Helicene Aromaticity Deviates from the Clar Rule-On the Electronic Dissimilarity of Large Isomeric Fibonacenes.

This combined experimental and theoretical study illustrates the profound consequences of non-planarity on the electronic properties of polycyclic arenes. Three isomeric [10]fibonacene tetraesters were synthesized through a robust and regiocontrolled Perkin/Mallory approach: a nearly planar [10]phenacene derivative, a moderately twisted [10]semicircle derivative, and a 3D non-planar [10]helicene derivative. The photophysical properties of the 3D [10]helicene isomer were found to be dramatically different from the comparable ones of the [10]phenacene and [10]semicircle isomers. The aromatic properties of the [10]phenacene and [10]semicircle isomers conform well with their predictive Kekulé and Clar analyses, but the [10]helicene isomer deviates from these general topological rules, which appears to be a general phenomenon for [n]fibonacenes with n≥9.

Charge carrier transport in perylene-based and pyrene-based columnar liquid crystals.

Electron and hole transport characteristics were evaluated for perylene-based and pyrene-based compounds using electron-only and hole-only devices. The perylene presented a columnar hexagonal liquid crystal phase at room temperature with strong molecular π-stacking inside the columns. The pyrene crystallizes bellow 166 °C, preserving the close-packed columnar rectangular structure of the mesophase. Photophysical analysis and numerical calculations assisted the interpretation of positive and negative charge carrier mobilities obtained from fitting the space charge limited regime of current vs voltage curves. The pyrene-based material demonstrated an electron mobility two orders of magnitude higher than the perylene one, indicating the potential of this class of materials as electron transporting layer.

Shedding Light on Highly Emissive 1,4-Dihydropyrrolo[3,2-b]pyrrole Derivatives: Synthesis and Aggregate-Dependent Emission.

Three tetraaryl-1,4-dihydropyrrolo[3,2-b]pyrrole derivatives containing different number of long alkoxy chains (2, 4 and 6) were synthesized, characterized and applied in Organic Light Emitting Diodes (OLEDs). The compounds showed good emission properties with Photoluminescence Quantum Yields (PLQYs) higher than 80 % in solution and 50 % in solid state (thin film). The solvatochromism results revealed a pronounced vibronic emission in methylcyclohexane and toluene, characterized by two distinct sharp emission peaks and a small redshift in the following order: methylcyclohexane>toluene>dichloromethane>tetrahydrofuran>acetonitrile. Also, the compounds formed aggregates with redshifted emission, which can be attributed to excimer formation. This phenomenon was observed in solutions containing 90 % water and with the concentration variation in methylcyclohexane (MCH). Compounds with a greater number of peripheral chains showed the capacity to keep hexagonal columnar organization in films after fast cooling from liquid state. OLEDs fabricated with these compounds showed turn-on voltages lower than 4.0 V, with luminance higher than 1400 cd m-2 , electroluminescence spectra with Full Width at Half Maximum lower than 70 nm and maximum External Quantum Efficiency between 7.2 % and 4.3 %. Overall, this shows that the 1,4-dihydropyrrolo[3,2-b]pyrrole moiety is promising for applications where luminescence is paramount, as in organic light-emitting devices.

Dissymmetric Triaryltriazines: Small Mass Columnar Glasses.

Columnar liquid crystals with very small molecular masses that form anisotropic glasses well above room temperature are obtained by mixed dissymmetric substitution of sym-triazine with ester-bearing phenyl and phenanthryl or tetrahelicenyl moieties. The combination of low molecular symmetry with configurational flexibility and short polar ester moieties stabilizes the mesophase over large temperature ranges and induces pronounced calorimetric glass transitions within the anisotropic fluid despite the smallness of the molecules. In contrast to more symmetrical homologs, no ester tails longer than ethyl are necessary to induce the liquid crystalline state, allowing for the near-absence of any insulating and weight-increasing alkyl periphery. Films drop-cast from solution show in all cases emission spectra that do not show significant change of fluorescence emission upon annealing, indicating that the columnar hexagonal mesoscopic order is obtained directly upon deposition from solution and is resistant to crystallization upon annealing.

