Fluorescence Intensity Of Polymer Research Articles

Fluorescent cholesteric liquid crystal polymers with dual properties: design, synthesis and characterisation

ABSTRACT In this study, we have synthesised fluorescent liquid crystal polymers with good fluorescence and optical properties through effective molecular design. Firstly, two series of cholesteric liquid crystal polymers (PN and PS series) were prepared by graft copolymerisation of cholesteric monomer(N1), monomer containing cyanobiphenyls with different length of carbon-chain (N2 and N3) and monomer containing bromine (6-Br) with polymethylhydrosiloxane chain as the polymer backbone. Secondly, we obtained fluorescent polymers RPN and RPS series by etherification reaction of PN and PS series with fluorescent monomer (F). The molecular structures and mesomorphic behaviour of monomers and polymers were characterised by usual ways. All the polymers are confirmed to consist with molecular design. The fluorescence of the polymers was investigated by fluorescence spectroscopy and fluorescent images. The fluorescence intensity of polymers is highly dependent on temperature. Fluorescent cholesteric liquid crystal polymers emitted different intensity fluorescence under ultraviolet irradiation and some regularities were summarised. RPN series with short carbon-chain meets our expectations for performance with dual effects of fluorescence and selective reflection, which were well verified. The effect of monomers with different chain lengths on the properties of fluorescent polymers has been described.

Initial evaluation of six different brown algae species as source for crude bioactive fucoidans

The fucose-containing sulfated polysaccharides (syn. fucoidans) from brown seaweeds exhibit multiple biological activities. The aim of the present study was to evaluate the suitability of crude fucoidans from six different brown algal species for further research and development. For this, fucoidans were extracted from Fucus vesiculosus (F.v.), F. serratus (F.s.), F. evanescens (F.e.), Dictyosiphon foeniculaceus (D.f.), Laminaria digitata (L.d.), and Saccharina latissima (S.l.) and compared concerning their yields, their basic characteristics, degree of sulfation (DS), molecular mass, monosaccharide composition, their contents of polyphenols, laminarin and protein as well as their radical-scavenging capacity, three exemplary bioactivities and their fluorescence intensity (FI) increasing effect on the sulfated glycan sensor Polymer-H. The activities positively correlated with the DS, fucose content and the FI of Polymer H, whereas the antioxidant capacity correlated with the coextracted polyphenols. The best predictive power for the activities showed to have the combination of FI of Polymer-H and DS, which can thus be used for an initial screening of algae extracts. D.f. turned out to be unsuitable as fucoidan source, as the extract had only a low DS (0.14) and fucose content (38.7%) as well as the weakest bioactivities. The fucoidans from S.l. and F.e., which had the fucose content, highest DS, purity and yield, exhibited the best activities and thus proved to be the fucoidans most suitable for further investigations.

How to Design Donor-Acceptor Based Heterocyclic Conjugated Polymers for Applications from Organic Electronics to Sensors.

Over the past few years, significant progress has been made in the design of organic semi-conducting conjugated polymers that readily transport holes or electrons and can result in light emission. The conjugated backbone consist mainly of electron-donating (donor) and electron-withdrawing (acceptor) units as alternating groups in a conjugated oligomer or polymer that can be regulated by physical properties such as π conjugation length, monomer alteration, inter/intramolecular interactions and energy levels. Certainly, it is notable today that the highest occupied molecular orbital level of the producing material is localized predominantly on the electron-donating moiety and lowest unoccupied molecular orbital level on the electron-accepting moiety. Conjugated oligomers or polymers are used in many detecting fields due to their exceptional ability to sense toxic chemicals, metal ions and biomolecules. The conjugated polymers have unique delocalized π-electronic "molecular wires" that can expand the fluorescence intensity considerably. The fluorescence intensity of polymers can be quenched by particular quenching molecules. In this review, the fluorescence intensity, detecting of multiple metal ions, solubility, photochemical stability and optoelectronic properties of these conjugated polymers, and how they can be regulated by different functional groups, are discussed in detail.

Supramolecular Strategy Based on Conjugated Polymers for Discrimination of Virus and Pathogens.

