilic fluorescent polymers will self-assemble into FPNs with ultra-low critical micelle concentration, ultra-brightness, and great water dispersibility. Biological evaluation results suggest that the PEG-poly(Phe-alc) possess excellent biocompatibility and can be used for tracing their behavior in cells using confocal laser scanning microscope. These features make PEG-poly(Phe-alc) FPNs promising candidates for many biomedical applications, such as cell imaging, drug delivery vehicles, and targeted tracing. More importantly, many other functional groups can also be incorporated into these AIE-active FPNs through the redox polymerization. Therefore, the redox polymerization should be a facile and effective strategy for fabrication of AIE-active FPNs.

Reaction-based conjugated polymer fluorescent probe for mercury(ii): good sensing performance with “turn-on” signal output

Based on a Hg²⁺-promoted deprotection reaction of dithioacetal, the conjugated polymer PDT showed high sensitivity with the detection limit of 1.0 × 10⁻⁶ mol L⁻¹ and 1 × 10⁻⁵ mol L⁻¹ in solution and as test strips, respectively.

Novel Visible-Light Photodetector Based on Two-Dimensional Confined Electron Donor-Acceptor Co-Assembled Layered Double Hydroxide Ultrathin Films

Photodetectors are a class of critical optoelectronic devices that can transform incident light into a detectable electrical signal. In this work, we develop a novel photodetector based on two-dimensional (2D) confined electron donor-acceptor co-assembled ultrathin films (UTFs). The (PCDTBT@CN-PPV/LDHs) _n UTFs are composed of an organic electron donor, poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT), and an acceptor, poly(5-(2-ethylhexyloxy)-2-methoxy-cyanoterephthalylidene) (CN-PPV), within inorganic Mg₂Al-layered double hydroxides (LDHs). The UTFs exhibit broad-range visible-light absorption, from 400 to 650 nm, resulting from complementary absorption of PCDTBT and CN-PPV. The fluorescence emission of the UTFs is completely quenched, implying the occurrence of photoinduced charge transfer (PCT). As a novel photodetector, the co-assembled UTFs have a high photocurrent and on/off switching ratio (300 nA/∼120), in contrast to those of the PCDTBT/CN-PPV drop-casting thin film (5.4 nA/∼1.6); a fast response; a short recovery time (lower than 0.1 s); and excellent wavelength and light-intensity dependence. The PCT mechanism can be attributed to the formation of a 2D bulk heterojunction of the two polymers within the interlayers of the LDH nanosheets. Furthermore, flexible UTFs on polyethylene terephthalate substrates are also fabricated, which exhibit excellent folding strength and electrical stability.

Ratiometric Array of Conjugated Polymers-Fluorescent Protein Provides a Robust Mammalian Cell Sensor

Supramolecular complexes of a family of positively charged conjugated polymers (CPs) and green fluorescent protein (GFP) create a fluorescence resonance energy transfer (FRET)-based ratiometric biosensor array. Selective multivalent interactions of the CPs with mammalian cell surfaces caused differential change in FRET signals, providing a fingerprint signature for each cell type. The resulting fluorescence signatures allowed the identification of 16 different cell types and discrimination between healthy, cancerous, and metastatic cells, with the same genetic background. While the CP-GFP sensor array completely differentiated between the cell types, only partial classification was achieved for the CPs alone, validating the effectiveness of the ratiometric sensor. The utility of the biosensor was further demonstrated in the detection of blinded unknown samples, where 121 of 128 samples were correctly identified. Notably, this selectivity-based sensor stratified diverse cell types in minutes, using only 2000 cells, without requiring specific biomarkers or cell labeling.

Anionic conjugated polytriazole: direct preparation, aggregation-enhanced emission, and highly efficient Al3+ sensing

AEE-active anionic conjugated polytriazole was directly prepared by Cu(i)-catalyzed click polymerization, which could be used to specifically and sensitively detect Al³⁺.

Tetrathiafulvalene Vinylogue-Fluorene Co-oligomers: Synthesis, Properties, and Supramoleclar Interactions with Carbon Nanotubes

A series of bis(dithiafulvenyl)-end-capped fluorene derivatives was prepared and subjected to a one-pot iodine-promoted oxidative polymerization to yield π-conjugated co-oligomers containing tetrathiafulvalene vinylogue and fluorene repeat units. The resulting π-oligomers were characterized to take either acyclic or cyclic molecular structures, depending on the π-conjugation length of the monomer used for the polymerization. Electronic and electrochemical redox properties were examined by UV-vis spectroscopic and cyclic voltammetric analyses, while the supramolecular interactions of the π-oligomers with single-walled carbon nanotubes were investigated by UV-vis-NIR and Raman spectroscopy.