Columnar Liquid Crystalline Glasses by Combining Configurational Flexibility with Moderate Deviation from Planarity: Extended Triaryltriazines.

Triply phenanthryl- and tetrahelicenyl-substituted triazine-hexaalkyl esters with short alkyl chains show glass transitions conveniently above room temperature within the hexagonal columnar liquid crystalline state, resulting in a solid columnar order at room temperature. As the hexagonal columnar mesophase is easily aligned with the director perpendicular to a solid substrate, such glassy columnar liquid matrices are aimed at for the orientation of guest emitters, to obtain anisotropic emission. A condition for face-on alignment on substrates are attainable melting and clearing temperatures, which is achieved with the moderately nonplanar tetrahelicenyl derivatives in spite of their short alkyl periphery. An unusual phase transition between two columnar mesophases of same hexagonal symmetry, but very different long-distance regularity of the column lattice, is found in one phenanthryl homolog.

Room Temperature Phosphorescence in Solution from Thiophene-Bridged Triply Donor-Substituted Tristriazolotriazines.

Most organic room-temperature phosphorescence (RTP) emitters do not show their RTP in solution. Here, we incorporated sulfur-containing thiophene bridges between the donor and acceptor moieties in D3 A-type tristriazolotriazines (TTTs). The thiophene inclusion increased the spin-orbit coupling associated with the radiative T1 →S0 pathway, allowing RTP to be observed in solution for all compounds, likely assisted by protection of the emissive TTT-thiophene core from the environment by the bulky peripheral donors.

The effect of substituents and molecular aggregation on the room temperature phosphorescence of a twisted π-system.

Considering the relevance of room temperature phosphorescent (RTP) materials, we discuss the influence of donor and acceptor groups substituted on to a twisted three-fold symmetric hydrocarbon homotruxene, which presents a persistent RTP, even in the absence of donor or acceptor moieties, under ambient conditions as a result of the twisted π-system. Compared to a fluorine acceptor, a donor methoxy group increases the phosphorescence decay rate in solution, while in the solid-state, molecular aggregation and packing yield a very persistent phosphorescence visible by the eye. The RTP of the intrinsically apolar homotruxene is found to be modulated by polar substituents, whose main impact on the solid-state emission is due to altered packing in the crystal.

Enhancing the phosphorescence decay pathway of Cu(I) emitters - the role of copper-iodide moiety.

Speeding up the phosphorescence channel in luminescent copper(I) complexes has been extremely challenging due to the copper atoms relatively low spin-orbit coupling constant compared to heavier metals such as iridium. Here, we report the synthesis and characterization of three mononuclear copper(I) complexes with diimines, triphenylphosphine, and iodide ligands to evaluate the effect of the copper-iodide (Cu-I) moiety into the phosphorescence decay pathway. Temperature-dependent photophysical studies revealed combined thermally activated delayed fluorescence and phosphorescence emission, with a phosphorescence decay rate of the order of 104 s-1. Density functional theory calculations indicate very high spin-orbit coupling matrix elements between the low-lying states of these complexes. Compared to the classical [Cu(phen)(POP)]+, our results demonstrate that Cu-I is a versatile moiety to speed up the phosphorescence decay pathway in about one order of magnitude, and it can be prepared by a simplified synthetic route with few synthetic steps. Furthermore, the SOC matrix elements and the phosphorescence decay rates of these complexes are comparable to those of extensively applied coordination complexes based on heavier metals, making them a promising alternative as active layers of organic light-emitting diodes.

Halogenation of a twisted non-polar π-system as a tool to modulate phosphorescence at room temperature.

Halogenation of a twisted three-fold symmetric hydrocarbon with F, Cl or Br leads to strong modulation of triplet-triplet annihilation and dual phosphorescence, one thermally activated and the other very persistent and visible by eye, with different relative contributions depending on the halide. The room temperature phosphorescence is highly unusual given the absence of lone-pair-contributing heteroatoms. The interplay between the spin-orbit coupling matrix elements and the spatial configuration of the triplet state induces efficient intersystem crossing and thus room temperature phosphorescence even without relying on heteroatomic electron lone pairs. A ninefold increase of the ISC rate after introduction of three bromine atoms is accompanied by a much higher 34-fold increase of phosphorescence rate.

