Search results for "Conjugated system"
showing 10 items of 225 documents
Carbon nitride as photocatalyst in organic selective transformations
2020
Abstract Graphitic carbon nitride (g-C3N4) is a metal-free conjugated polymer which has become a new research hotspot in photocatalysis. It can be used for solar energy exploitation like in solar energy organic synthesis, one of the most new and appealing green applications of heterogeneous photocatalysis. This chapter resumes the state-of-the-art and progresses in the application of heterogeneous visible light photocatalysis in organic selective transformations by using C3N4 as photocatalyst.
Excitons and nonlinear optical spectra in conjugated polymers.
1992
Excitons in conjugated polymers are studied theoretically in the Su-Schrieffer-Heeger model supplemented by long-range Coulomb interactions. The relationship between exciton energies and basic interaction parameters is clarified. Linear and third-order nonlinear optical susceptibilities (two-photon absorption, electroabsorption, and third-harmonic generation) have been calculated, elucidating the significance of singlet and triplet excitons and unbound electron-hole pairs. Using only moderate interaction strength, various experiments in polydiacetylene can be interpreted in a consistent way
Living Light-Induced Crystallization-Driven Self-Assembly for Rapid Preparation of Semiconducting Nanofibers.
2018
Well-defined nanostructures composed of conjugated polymers have attracted significant attention due to their intriguing electronic and optical properties. However, precise control of the size and uniformity of these semiconducting nanostructures is still rare and challenging, despite recent advances in strategies to obtain self-assembled nanostructures with narrow dispersions. Herein, we demonstrate the preparation of fluorescent conjugated block copolymers by one-shot polymerization and rapid formation of nanofibers in a few minutes via light-induced crystallization-driven self-assembly, driven by facile cis-to- trans photoisomerization of its poly( p-phenylenevinylene) blocks. Furthermor…
Photoluminescence ZnO nanorod biosensors for medical and food safety applications
2017
Photoluminescence (PL) ZnO nanorods (NR) are prospect materials for biosensor applications. They can be deposited on solid state substrates and/or dispersed in liquid media. ZnO NRs demonstrate strong UV emission (3.28–3.3 eV), which depends on surface charge, formed by adsorbed molecules. In the present work we report on ZnO NRs, deposited on glass slides, used as biosensor templates for detection food pathogens. Change of ZnO PL after interaction with biomolecules was recorded. Dependence of PL intensity vs concentration of biomolecules was obtained. In the second part, ZnO nanorods were used as PL biomarkers. A suspension of ZnO NRs, conjugated with SSEA-4 antibodies (aSSEA-4) in PBS buf…
Tetra-alkoxy substituted PPV derivatives: a new class of highly soluble liquid crystalline conjugated polymers
2011
Two first examples of highly soluble tetra-alkoxy substituted PPV derivatives, poly(2,3,5,6-tetrahexyloxy-1,4-phenylene vinylene) (TH-PPV) and poly[2,3,5,6-tetra(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] TEH-PPV, are presented. Both polymers have been fully characterized and the solubility and UV-Vis absorption characteristics have been studied in various organic solvents. Due to the symmetric nature of the repeating unit, TH-PPV and TEH-PPV have an inherently regioregular nature, which is unusual for PPV-type polymers. Observations from polarized light microscopy and differential scanning calorimetry indicate that TH-PPV exhibits thermally induced order resulting in a liquid crystalline m…
Synthesis and characterisation of novel chemical conjugates based on alpha, beta-polyaspartylhydrazide and beta-cyclodextrins
2006
A new family of supramolecular systems based on a synthetic polyaminoacid and cyclic oligosaccharides such as beta-cyclodextrins (beta-CDs) was synthesised. The pharmaceutical potential of these systems arises from the proper combination between the complexing properties of cyclodextrins and the particular pharmacokinetic profile that can be obtained by using macromolecular conjugates with a biocompatible backbone. Five supramolecular conjugates were synthesised by using alpha,beta-polyaspartylhydrazide (PAHy) as a polymeric component and various amounts of two P-CD derivatives. In particular, by reaction of PAHy with beta-CD monoaldehyde, samples named as A(1), A(2) and A(3), bearing, resp…
Topology-Dependent Swichability of Peptide Secondary Structures in Bioconjugates with Complex Architectures
2013
Peptide sequences, which exhibit a reversible pH-responsive coil to α-helix secondary structure transition, are conjugated to polymer precursors to yield linear AB and graft ABA peptide-poly(ethylene oxide) conjugates. While the PEO B-block is comparable, the conjugates differ in topologies of the peptide bearing A-blocks. The influences of topology on the structure transitions in the peptide segments are investigated, comparing linear AB-bioconjugates with graft ABA-bioconjugates having multiple peptide segments combined in star or pom-pom topologies.
Hairy Aramide Rod−Coil Copolymers
2010
We have synthesized monodisperse “hairy rod oligomers” based on oligo(p-benzamide)s carrying alkyl side chains and conjugated them with polydisperse poly(ethylene glycol) (PEG) chains. The well-defined oligomers were synthesized from 4-amino-2-hexyloxybenzoic acid using a commercial peptide synthesizer. The PEG conjugated hairy rod−coil block copolymers self-assemble in polar and nonpolar organic solvents. The self-organization in solution was investigated by dynamic light scattering (DSL) and transmission electron microscopy (TEM) as a function of solvent, equilibration time, and polarity of the substrate. Individual fibers and fiberlike bundles of aggregates could be observed. As all hydr…
Synthesis and characterization of poly(phenylacetylenes) featuring activated ester side groups
2010
Four monomers based on 4-ethynylbenzoic acid have been synthesized, one of those featuring an activated ester. With the metathesis catalytic system WCI 6 /Ph 4 Sn, these acetylenic monomers could successfully be polymerized yielding conjugated polymers with molecular weights of around 10,000 to 15,000 g/mol and molecular weight distributions M w / M n < 2.1. Also the copolymerization of phenylacetylene or methyl 4-ethynylbenzoate with pentafluorophenyl 4-ethynyl-benzoate as reactive unit was conducted. Polymer analogous reactions of the reactive polymers and copolymers with amines have been investigated and it was found that poly(pentafluorophenyl 4-ethynylbenzoate) featured a significant r…
1997
On the basis of an extended series of monodisperse oligomers of the dialkoxy-substituted phenyleneethenylenes 1a–i the Eqs. (3) and (4) were conceived in order to determine the limiting values of the energies Ei and the wavelengths λi of the UV/vis absorption. The convergence of the Ei, and λi values with a growing number n of repeating units permits a precise prediction of the Ei,∞ and λi,∞ values of the corresponding polymer 1j as well as a statement about the overall effect of conjugation ΔEi and the effective conjugation length ECL. A great variety of different conjugated oligomers 2–14 can be evaluated by the same algorithm.