Light Emission Properties of a Cross-Conjugated Fluorene Polymer: Demonstration of Its Use in Electro-Luminescence and Lasing Devices.

Light emission properties of a fluorene cross-conjugated polymer (PF⁻1) based on the monomer 4,7-bis[2-(9,9-dimethyl)fluorenyl] benzo[1,2,5]thiadiazole are reported. This polymer exhibits solubility at high concentrations, good processability into thin solid films of good quality and a broad emission band with a fluorescence quantum yield of approximately 1. Based on these features, in this paper we implemented the use of PF⁻1 as an active layer in polymer light-emitting diodes (PLEDs) and as a laser gain medium in solution. To get insight on the conducting properties of PF⁻1, two different electron injectors, poly [(9,9-bis(3'-(N,N-dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9⁻dioctylfluorene)] (PFN) and lithium fluoride (LiF), were used in a simple PLED architecture. PLEDs with the PFN film were found to exhibit better performance with a maximum luminous efficiency of 40 cd/A, a turn-on voltage (Von) of approximately 4.5 V and a luminance maximum of 878 cd/m² at 5.5 V, with a current density of 20 A/m². For the lasing properties of PF⁻1, we found a lasing threshold of around 75 µJ and a tunability of 20 nm. These values are comparable with those of rhodamine 6G, a well-known laser dye.

Photophysical Study of Polymer-Based Solar Cells with an Organo-Boron Molecule in the Active Layer.

Our group previously reported the synthesis of four polythiophene derivatives (P1-P4) used for solar cells. The cells were prepared under room conditions by spin coating, leading to low efficiencies. However, after the addition of 6-nitro-3-(E)-3-(4-dimethylaminophenyl)allylidene)-2,3-dihydrobenzo[d]-[1,3,2] oxazaborole (M1) to their active layers, the efficiencies of the cells showed approximately a two-fold improvement. In this paper, we study this enhancement mechanism by performing ultrafast transient absorption (TA) experiments on the active layer of the different cells. Our samples consisted of thin films of a mixture of PC61BM with the polythiophenes derivatives P1-P4. We prepared two versions of each sample, one including the molecule M1 and another without it. The TA data suggests that the efficiency improvement after addition of M1 is due not only to an extended absorption spectrum towards the infrared region causing a larger population of excitons but also to the possible creation of additional channels for transport of excitons and/or electrons to the PC61BM interface.

Heparin assisted photochemical synthesis of gold nanoparticles and their performance as SERS substrates.

Reactive and pharmaceutical-grade heparins were used as biologically compatible reducing and stabilizing agents to photochemically synthesize colloidal gold nanoparticles. Aggregates and anisotropic shapes were obtained photochemically under UV black-light lamp irradiation (λ = 366 nm). Heparin-functionalized gold nanoparticles were characterized by Scanning Electron Microscopy and UV-Vis spectroscopy. The negatively charged colloids were used for the Surface Enhanced Raman Spectroscopy (SERS) analysis of differently charged analytes (dyes). Measurements of pH were taken to inspect how the acidity of the medium affects the colloid-analyte interaction. SERS spectra were taken by mixing the dyes and the colloidal solutions without further functionalization or addition of any aggregating agent.