Kinetic Spectrophotometric Determination of Propellant Grade Hydrazines using Thiophenes with Active Carbonyl Groups

A simple, cost effective, highly sensitive and rapid kinetic spectrophotometric method was developed for hydrazines by using Thiophene-3-carboxaldehyde (3-Thienaldehyde) and 3-Butenone (E)-1,1,1-trifluoro-4-(3-thienyl) (CF3 enone). CF3 enone was prepared by crossed aldol condensation of 3-Thienaldehyde and characterized by UV-Vis, FT-IR and NMR spectra. Reactions of 3-Thienaldehyde (with catalyst) and CF3 enone (in acetonitrile medium without catalyst) with hydrazines were followed spectrophotometrically and compared. Variables such as temperature and concentration were optimized to determine hydrazines in the concentration range of 0.1 mM to 0.1 M for 3-Thienaldehyde and 0.1 mM to 1 mM for CF3 enone. Minimum detectable limits were found to be 0.2 mM (Hydrazine) and 0.1 mM (MMH ) for 3-Thienaldehyde. For CF3 enone, Minimum detectable limits were found to be 0.007 mM (Hydrazine) and 0.01 mM (MMH). Rate of the CF3 enone reaction was studied as there is gradual decrease in absorbance for the peak at 320 nm for the interaction of hydrazines. Initial rate and fixed time methods were adopted for kinetic study. CF3 enone based kinetic spectrophotometric method is rapid and sensitive with no catalyst requirement for interaction of hydrazines when compared with the classical CHO functional group based method.Defence Science Journal, Vol. 64, No. 1, January 2014, DOI:10.14429/dsj.64.309

Nanoscale Functionalization of Surfaces by Graft-Through Sonogashira Polymerization

Graft through Sonogashira polymerization was used to functionalize various surfaces with conjugate polymers in a dimension of less than 100 nm. Atomic force microscopy measurement revealed a dense surface coverage with several closely packed islands. UV-vis spectroscopy and cyclic voltametry measurements suggested a moderate band gap, which is important for various applications in material science. A device was fabricated using polymer functionalized ITO and deposited aluminium as cathode to determine the current-voltage (I-V) characteristics and charge carrier mobility. Space charge limited current method indicated moderate charge carrier mobility while I-V characteristic data indicated its behaviour as semiconducting material

Self-assembly of a white-light emitting polymer with aggregation induced emission enhancement using simplified derivatives of tetraphenylethylene

White-light emitting materials and devices have gained a great deal of interest and play an important role in next generation solid-state lighting applications. The unique aggregation-induced emission (AIE) route offers a forthright solution to the bottleneck problem of aggregation caused quenching (ACQ) in the solid state. A significant fluorescence enhancement was realized by tailoring a new luminogen (2Z,2′Z)-3,3′-((9,9-dihexyl-9H-fluorene-2,7-diyl)bis(3,1-phenylene))bis(2-(4-bromophenyl)-3-phenylacrylonitrile) (FBPAN) based on the AIE strategy, which exhibits yellow fluorescence with a high quantum yield of 63.41%. Electroluminescence characteristics with a maximum luminance, current and power efficiency of 16673 cd m−2, 9.32 cd A−1 and 5.88 lm W−1, respectively, were obtained for FBPAN. The white light emitting polymers were obtained by the copolymerization of a 9,9′-dihexylfluorene host with a FBPAN moiety as a covalent dopant. Bright white light emission with a high quantum yield of 80.2% was obtained from the copolymer FBPAN 0.5, which contained 0.5% FBPAN. Importantly, the copolymers exhibit enhanced emission upon aggregation, even at low compositions of FBPAN. A careful inspection reveals that the enhanced emission in the solid state is due to the formation of “J-aggregates” with ordered supramolecular self-assembly. Interestingly, the copolymer FBPAN 0.5 exhibits a unique ordered flower shaped self-assembly and significantly reduces the charge trapping due to balanced charge transport. As a result, bright and high efficiency white light emission was achieved with Commission Internationale de l'Eclairage (CIE) coordinates of (0.32, 0.31) and a maximum luminance, current and power efficiency of 13455 cd m−2, 7.56 cd A−1 and 5.32 lm W−1, respectively. The copolymers possess very low turn-on voltage in the range of 1.5 to 3 V