Highly emissive MAPbBr3perovskite QDs by ligand-assisted reprecipitation: the antisolvent effect.

A systematic study of the synthetic procedure to improve quantum efficiency of luminescent hybrid perovskite QDs through ligand-assisted precipitation method is presented. Particularly, the influence of the dielectric constant and dipole moment of the antisolvent on the reaction time and the photophysical properties of the QDs is highlighted. After evaluating the influence of antisolvents and optimizing experimental parameters such as reaction time and Pb excess of the precursor, colloidal crystalline MAPbBr3QDs with exceptionally high absolute quantum yield up to 97.7% in solution and 69.1% in solid film were obtained. Finally, MAPbBr3QDs precipitated from anisole were processed like UV-curable nanocomposite as efficient down conversion layer resulting in very narrow green emission light-emitting diode.

Electrochemical impedance biosensor for detection of saxitoxin in aqueous solution.

Saxitoxin is a cyanotoxin which is very harmful to human health; the concentration limit in drinking water is only 3 µg/L. Therefore, a simple, fast, sensitive, low-cost, and specific method for its detection, quantification, and monitoring in water bodies is needed to avoid adverse effects on animal and human health. In this work, we developed an electrochemical impedimetric biosensor using a specific aptamer as recognition element for saxitoxin detection. This method allies the superior sensing characteristics of aptamers with the nondestructive, label-free, and easy working principles of the electrochemical impedance technique. The device presented sensitivity for detecting saxitoxin concentrations above 0.3 µg/L, with high selectivity in negative control experiments, demonstrating a promising alternative for water toxin detection.

Nematic Triphenyltriazine Triesters and the Induction of the Columnar Mesophase by Fluorine Substitution.

Whereas their para homologs are not mesogenic, the disk-shaped triphenyltriazine meta-trialkylesters obtained via trimerization of 3-cyanobenzoic alkylester, which are configurationally more flexible, exhibit a monotropic nematic mesophase. Introduction of fluorine atoms into the alkyl chains or into the phenyl moieties leads to the appearance of an enantiotropic columnar mesophase. If fluorine is introduced both in the chains and in the phenyl moieties, only a monotropic mesophase remains. Fluorination of either the alkyl chains or the aromatic core, but not both, appears thus as a simple means of inducing or stabilizing columnar self-assembly in disk-shaped systems. As the homeotropically alignable columnar mesophase can thus be made to persist at room temperature, as energies higher than 3 eV of the first excited triplet state are computed in agreement with the value reported for the parent arene, and as they are not fluorescent themselves, these compounds are of promise as aligning host matrices for blue-emitting TADF devices with improved light outcoupling. Dilution of a columnar with a nonmesogenic homolog induces the nematic state, indicating that the nanoscopic make-up of both mesophases is closely related.

Insight into Out-of-Layer Fluctuations in the Smectic A Stability of 3,5-Diarylisoxazole Liquid Crystals.

Polar-terminated 3,5-diarylisoxazole liquid crystals (ILCs) were synthetized and characterized. ILCs are composed by rigid core 3,5-diarylisoxazol, alkyl chain and polar-terminated flexible spacer. Hydroxyl-, ketal- and 1,2-diol-terminated ILCs rendered smectic C and A mesophase, while bromine-terminated ILCs showed smectic A and B mesophase, for monosubstituted and linear ILCs. For branched alkyl chain monotropic SmA was detected and for disubstituted ILCs no mesophase was detected. Out-of-layer fluctuations (OLFs) are discussed based on X-ray diffraction date and textures. The OLFs are dependent on the bromine atom hardness, hydrogen bonding through collective actions and conformational effects at the interface between layers. Smectic translational order parameter (TOP) Σ was also obtained for orientated bromine- and hydroxyl-terminated ILCs and related it with OLFs. For 1,2-diol-terminated ILCs two SmC sublayers were founded, probably related to the intramolecular hydrogen bond favoring the 5-membered and 6-membered formation.