An Inexpensive Co-Intercalated Layered Double Hydroxide Composite with Electron Donor-Acceptor Character for Photoelectrochemical Water Splitting

In this paper, the inexpensive 4,4-diaminostilbene-2,2-disulfonate (DAS) and 4,4-dinitro-stilbene-2,2- disulfonate (DNS) anions with arbitrary molar ratios were successfully co-intercalated into Zn₂Al-layered double hydroxides (LDHs). The DAS(50%)-DNS/LDHs composite exhibited the broad UV-visible light absorption and fluorescence quenching, which was a direct indication of photo-induced electron transfer (PET) process between the intercalated DAS (donor) and DNS (acceptor) anions. This was confirmed by the matched HOMO/LUMO energy levels alignment of the intercalated DAS and DNS anions, which was also compatible for water splitting. The DAS(50%)-DNS/LDHs composite was fabricated as the photoanode and Pt as the cathode. Under the UV-visible light illumination, the enhanced photo-generated current (4.67 mA/cm² at 0.8 V vs. SCE) was generated in the external circuit, and the photoelectrochemical water split was realized. Furthermore, this photoelectrochemical water splitting performance had excellent crystalline, electrochemical and optical stability. Therefore, this novel inorganic/organic hybrid photoanode exhibited potential application prospect in photoelectrochemical water splitting.

Water-soluble conjugated polymers as active elements for organic nonvolatile memories

Memory devices based on three water-soluble donor–acceptor conjugated polymers were fabricated from aqueous solution, and show excellent memory performance.

Synthesis and spectral characterization of photoswitchable oligo(p-phenylenevinylene)–spiropyran dyad

A novel dyad molecule coupling oligo(p-phenylenevinylene) (OPV) with spiropyran (SP) was synthesized and characterized in solution and in solid phase. Light-driven reversible transformations between isomers ofSPmodulate the fluorescence ofOPV.

Synthesis and chemosensory application of water-soluble polyfluorenes containing carboxylated groups

Detection of metal ions in aqueous solutions is a major issue for environmental protection. Conjugated polyelectrolytes showing high sensitivity and selectivity towards the detection of metal ions are highly desirable. We report a water-soluble polyfluorene containing carboxylated groups (P1), poly[9,9'-bis(3''-propanoate)fluoren-2,7-yl] sodium salt, which shows high recognition capability toward Cu(+) and Cu(2+). P1 was prepared via the hydrolysis of poly[9,9'-bis(tert-butyl-3''-propanoate)fluoren-2,7-yl] (P0) which was synthesized by Suzuki coupling polymerization. The photoluminescence (PL) spectra of P1 in aqueous solution are significantly quenched in the presence of Cu(+) and Cu(2+). P1 shows high selectivity and sensitivity toward Cu(+) and Cu(2+), with the Stern-Volmer constants (Ksv) being 3.5 × 10(6) and 5.78 × 10(6) M(-1), respectively. Moreover, the stoichiometric ratio of the P1 repeat unit to Cu(+) or Cu(2+) is 2 : 1 obtained from Job's plot. P1 maintains high selectivity towards Cu(+) or Cu(2+) in the presence of various metal cations. Our results demonstrate that P1 shows very high sensitivity and selectivity in recognizing Cu(+) and Cu(2+), indicating that it is a promising functional material for chemical sensors.

Fluorescent nanomicelles for selective detection of Sudan dye in Pluronic F127 aqueous media

Novel self-assembled water-soluble nanomicelles that contain fluorescent conjugated polymers (poly(9,9-dioctylfluorene) (PFO) or poly[2,7-(9,9-dihexylfluorene)-alt-4,4'-phenylether] (PF-PE)) have been obtained and used as the highly sensitive/selective platform for Sudan dye detection. The Fluorescent nanomicelles exhibited a highly selective fluorescence quenching by the prohibited food additive Sudan I, while not for the natural pigments: Capsanthin and Beta-carotene, due to the more suitable matching of the LUMOs (lowest unoccupied molecular orbital) of the conjugated polymers with that of Sudan I molecules. The Stern-Volmer constants (K(SV)) of PF-PE/F127 and PFO/F127 for Sudan I were 1,040,480 and 665,000 M(-1), respectively, which were more than 100 times higher than those of the same conjugated polymers in the orgainc solvents. The significantly enhanced sensitivity was due to the collective effect of the F127 micelles to both chromophore and analyte, through which the fluorophone-analyte binding interaction is significantly strengthened and efficient photoinduced charge transfer occurs. The as-proposed materials and approach may be potentially applied in the real-time food safety screening.