White light emitting single polymer from aggregation enhanced emission: a strategy through supramolecular assembly

Aggregation induced emission enhancement (AIEE) is widely regarded as an efficient tool to offset the problem of aggregation caused quenching (ACQ) in luminogens. The ACQ phenomenon in small organic molecules and polymers is detrimental to the performance of OLEDs. Efficient pure white electroluminescent polymers, obtained by the copolymerization of 9,9-dihexylfluorene as a blue host with (E)-2,7-dibromo-9H-fluoren-9-yl-2-cyano-3-(4-(dimethylamino)phenyl) acrylate (FCP) as a yellow emitting covalent dopant with AIEE properties on the main chain of the copolymers, have been designed and synthesized. White light emission was achieved in copolymer FCP 2.5, which contained 2.5% of the AIEE luminogen. Interestingly the copolymers exhibited an enhanced emission upon aggregation even at low compositions of FCP. The enhanced emission in the copolymers is attributed to the supramolecular assembly of the polymeric chains. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) investigations of the monomer and copolymers of FCP revealed the presence of an intramolecular charge transfer (ICT) transition between dimethylamine and the cyanoacrylic acid unit. OLEDs were fabricated using a device with a ITO/PEDOT:PSS/EML/Al structure. White light emitting diodes were fabricated from FCP 2.5 as the emissive layer (EML) and elicited a white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinate values of (0.33, 0.34). They exhibited a maximum brightness of nearly 9332 cd m−2, a power efficiency of 4.13 lm W−1 and a luminous efficiency of 6.34 cd A−1. Interestingly, the supramolecular ordering in FCP 2.5 considerably reduces the charge trapping which results in a reproducible white light emission

Studies on Föster resonance energy transfer in blends of thienylene vinylenes for white light emitting diodes

Conjugated polymer blends are widely used for realization of white light emitting diodes (WPLEDs). The theoretical understanding of the transfer of energy from high band gap host to the low band gap dopant is very important for designing an efficient and stable white LED system. Novel geometric isomers of thienylene vinylene are studied here for resonant energy transfer between the components of the blends. In this study we report a novel methodology for a simple and pictorial depiction of resonant energy transfer between conjugated polymers in blend for a quick screening of prospective constituents prior to synthesis of these polymeric materials. The resonant energy transfer is also supported by the experimental observations which show a spectral overlap. The sequence of energy transfer predicted by theory is in agreement with the order of band gap of the constituent polymers. The resulting fluorescence spectrum of the blends gave a broad emission in the visible region and is of great significance in the development of white light emission

Offsetting the problem of charge trapping in white polymer light-emitting diodes using a fluorenone-based luminogen

In this study, we propose a strategy to offset charge trapping and to enhance the confinement of excitons in the emissive layer of white electroluminescent copolymer using a luminogen with aggregation-induced emission enhancement (AIEE). The fluorenone-based luminogen, 2,7-bis(9H-fluoren-9-one-2yl)-9,9-dihexylfluorene (FF) that exhibited yellow emission with AIEE property is copolymerized with 9,9-dihexylfluorene in different compositions to tune the emission color. White-light emission is demonstrated in a copolymer FF-0.25, which contained 0.25% of FF in the polymer backbone. Interestingly, the copolymers exhibited enhanced emission upon aggregation in thin film, even in low FF composition. OLEDs fabricated from the copolymer FF-0.25 elicited a white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of 0.30, 0.31 with a power efficiency of 4.12 lm W<SUP>−1</SUP>. FF-0.25 showed very low charge trapping compared to other white emitting single polymer OLEDs reported to date. The reduced charge carrier trapping is attributed to the positioning of energy levels in the copolymer that resulted in almost equal electron- and hole-injection barriers. A theoretical investigation on the copolymers of FF revealed the presence of an ambipolar property and low exciton binding energy implicit of efficient formation and confinement of excitons within the emissive layer. The system represents the first ambipolar white electroluminescent polymer designed by using an AIEE luminogen

A solution processable fluorene–fluorenone oligomer with aggregation induced emission enhancement

Herein, we report a novel solution processable fluorenone based small molecule with an Aggregation Induced Emission Enhancement (AIEE) property. In contrast to previous reports, the presence of the fluorenone moiety in FF triggers the AIEE property