An unconventional route to an ambipolar azaheterocycle and its in situ generated radical anion.

Herein we report the synthesis, characterization and application of an azaheterocycle 4 obtained via an unprecedented C-N coupling. The neutral azaheterocycle undergoes one-electron reduction to form an air-stable radical anion in situ, which provides added benefit towards operational stability of the device during n-type charge transport. The unusual stability of this radical anion is due to the fact that the fused cyclopentane ring upon reduction forms aromatic cyclopentadienyl anion, and the negative charge delocalizes over the nearly planar azaheterocycle core. The present azaheterocycle can be considered as a mimic of a fullerene fragment, which shows balanced ambipolar charge transport in space charge limited current (SCLC) devices with moderate hole (µh) and electron (µe) mobilities (µh = 2.96 × 10-3 cm2 V-1 s-1 and µe = 1.11 × 10-4 cm2 V-1 s-1). Theoretical studies such as nucleus independent chemical shifts (NICS) calculations, anisotropy of the induced current density (ACID) plots, spin density mapping and anisotropic mobility calculations were performed to corroborate the experimental findings.

Remarkably Efficient Blood-Brain Barrier Crossing Polyfluorene-Chitosan Nanoparticle Selectively Tweaks Amyloid Oligomer in Cerebrospinal Fluid and Aß1-40.

Amyloid oligomers have emerged as a key neurotoxin in Alzheimer's dementia. Amyloid aggregation inhibitors and modulators have therefore offered potential applications in therapeutics and diagnosis. However, crossing the blood-brain barrier (BBB) and finding the toxic aggregates among aggregates of different sizes and shapes remain a challenge. The ability of identifying early aggregates can provide a new approach to find inhibitors of the initial nucleation events correlating presenile dementia. In this study, we have prepared polyfluorene nanoparticles using chitosan as an additive, which enables it to cross BBB efficiently and employed as a highly efficient amyloid oligomer modulator. The polymer conjugate, polyfluorene-chitosan (PC), shows no toxicity in MTT assay and precludes self-aggregation of Aß1-40 and human cerebrospinal fluid oligomers to final fibril formation. This modulation strategy is supported by thioflavin T assay, circular dichroism studies, atomic force microscope images, and Fourier transform infrared analysis. The polymer-protein interface exhibits the presence of co-aggregates and responded with a stable optical response. The simple synthesis to get desired sizes and shapes with necessary photophysical behavior, biocompatibility, and most prominently BBB permeability makes this polymer conjugate very unique and highly attractive for modulation of amyloid oligomers selectively as well as for developing next generation nanotheranostic materials toward presenile dementia.

Receptor-Free Detection of Picric Acid: A New Structural Approach for Designing Aggregation-Induced Emission Probes.

A pristine aggregation-induced enhanced emission (AIEE) active monomer 2,5-bis(( E)-4-bromostyryl)-3,4-diphenylthiophene (TPBZ) and its copolymer (PFTPBZ) with 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propandiol) ester have been synthesized via Suzuki coupling polymerization. PFTPBZ that is devoid of any receptor showed AIEE property and demonstrated excellent and selective fluorometric recognition of 2,4,6-trinitrotoluene (TNT) in aggregated state (aqueous medium) and picric acid (PA) in aggregated state and solution state (organic solvent) as well as in vapor phase via PFTPBZ dip-coated Whatman filter paper on a solid-phase platform in 1.86 ng level (naked eye). Limit of detection (LOD) for TNT in 95% water fraction ( fw) was 53.74 × 10-6 M, and at 40% fw, it was 14.26 × 10-7 M. PA detection in tetrahydrofuran solution was possible with a LOD of 28.16 × 10-7 M, 95% fw with LOD of 10.47 × 10-6 M, and in 40% fw with LOD of 47.39 × 10-8 M. As a unique example of structural design, the probe PFTPBZ surprisingly possesses no receptor, yet remarkably high selectivity was achieved via Förster resonance energy transfer (FRET) and photoinduced electron transfer from the copolymer PFTPBZ to PA and TNT. Detection of PA in the presence of various metal analytes and inorganic acids in real water samples (lakes, rivers, and sea water) was also demonstrated using this concept of receptor-free conjugated polymer probe.

Effect of fluorine substitution and position on phenylene spacer in carbazole based organic sensitizers for dye sensitized solar cells.

The preparation of a series of organic dyes having a carbazole donor, cyanoacrylic acid as an acceptor, and phenylene ring as a spacer with the difference in the positions of fluorine substitution is reported. Due to its unique properties of small size and high electronegativity, fluorine is now being extensively used to control the optoelectronic properties of organic conjugated materials. In this study, the results revealed that the specific position and number of fluorine substitution were very crucial to control the optical as well as the electrochemical properties of organic dyes. It was found that fluorine substitution led to a redshift in the absorption spectra of the dyes and reduced the band gap. The injection rate of photoexcited electrons was measured using time-resolved photoluminescence and the o-fluoro substituted dye MA1F-o showed the best electron injection dynamics. As a result of broad absorption and high electron injection rate, the dye MA1F-o outperformed other dyes with a power conversion efficiency of 4.02% (Jsc = 8.3 mA cm-2, Voc = 0.75 V and FF = 0.64). The non-fluorinated dye MA0F exhibited a power conversion efficiency of 3.23% (Jsc = 6.8, Voc = 0.72 and FF = 0.67). The dye MA1F-m exhibited the least molar absorption coefficient and a lower power conversion efficiency because of the meta inductive effect.

High-performance n-channel organic thin-film transistor based on naphthalene diimide.

A conjugated molecule comprising 1,4,5,8-naphthalene diimide (NDI) substituted with two octadecylamine (OD) chains has been synthesized (NDI-OD2) in a single step from commercial materials, and its organic thin-film transistor (OTFT) devices on glass substrate have been studied using poly(vinyl alcohol) (PVA) gate dielectric material. Although we utilized the PVA dielectric without any intermediate buffer layer or PVA cross-linkers, excellent electron mobility as high as ∼1.0 cm(2)V(-1) s(-1) are obtained. This NDI-OD2 molecule exhibits comparable optical (Eg(UV) ∼3.1 eV) and electrochemical band gaps (Eg(CV) ∼3.02 eV) with a lowest unoccupied molecular orbital (LUMO) energy levels of ∼3.3 eV. When processed by solution method, this material forms rod-shaped crystalline microstructures, whereas, when thermally deposited, it assumes the formation of smooth 2D films. The chemical as well as physical properties and theoretical calculations of NDI-OD2 have been studied and the effect of the C-18 alkyl chain unit has been discussed. The OTFT consisting of NDI-OD2 exhibits excellent performance parameters such as high electron mobility (µe) and Ion-to-Ioff ratio. After demonstrating the high performance of NDI-OD2-based TFT devices fabricated with biocompatible PVA dielectric, we have also demonstrated that these devices can be degraded because of the presence of this PVA dielectric when exposed to a high-moisture environment. The systematic degradation of the device activity in a controlled way within 10 days of exposure (>80% moisture) is also presented here. In this study, a conceptually important feature and futuristic aspect that the n-channel TFT devices can also be biodegraded irreversibly is demonstrated. This concept of developing a low cost and biodegradable OTFT device with biocompatible PVA dielectric with excellent electron mobility is expected to have diverse applications in disposable electronic tags, biomedical devices, and food industry packing.