Hybrid silver nanoparticle/conjugated polyelectrolyte nanocomposites exhibiting controllable metal-enhanced fluorescence

Metal-enhanced fluorescence of conjugated polyelectrolytes (CPs) is realized using a simple, green hybrid Ag nanocomposite film. Ag nanoparticles (Ag NPs) are pre-prepared by sodium citrate reduction and incorporated into agarose by mixing to form an Ag-containing agarose film (Ag@agarose). Through variation of the amount of Ag NPs in the Ag@agarose film as well as the thickness of the interlayer between CPs and the Ag@agarose film prepared of layer-by-layer assembly of chitosan and sodium alginate, a maximum 8.5-fold increase in the fluorescence of CPs is obtained. After introducing tyrosinase, this system also can be used to detect phenolic compounds with high sensitivity and good visualization under ultraviolet light.

Selective Interaction of a Cationic Polyfluorene with Model Lipid Membranes: Anionic versus Zwitterionic Lipids

This paper explores the interaction mechanism between the conjugated polyelectrolyte {[9,9-bis(6'-N,N,N-trimethylammonium)hexyl]fluorene-phenylene}bromide (HTMA-PFP) and model lipid membranes. The study was carried out using different biophysical techniques, mainly fluorescence spectroscopy and microscopy. Results show that despite the preferential interaction of HTMA-PFP with anionic lipids, HTMA-PFP shows affinity for zwitterionic lipids; although the interaction mechanism is different as well as HTMA-PFP's final membrane location. Whilst the polyelectrolyte is embedded within the lipid bilayer in the anionic membrane, it remains close to the surface, forming aggregates that are sensitive to the physical state of the lipid bilayer in the zwitterionic system. The different interaction mechanism is reflected in the polyelectrolyte fluorescence spectrum, since the maximum shifts to longer wavelengths in the zwitterionic system. The intrinsic fluorescence of HTMA-PFP was used to visualize the interaction between polymer and vesicles via fluorescence microscopy, thanks to its high quantum yield and photostability. This technique allows the selectivity of the polyelectrolyte and higher affinity for anionic membranes to be observed. The results confirmed the appropriateness of using HTMA-PFP as a membrane fluorescent marker and suggest that, given its different behaviour towards anionic and zwitterionic membranes, HTMA-PFP could be used for selective recognition and imaging of bacteria over mammalian cells.

Aggregation-deaggregation-triggered, tunable fluorescence of an assay ensemble composed of anionic conjugated polymer and polypeptides by enzymatic catalysis of trypsin

We prepared a water-soluble conjugated polymer composed of electron-donating units and electron-accepting groups in the backbone. The polymer exhibits a short wavelength (blue) emission in aqueous solution and long wavelength (red) emission in the solid state, because of intermolecular energy transfer. Considering this, we develop a new approach for the sensitive detection of trypsin, which is known to control pancreatic exocrine function, using an ensemble system composed of the anionically charged conjugated polymer and cationically charged polypeptides (such as polylysine and polyarginine). The blue-emitting, water-soluble conjugated polymer becomes aggregated upon exposure to the polypeptides, leading to a red-emitting assay ensemble. The red-emitting assay ensemble becomes dissociated in the conjugated polymer and polypeptide fragments by selective degradation of trypsin, which then exhibits recovery of blue emission. This emission-tuning assay ensemble allows for detection of trypsin at nanomolar concentrations, which enables naked-eye detection. Importantly, this strategy can be employed for label-free, continuous assay for trypsin.

Self-assembled conjugated polymer/carboxymethyl chitosan grafted poly(p-dioxanone) nanomicelles and their use in functionalized indicator paper for fast and visual detection of a banned food dye

Fluorescent nanoparticles composed of a self-assembled polysaccharide derivative and a conjugated polymer show greatly improved sensitivity for the selective detection of a banned food dye in aqueous media.

π-Electron conjugation in two dimensions

Organic oligomers and polymers with extended π-conjugation are the fundamental building blocks of organic electronic devices. Novel routes are being explored to create tailor-made organic materials, and recent progress in organic chemistry and surface chemistry has led to the synthesis of planar 2D polymers. Here we show how extending π-conjugation in the second dimension leads to novel materials with HOMO-LUMO gaps smaller than in 1D polymers built from the same parent molecular repeat unit. Density functional theory calculations on experimentally realized 2D polymers grant insight into HOMO-LUMO gap contraction with increasing oligomer size and show fundamental differences between 1D and 2D "band gap engineering". We discuss how the effects of cross-conjugation and dihedral twists affect the electronic gaps.