Persistent Solid-State Phosphorescence and Delayed Fluorescence at Room Temperature by a Twisted Hydrocarbon.

The dehydrating cyclotrimerization of 1-tetralone in the presence of titanium tetrachloride at high temperatures leads to homotruxene, a nonplanar arene in which the twist angles between its three outer benzene rings and the central benzene are stabilized by ethylene bridges. This non-planar configuration allows for pronounced spin-orbit coupling and a high triplet energy, leading to room-temperature phosphorescence in air with a lifetime of 0.38 s and a quantum yield of 5.6 %, clearly visible to the human eye after switching off the excitation. Triplet-triplet annihilation is found to simultaneously lead to a substantial delayed fluorescence, unprecedented from a pure hydrocarbon at ambient conditions, with a lifetime of 0.11 s.

Lateral Flow Assay for Interleukin 6: A Technological and Scientific Prospection of a 10-Year Survey.

BACKGROUND: Interleukin-6 (IL-6) is a multifunctional cytokine that plays a crucial role not only in the immune system but also in numerous biological processes. Elevated IL-6 levels have been observed in many types of cancer and inflammatory diseases. Among the techniques that have been used to quantify IL-6, a Lateral Flow Assay (LFA) is one of the most promising. OBJECTIVE: The objective of this study was to perform a technological and scientific exploration of the development of an LFA for IL-6. METHOD: The Instituto Nacional de Propriedade Industrial-INPI (Brazil), European Patent Office - Espacenet, and United States Patent and Trademark Office-USPTO were used for the technological prospection to consider all the patents regarding an LFA for IL-6 detection. For the scientific investigation, the following periodic databases were used: Web of Science, Science Direct, PubMed, and Scielo, and were monitored from 2007 to May 2017. RESULTS: We found no patents based on the searched keywords, and a limited number of scientific articles were found. Therefore, the development of an LFA sensor for the detection of IL-6 appears to be innovative with significant biotechnological importance, creating a technology transfer to promote economic and industrial growth. CONCLUSION: The development of lateral flow immunosensors for IL-6 is innovative, as we could not find patents describing such a biosensor. Scientific prospection reported two lateral flow immunosensors. However, the test for IL-6 cannot be completed without using some kind of equipment for detection, such as the one we propose in future developments.

High rectification in organic diodes based on liquid crystalline phthalocyanines.

The optical and electrical properties of mesogenic metal-free and metalated phthalocyanines (PCs) with a moderately sized and regioregular alkyl periphery were investigated. In solution, the individualized molecules show fluorescence lifetimes of 4-6 ns in THF. When deposited as solid thin films the materials exhibit significantly shorter fluorescence lifetimes with bi-exponential decay (1.4-1.8 ns; 0.2-0.4 ns) that testify to the formation of aggregates viaπ-π intermolecular interactions. In diode structures, their pronounced columnar order outbalances the unfavorable planar alignment and leads to excellent rectification behavior. Field-dependent charge carrier mobilities are obtained from the J-V curves in the trap-limited space-charge-limited current regime and demonstrate that the metalated PCs display an improved electrical response with respect to the metal-free homologue. The excited-state lifetime characterization suggest that the π-π intermolecular interactions are stronger for the metal-free PC, confirming that the metallic centre plays an important role in the charge transport inside these materials.

Thermal Evaporation versus Spin-Coating: Electrical Performance in Columnar Liquid Crystal OLEDs.

The electrical responses of a columnar liquid crystal (a diimidodiester derivative of benzo[ghi]perylene) deposited either by spin-coating or by thermal evaporation into a typical OLED device are compared. For the spin-coated film, homeotropic alignment was induced by thermal annealing, which enhanced the charge carrier mobility significantly. For the evaporated films, homeotropic alignment could not be obtained by annealing. However, a degree of rectification higher than 3 orders of magnitude was achieved, even without annealing, with an electrical response similar to the response of the aligned spin-coated film. A trap-limited space-charge-limited current model was used to extract the charge carrier mobility directly from the current-voltage curves. Grazing incidence wide-angle X-ray scattering confirmed the homeotropic alignment of the annealed spin-coated film, whereas the columns are mostly oriented parallel to the surface in the evaporated case. In a field-effect transistor with bottom-gate bottom-contact geometry, the evaporated film exhibited a typical behavior of an n-type transistor. The degree of intermolecular order is thereby strongly dependent on the deposition method where vacuum deposition leads to a higher order. This higher order, however, impedes reorientation by annealing of the evaporated film but leads to improved charge transport between the electrodes even without homeotropic alignment of columnar liquid crystal.

