Controlling the optical properties of a conjugated co-polymer through variation of backbone isomerism and the introduction of carbon nanotubes

Structural and photophysical properties of PVK-F8BT copolymer thin films, with single walled carbon nanotubes: Synthesis, characterization and modeling

The nanocomposite material was elaborated (developed) by mixing of the PVK-F8BT copolymer onto the single walled carbon nanotubes SWCNTs. The new composites were prepared with various weight concentrations of SWCNTs (0.75%, 1.5% and 3%). Different experimental analyses were performed to examine their morphological features and their optical and vibrational spectroscopy behaviors as a function of the concentration of short single-walled carbon nanotubes. Π-staking interaction and the functionalization process between the copolymer and the SWCNTs have a considerable effect on the vibratory and photoemissive properties of the copolymer matrix. Scanning electron microscopy (SEM) and transmission (TEM) were used. Then, Raman scattering and steady state and time-resolved photoluminescence (PL) and (TRPL) measurements were used to study the evolution of spectroscopic characteristics and optical properties of the PVK-F8BT/SWCNTs composites. An extinction effect of PL and a decrease in the average life of the exciton time was observed. These indicated the processing of a charge transfer leading to exciton dissociations to the SWCNTs matrix. The results, also supported by DFT-based modeling method have proven a strong evidence of the functionalization and the charge transfer between the SWCNTs and the PVK-F8BT copolymer and predicted equally a correlation of structural properties.

New polymer-matrix nanocomposites based on SWCNTs and PVK-PPV copolymer: Synthesis, functionalization and characterization

An original nanocomposite material was prepared by in-situ grafting of a PVK-PPV copolymer onto SWCNTs. The new composites were elaborated with various SWCNTs weight concentrations into homemade PVK-PPV copolymer. Different experimental analyses were performed to investigate their morphological features and their optical and vibrational spectroscopy behaviors as a function of the concentration of carbon nanotubes. Π-staking and covalent interactions and functionalization process between copolymer and SWCNT undergo dramatic effect in vibrational and photoemissives properties of copolymer matrix. Transmission (TEM) and scanning electron microscopy (SEM) were used. Then, resonant Raman scattering and steady-state and time-resolved photoluminescence (PL) and (TRPL) measurements were used to study the evolution of the spectroscopic characteristics and optical properties of PVK-PPV/SWCNTs composites. As results, we have observed PL quenching effect and a decrease of average life time. These indicated the processing of a charge transfer that leads to exciton dissociations to the SWCNTs matrix. Such results, also supported by modelling based on DFT method, have given a strong evidence of the functionalization and the charge transfer between the SWCNTs and the PVK-PPV copolymer and predicted a structure-properties correlation.

Medium-mediated effects increase cell killing in a human keratinocyte cell line exposed to solar-simulated radiation

PURPOSE

The objective of this study was to investigate whether cell culture medium is a biologically relevant exposure medium that can be employed in non-ionising photobiological investigations.

METHODS

The effect of solar-simulated irradiation on cell culture medium and its ability to elicit cell death was studied. The role of reactive oxygen species (ROS), cell secreted factors, and the contribution of individual components of the medium were investigated.

RESULTS

Cell death was found to be primarily mediated through the formation of ROS via riboflavin photosensitisation and degradation in the cell culture medium. Phenol red was found to significantly reduce the cell killing ability of riboflavin. Exposures in riboflavin-free medium resulted in significantly increased cell survival compared to identical exposures in riboflavin containing medium.

CONCLUSIONS

This study has shown that solar radiation toxicity is augmented by cell culture medium due to the presence of riboflavin. Results suggest that exposures performed in phenol red-free medium may serve to increase phototoxic effects if riboflavin is present. Riboflavin-free media is recommended for solar radiation investigations to eliminate concerns regarding riboflavin photosensitisation and nutrient deprivation.

Functionalised conjugated materials as building blocks of electronic nanostructures

Two different approaches towards conjugated material (carbon nanotubes, conjugated polymers) functionalisation are presented: covalent bonding of functional groups and covalent interaction with soluble polymers. Covalent functionalisation of carbon nanotubes is made by reaction of the aromatic ring with aryl radicals, produced by reduction of diazonium ions. In the case of conducting polymers, covalent functionalisation is brought about by reaction of polyanilines with diazotized aromatic amines (including amino terminated azo dyes). The non covalent functionalisation of carbon nanotubes is made by wrapping the nanotubes with soluble conducting polyanilines. The functionalised materials are characterised by FTIR spectroscopy, X-ray diffraction, dynamic light scattering, ultraviolet-visible absorption and emission spectroscopy, transmission electron microscopy, cyclic voltammetry, differential electrochemical mass spectroscopy and conductivity measurements. The materials are to build ionic self assembled multilayers using a layer-by-layer deposition process. The charge transport and electrocatalytic behaviour of the assemblies, relevant to the application of the assemblies in nanostructured electrochemical biosensors, are evaluated using different redox molecules and/or its intrinsic electroactivity as probes.

Stereocontrolled Synthesis and Optical Properties of All-cis Poly(phenylene vinylenes) (PPVs): A Method for Direct Patterning of PPVs

Geometrically pure, all-cis poly(phenylene vinylenes) (PPVs) are synthesized by Suzuki-Miyaura-type polycondensation of 2,5-dioctyloxy-1,4-benzenediboronic acid with (Z,Z)-bis(2-bromoethenyl)benzenes, which are prepared by ruthenium-catalyzed (Z)-selective double hydrosilylation of diethynylbenzenes, followed by bromodesilylation of the resulting (Z,Z)-bis(2-silylethenyl)benzenes with N-bromosuccinimide. The all-cis PPVs thus obtained undergo one-way photoisomerization to the corresponding trans-PPVs both in solution and in the solid. This phenomenon is applied to direct microscale patterning of PPVs onto a quartz substrate.

Electrospun MEH-PPV/SBA-15 Composite Nanofibers Using a Dual Syringe Method

The process of electrospinning, which produces fibers in the nanometer to micron range under the influence of high voltages, has been widely studied to produce polymer and textile fibers. Mesoporous molecular sieve fibers have been produced in our lab, and this technique was extended to produce an interwoven mesh of polymer-molecular sieve composite fibers. The electroluminescent polymer MEH-PPV and molecular sieve SBA-15 were used to produce the composite fibers. An interesting aspect of these composites is that the fluorescence of MEH-PPV is blue shifted in the composites. The composites have been characterized by microscopy, vibrational spectroscopy, and fluorescence measurements.