Cell imaging and DNA delivery in fibroblastic cells by conjugated polyelectrolytes

This study concentrates on the potential application of conjugated polyelectrolytes (CPEs) to cell imaging and DNA delivery. Four different types of polyfluorene copolymers, namely, PAHFP-Br, PAEFP-Br, PAHFbT-Br, and PSBFP-Na, which have the same π-conjugated backbone but different side chains, were synthesized. For cytotoxicity testing, L-929 fibroblastic cells were treated with increasing concentrations (0-50 µM) of each CPE and then cell viability was determined by WST-8 assay. Cellular uptake of CPEs into cultured L-929 cells was observed by fluorescence microscopy. To examine DNA delivery by CPEs, the cells were incubated for 1 H with PAHFP-Br/fluorescein (Fl)-labeled single-stranded DNA (ssDNA-Fl) complex and then visualized by fluorescence microscopy. Cytotoxicity of CPEs was increased in a dose-dependent manner but at lower than 10 µM, PAHFP-Br, PAEFP-Br, and PSBFP-Na did not show any cytotoxic effects on the cells. When added to cell cultures at 1 µM, PAHFP-Br/ssDNA-Fl complex was delivered and then dissociated into PAHFP-Br and ssDNA-Fl within the cells. This result implies that PAHFP-Br can enable cell imaging and DNA delivery into fibroblastic cells. Therefore, it is suggested that PAHFP-Br with various advantages such as low cytotoxicity and high fluorescence efficiency can be extensively used as a potential agent for cell imaging and gene delivery.

Stabilization of neutral polyfluorene in aqueous solution through their interaction with phospholipids and sol-gel encapsulation

Interaction between poly[9,9-bis(6'-bromohexyl)-2,7-fluorene-co-alt-1,4-phenylene] (PFPBr2), a neutral conjugated polyfluorene which is completely insoluble in water, and zwitterionic phospholipids has been investigated in order to generate new fluorescent structures which are stable in aqueous media as a means of extending the biological applications of these kinds of polymers. Two types of differently shaped and composed fluorescent structures were identified and then isolated and characterized separately using different biophysical techniques. The first structure type, corresponding to liposomal complexes, showed a fluorescence band centered around 405 nm and maximum absorption at 345 nm, while the second, corresponding to polymer-phospholipid aggregates of variable sizes with lower lipid content, absorbed at longer wavelengths and displayed a well resolved fluorescence spectrum with a maximum centered at 424 nm. Both structures were stable in a large range of pH, and their fluorescence intensity remained practically unaltered for 10 days; it then began to decrease, which was probably because of aggregation. Encapsulation of these structures within the pores of a sol-gel matrix did not affect their fluorescent properties but increased their stability, avoiding further aggregation and subsequent precipitation.

Conjugated polymer amplified far-red/near-infrared fluorescence from nanoparticles with aggregation-induced emission characteristics for targeted in vivo imaging

Fluorescence-amplified far-red/near-infrared (FR/NIR) nanoparticles (NPs) are synthesized by co-encapsulation of conjugated polymer donor (poly[9,9-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)fluorenyldivinylene]; PFV) and a fluorogen acceptor (2-(2,6-bis((E)-4-(phenyl(4'-(1,2,2-triphenylvinyl)-[1,1'-biphenyl]-4-yl)amino)styryl)-4H-pyran-4-ylidene)malononitrile; TPE-TPA-DCM) with aggregation-induced emission (AIE) characteristics using biocompatible bovine serum albumin (BSA) as the encapsulation matrix. The good spectral overlap and close proximity between PFV and TPE-TPA-DCM in BSA NPs result in a 5.3-fold amplified TPE-TPA-DCM emission signal via fluorescence resonance energy transfer (FRET). The obtained PFV/TPE-TPA-DCM co-loaded BSA NPs are spherical in shape with a large Stokes shift of ∼223 nm and low cytotoxicity. The BSA matrix allows further functionalization with arginine-glycine-aspartic acid (RGD) peptide to yield fluorescent probes for specific recognition of integrin receptor-overexpressed cancer cells. The advantage of PFV amplified FR/NIR signal from TPE-TPA-DCM is further demonstrated in cellular and in vivo imaging using HT-29 colon cancer cells and a murine hepatoma H22 tumor-bearing mouse model, respectively. The high FR/NIR fluorescence and specific cancer targeting ability by RGD surface functionalization make the PFV/TPE-TPA-DCM co-loaded BSA-RGD NPs a unique FR/NIR fluorescent probe for cellular imaging and in vivo tumor diagnosis in a high contrast and selective manner.