Nanostructured layer-by-layer films containing phaeophytin-b: electrochemical characterization for sensing purposes.

This paper reports the study and characterization of a new platform for practical applications, where the use of phaeophytin-b (phaeo-b), a compound derived from chlorophyll, was characterized and investigated for sensing purposes. Modified electrodes with nanostructured phaeo-b films were fabricated via the layer-by-layer (LbL) technique, where phaeo-b was assembled with cashew gum, a polysaccharide, or with poly(allylamine) hydrochloride (PAH). The multilayer formation was investigated with UV-Vis spectroscopy by monitoring the absorption band associated to phaeo-b at approximately 410 nm, where distinct molecular interactions between the materials were verified. The morphology of the films was analyzed by atomic force microscopy (AFM). The electrochemical properties through redox behavior of phaeo-b were studied with cyclic voltammetry. The produced films were applied as sensors for hydrogen peroxide (H2O2) detection. In terms of sensing, the cashew/phaeo-b film exhibited the most promising result, with a fast response and broad linear range upon the addition of H2O2. This approach provides a simple and inexpensive method for development of a nonenzymatic electrochemical sensor for H2O2.

Emission ellipsometry used to probe aggregation of the luminescent 2,1,3-benzothiadiazole dyes and ordering in an E7 liquid crystal matrix.

The incorporation of dyes in liquid crystal matrices has been exploited to produce enhanced displays, but it can also be used to probe ordering in liquid crystals and to assess intermolecular interactions and dye aggregation. In this study, we investigated polarized absorption and emission of the luminescent dyes 4,7-bis(2-(4-(decyloxy)phenyl)ethynyl)-[2,1,3]-benzothiadiazole (1A) and 4,7-bis{2-[4-(4-decylpiperazin-1-yl)phenyl]ethynyl}-[2,1,3]-benzothiadiazole (5A) in the E7® liquid crystal. The electronic structures of both 1A and 5A dyes were affected by the matrix and by the analysis of the line shape of emission we could determine that the dyes form J aggregates. This achievement is significant because obtaining this type of information for small molecules requires ordered matrices, which is difficult to obtain for these dyes. Using emission ellipsometry we were able to determine the ordering of the E7 molecules, but this was possible only with the larger 5A dye. The smaller 1A was not entirely ordered in the E7 matrix and this calls for caution in other types of work where dopants are used as probes to infer the properties of the matrix. The emission ellipsometry data for the dyes allowed us to detect the enhanced birefringence in the matrix, thus confirming the theoretical prediction.

Development and characterization of multilayer films of polyaniline, titanium dioxide and CTAB for potential antimicrobial applications.

Composites prepared from polyaniline (PANI) and the ceramic technology of titanium dioxide (TiO2) have been proposed, however, the interaction of these materials with greater control of molecular arrangement becomes attractive in order to achieve properties not previously described or yet the optimization of those already reported. Therefore, in this study, thin hybrid films made of polyaniline (PANI), a conductive polymer, and the technological ceramic, titanium dioxide (TiO2), were prepared by the layer-by-layer (LbL) self-assembly technique. The films were characterized by cyclic voltammetry (CV), UV-VIS spectroscopy and atomic force microscopy (AFM). Aiming to improve the dispersion of the ceramic in the polymer matrix, the commercial surfactant, cetyl trimethylammonium bromide (CTAB), was used in the formation of the films. The best condition of deposition was found showing synergic interactions between the conjugated materials. The antibacterial activity of the PANI(TiO2)/CTAB films was studied and the obtained results suggest their use as antimicrobial coatings.