A conjugated polymer-based supramolecular system is designed for discrimination of virus and microbes. The supramolecular system is composed of cationic polythiophene derivative (PT) and barrel-shaped macrocyclic molecular cucurbit[7]uril (CB[7]). Because PT and PT/CB[7] complexes possess different interaction manners toward virus and microbes, the rapid and simple discrimination of virus and microbes was realized through polymer fluorescence intensity change assisting with standard linear discriminant analysis (LDA). The supramolecular strategy would expand the idea of designing biological probes and further promote the extensive application of conjugated polymer materials in biosensor field.

Photophysical Properties of a Newly Synthesized Bichromophoric Polymer for Fe(III) Sensing

ABSTRACTA new kind of bichromophoric poly(acrylamide) covalently linked with norfloxacin (NF) and proflavine (PF) was synthesized. The photophysical properties of the polymer were investigated. Energy transfer from NF to PF was observed in the film state of the polymer but not effective in aqueous solution. Responses of different metal cations on the fluorescence intensity of the polymer solution were investigated. Only Fe3+ ions exhibited remarkable fluorescence intensity quenching to the polymer. The effect of Fe3+ on the solution and film of the polymer was investigated in detail. The fluorescence intensity of the bichromophoric polymer exhibited a good linear correlation with the concentration of Fe3+. © 2013 Wiley Periodicals, Inc. Adv Polym Technol 2014, 33, 21382; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21382

Plasmonic Field Effects on the Energy Transfer between Poly(p-phenyleneethynylene) Fluorescent Polymer and Au Nanocages

Colloidal gold nanocages (AuNCs) with a wall length of 60 nm and wall thickness of 6 nm were prepared by the galvanic replacement method. The AuNCs were assembled into monolayers with different percents of surface coverage, using the Langmuir–Blodgett technique. The same technique was used to coat the assembled monolayers of AuNCs with another monolayer of poly(p-phenyleneethynylene) (PPE) fluorescent polymer. The surface plasmon resonance (SPR) spectrum of the AuNCs red-shifts as the percent of AuNCs coverage increases due to growth of the interparticle surface plasmon resonance field coupling as interparticle distance decreases. While after coating the AuNCs array with PPE, the SPR of all the AuNCs monolayers arrays were red-shifted to the same position (693 nm). This unsystematic red-shift behavior is based on the presence of two plasmon fields (inside and outside of AuNCs) and is described by discrete dipole approximation (DDA) simulation. The polymer fluorescence intensity is found to decrease when the polymer is deposited over the AuNCs. This observation is due to the energy transfer between the excited PPE and the AuNCs as well interchain energy transfer. Upon turning on the plasmonic field (exciting the surface plasmon resonance band), it is found that the fluorescence intensity of the polymer increased to a maximum value at AuNCs percent coverage of 10% and then decreased as the interparticle separation distance decreased. DDA calculations showed that this is consistent with the dependence of the SPR field strength on the interparticle separation. Physically, this is a result of the interplay between the changes in the surface plasmon fields within the cavity of each nanoparticle and their external surface fields as a pair of AuNCs approach one another.

Plasmonic concentrators for enhanced light absorption in ultrathin film organic photovoltaics

We report on experimental absorption enhancement in 24 and 150-nm-thick bulk heterojunctions of the conducting polymer poly(3-hexylthiophene) and the fullerene (6,6)-phenyl C61 butyric acid methyl ester. By using periodic and quasiperiodic hole arrays as nanoengineered plasmonic concentrators milled in a silver film, a spectrally broad, omnidirectional, and polarization-insensitive absorption enhancement is observed over that of a reference layer deposited on a flat film. As the result of increased absorption, an enhancement in the polymer fluorescence intensity is also observed. This demonstrates the potential of plasmonic concentrators for improved energy harvesting in ultrathin film solar cells.

Formation of Complexes between the Conjugated Polyelectrolyte Poly{[9,9-bis(6′-N,N,N-trimethylammonium)hexyl]fluorene-phenylene} Bromide (HTMA-PFP) and Human Serum Albumin

The interaction between the conjugated polyelectrolyte poly{[9,9-bis(6'-N,N,N-trimethylammonium)hexyl]fluorene-phenylene} bromide (HTMA-PFP) and human serum albumin (HSA) has been investigated from changes observed in both the spectroscopic properties of HTMA-PFP and the intrinsic fluorescence of HSA. Absorption and fluorescence spectra of HTMA-PFP suggest that HTMA-PFP and HSA form polymer-protein complexes due to electrostatic interactions between the cationic side chains of HTMA-PFP and the negatively charged surface of the protein. Interaction between both macromolecules induces an increase in the fluorescence signal of HTMA-PFP, which suggests that hydrophobic forces also contribute to the polymer-protein complex stabilization. In addition, this interaction causes a decrease in the HSA fluorescence, partially due to static quenching and energy transfer between both macromolecules. Effects of HTMA-PFP on the thermal stability and protein conformation were explored from CD experiments. Results indicate that as polymer is added it binds to HSA and initiates unfolding. This unfolding process induces HTMA-PFP chains to become more extended, disrupting backbone interactions and increasing polymer fluorescence intensity.

