Photophysical and charge transport properties of pyrazolines

Pyrazoline, an intense green emitting molecule both in solution and solid state, with extended pi-conjugation has been synthesized via simple two-step reactions in high yields. Having the electron rich pyrazoline moiety with good redox behavior, pyrazolines can be potential candidates for charge transport material in organic electronic devices. UV-Visible absorption spectra of pyrazolines exhibit peaks below 400 nm, which is a desired feature for charge transport materials because it avoids interference with donor absorption that falls in the visible to NIR region. Electrochemical and theoretical studies show that the HOMO energy level lies at around -4.8 to 5.2 eV depending on the substituents, which is in fact compatible with the PEDOT: PSS/P3HT and work function of the ITO electrode. The experimental hole transport value, measured using the hole only device and space charge limited current (SCLC) method, was found to be in the range of 10(-5) to 10(-6) cm(2) V-1 s(-1), depending on the substituents. The maximum hole mobility calculated by theoretical methods for the pyrazolines is 0.75 cm(2) V-1 s(-1)

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

Photophysical and charge transport properties of pyrazolines

Pyrazoline, an intense green emitting molecule both in solution and solid state, with extended π-conjugation has been synthesized via simple two-step reactions in high yields. Having the electron rich pyrazoline moiety with good redox behavior, pyrazolines can be potential candidates for charge transport material in organic electronic devices. UV-Visible absorption spectra of pyrazolines exhibit peaks below 400 nm, which is a desired feature for charge transport materials because it avoids interference with donor absorption that falls in the visible to NIR region. Electrochemical and theoretical studies show that the HOMO energy level lies at around −4.8 to 5.2 eV depending on the substituents, which is in fact compatible with the PEDOT:PSS/P3HT and work function of the ITO electrode. The experimental hole transport value, measured using the hole only device and space charge limited current (SCLC) method, was found to be in the range of 10<SUP>−5</SUP> to 10<SUP>−6</SUP> cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, depending on the substituents. The maximum hole mobility calculated by theoretical methods for the pyrazolines is 0.75 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>

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

Ultrasonic mediated dual-site phase transfer catalyzed polymerization of N-butenyl isatin in two phase system- a kinetic study

Use of ultrasound as an additional source for promoting polymerization reactions has gained great attention. Phase transfer catalyst (PTC) along with ultrasonication in polymerization process is an attractive methodology to achieve good yield and realizing principles of green chemistry. Herein, we reported the facile polymerization of synthesized novel N-butenyl isatin (NBI) at 60 ± 2 °C with and without ultrasonic irradiation (45 kHz; 550 W) using dual-site phase transfer catalyst (1, 4-bis (triethyl methyl ammonium) benzene dibromide, TEMABDB) and potassium peroxydisulphate (PDS or PPS) as initiator. Ultrasonication (US) promotes the formation of reactive radicals, which can be utilized effectively in phase transfer polymerization process. Hence, the rate was multi-folded (twice) in comparison with silent condition. The effect of sonication frequency and various reaction parameters on the polymerization process were investigated in both conditions. An enhancement of reaction rate under sonication was validated by activation parameter. Synthesized monomer and poly (N-butenyl isatin) was characterized by different spectral methods. Facile polymerization of N-butenyl isatin by sonication aided dual-site PTC. Green approach and mild conditions used for polymerization of NBI. Sonication lifts the rate significantly in comparison with standard condition. Effects of variables in polymerization rate were explored in both conditions. Poly (N-butenyl isatin) was analyzed by different spectral techniques.</p

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

Proton affinities of pertechnetate (TcO4-) and perrhenate (ReO4-).

The anions pertechnetate, TcO4-, and perrhenate, ReO4-, exhibit very similar chemical and physical properties. Revealing and understanding disparities between them enhances fundamental understanding of both. Electrospray ionization generated the gas-phase proton bound dimer (TcO4-)(H+)(ReO4-). Collision induced dissociation of the dimer yielded predominantly HTcO4 and ReO4-, which according to Cooks' kinetic method indicates that the proton affinity (PA) of TcO4- is greater than that of ReO4-. Density functional theory computations agree with the experimental observation, providing PA[TcO4-] = 300.1 kcal mol-1 and PA[ReO4-] = 297.2 kcal mol-1. Attempts to rationalize these relative PAs based on elementary molecular parameters such as atomic charges indicate that the entirety of bond formation and concomitant bond disruption needs to be considered to understand the energies associated with such protonation processes. Although in both the gas and solution phases, TcO4- is a stronger base than ReO4-, it is noted that the significance of even such qualitative accordance is tempered by the very different natures of the underlying phenomena