Plasmonic Field Enhancement of the Exciton−Exciton Annihilation Process in a Poly(p-phenyleneethynylene) Fluorescent Polymer by Ag Nanocubes

Using the Langmuir-Blodgett (LB) technique, a poly(paraphenyleneethynylene) (PPE) fluorescent conjugated polymer was assembled on either a quartz substrate (system I) or on the surface of silver nanocube (AgNC) monolayers (system II). The fluorescence intensity of the polymer was studied in system I as a function of the surface density of the polymer sample when deposited on quartz substrates and in system II on the surface coverage of the underlying AgNC monolayers. In system I, a continual increase in the fluorescence intensity is observed as the surface density of excited polymer is increased. In system II, the fluorescence intensity of the polymer first increased until a threshold surface coverage of AgNC was reached, after which it decreased rapidly with increasing surface coverage in the AgNC monolayer. The exciting light intensity dependence is studied before and after this threshold in system II. The results suggest that one-photon processes were responsible for the increased intensity before the threshold, and two-photon processes were responsible for the rapid decrease in the polymer fluorescence intensity after the threshold. These observations are explained by the increase of the surface plasmon enhancement of the exciting light intensity as the nanoparticle surface coverage is increased. In turn, this increases the polymer absorption rate, which results in a continuous increase in the exciton density and is evident by an increase in the fluorescence intensity. At the threshold, the increased exciton density leads to an increase in the rate of exciton-exciton collisions, which leads to exciton-exciton annihilations. When this phenomenon becomes faster than the rate of fluorescence emission, an intensity decrease is observed. By exploiting the surface plasmon enhancement of absorption processes, we have observed the first exciton-exciton annihilation using a low-intensity Hg-lamp continuous wave source.

Measurement of Temperature Change in Single Hela Cells with Thermosensitive Polymers

Temperature is one of the most important parameters for living cells. Relationship between temperature and the processes in cells, i.e. effects of temperature on the cellular activities, has been studied for many years. However, there have been few studies focusing on the intracellular temperature of single living cells, because there have been few appropriate methods. In this study, we have developed a new method to measure a local temperature change inside single cells with molecular thermometers. We used thermosensitive fluorescent polymer, poly(DBD-AE-co-NNPAM-co-NIPAM) as a molecular thermometer. The fluorescence intensity of the polymer in cytosol sharply increases more than 10-fold by 6-7 °C increase around the transition temperature. We first tried to detect the thermogenesis in single HeLa cells induced by ionomycin, which was previously studied with using a micro thermometer made of a glass capillary (Suzuki, M. et al., Biophys. J. 92, L46-L48, 2007). When ionomycin was added to extracellular solution, the fluorescence intensity of polymers inside HeLa cells increased. However, the polymers also responded to DMSO, in which ionomycin was dissolved, so that this property made it difficult to accurately determine the temperature change. Therefore, we have developed another method composed of a thermosensitive sheet, which complements the measurement with polymers. As a result, we found that the temperature increase occurred due to ionomycin treatment.

Cation-sensitive fluorescence of anionic polymers bearing naphtho-18-crown-6 units

Changes in the fluorescence intensity of anionic polymers bearing naphtho-18-crown-6 moieties on addition of cations were studied in water at 30 °C. On addition of alkali metal cations, the fluorescence intensity of the polymers decreased sharply for Tl(+) less for Cs(+) and little for Li(+), K(+) and Rb(+). On addition of alkaline earth metal cations, Ba(2+) caused the strongest decrease of the fluorescence intensity of the polymers. The decrease of the fluorescence intensity of the polymers was suggested to be caused by the external heavy-atom effect of the cations bound to the cavity of the crowned naphthalene moiety. The content of the crowned naphthalene units in the polymers affected the cation-dependent fluorescence change. The fluorescence change of the polymers based on the cation complexation competition was also studied.