Lipophilic biphenylthiophene‐ and phenanthrothiophene‐triazine compounds, BPTTn and CPTTn, respectively, were prepared by a tandem procedure involving successive Suzuki‐Miyaura coupling and Scholl ...cyclodehydrogenation reactions. These compounds display photoluminescence in solution and in thin film state, solvatochromism with increasing solvent's polarity, as well as acidochromism and metal ion recognition stimuli‐responsive fluorescence. Protonation of BPTT10 and CPTT10 by trifluoroacetic acid results in fluorescence quenching, which is reversibly restored once treated with triethylamine (ON‐OFF switch). DFT computational studies show that intramolecular charge transfer (ICT) phenomena occurs for both molecules, and reveal that protonation enhances the electron‐withdrawing ability of the triazine core and reduces the band gap. This acidochromic behavior was applied to a prototype fluorescent anti‐counterfeiting device. They also specifically recognize Fe3+ through coordination, and the recognition mechanism is closely related to the photoinduced electron transfer between Fe3+ and BPTT10/CPTT10. CPTTn self‐assemble into columnar rectangular (Colrec) mesophase, which can be modulated by oleic acid via the formation of a hydrogen‐bonded supramolecular liquid crystal hexagonal Colhex mesophase. Finally, CPTTn also form organic gels in alkanes at low critical gel concentration (3.0 mg/mL). Therefore, these star‐shaped triazine molecules possess many interesting features and thus hold great promises for information processing, liquid crystal semiconductors and organogelators.
Triazine‐based mesogens with three pending discoid arms have been shown to self‐organize into rectangular columnar mesophases and form gels in various solvents. The solvatochromic‐, acidochromic‐ and metal recognition‐response photoluminescence of these mesogens offer applications in stimuli‐responsive fluorescence anti‐counterfeiting and as selective metal‐ion recognition.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The straightforward synthesis of several Fluorinated Polycyclic Aromatic Hydrocarbons by the efficient, transition‐metal‐free, arene fluorine nucleophilic substitution reaction is described, and the ...full investigation of their liquid crystalline and optical properties reported. The key precursors for this study, i. e. 2,2’‐dilithio‐4,4′,5,5′‐tetraalkoxy‐1,1’‐biphenyl derivatives, were obtained in two steps from the highly selective Scholl oxidative homo‐coupling of 3,4‐dialkoxy‐1‐bromobenzene, followed by quantitative double‐lithiation. In situ room temperature nucleophilic annulation with either perfluorobenzene or perfluoronaphthalene leads to 1,2,3,4‐tetrafluoro‐6,7,10,11‐tetraalkxoytriphenylenes and 9,10,11,12,13,14‐hexafluoro‐2,3,6,7‐tetraalkoxybenzoftetraphenes, respectively, in good yields. Exploiting the same strategy, subsequent double annulations resulted in the formation of 9,18‐difluoro‐2,3,6,7,11,12,15,16‐octa(alkoxy)tribenzof,k,mtetraphenes and 9,10,19,20‐tetrafluoro‐2,3,6,7,12,13,16,17‐octakis(hexyloxy)tetrabenzoa,c,j,ltetracenes, respectively. Despite the presence of only four alkoxy chains, the polar “Janus” mesogens display a columnar hexagonal mesophase over broad temperature ranges, with higher mesophase stability than the archetypical 2,3,6,7,10,11‐hexa(alkoxy)triphenylenes and their hydrogenated counterparts. The improvement or induction of mesomorphism is attributed to efficient antiparallel face‐to‐face π‐stacking driven by the establishment of non‐covalent perfluoroarene‐arene intermolecular interactions. The larger lipophilic discotic π‐extended compounds also exhibit columnar mesomorphism, over similar temperature ranges and stability than their hydrogenated homologs. Finally, these fluorinated molecules form stringy gels in various solvents, and show interesting solvatochromic emission properties in solution as well as strong emission in thin films and gels.
The efficient synthesis of fluorous polyaromatic hydrocarbons via the arene‐fluorine nucleophilic substitution reaction offers a fast and clean synthetic route to highly π‐conjugated systems of interest for organic electronics. The development of long‐range noncovalent arene‐fluoroarene interactions enables the formation of broader and thermally more stable mesophases than their hydrogenated counterparts, as well as supramolecular luminescent gels and films.
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π-Extended pyrene compounds possess remarkable luminescent and semiconducting properties and are being intensively investigated as electroluminescent materials for potential uses in organic ...light-emitting diodes, transistors, and solar cells. Here, the synthesis of two sets of pyrene-containing π-conjugated polyaromatic regioisomers, namely 2,3,10,11,14,15,20,21-octaalkyloxypentabenzo
,
,
,
,
pentaphene (
) and 2,3,6,7,13,14,17,18-octaalkyloxydibenzo
,
phenanthro 9,10-
picene (
), is reported. They were obtained using the Suzuki-Miyaura cross-coupling in tandem with Scholl oxidative cyclodehydrogenation reactions from the easily accessible precursors 1,8- and 1,6-dibromopyrene, respectively. Both sets of compounds, equipped with eight peripheral aliphatic chains, self-assemble into a single hexagonal columnar mesophase, with one short-chain
homolog also exhibiting another columnar mesophase at a lower temperature, with a rectangular symmetry;
isomers also possess wider mesophase ranges and higher mesophases' stability than their
homologs. These polycyclic aromatic hydrocarbons all show a strong tendency of face-on orientation on the substrate and could be controlled to edge-on alignment through mechanical shearing of interest for their implementation in photoelectronic devices. In addition, both series
and
display green-yellow luminescence, with high fluorescence quantum yields, around 30%. In particular,
exhibit a blue shift phenomenon in both absorption and emission with respect to their
isomers. DFT results were in good agreement with the optical properties and with the stability ranges of the mesophases by confirming the higher divergence from the flatness of
compared with
. Based on these interesting properties, these isomers could be potentially applied not only in the field of fluorescent dyes but also in the field of organic photoelectric semiconductor materials as electron transport materials.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Four new donor–acceptor triads (D–A–D) based on discotic and arylene mesogens have been synthesized by using Sonogashira coupling and cyclization reactions. This family of triads consists of two ...side‐on pending triphenylene mesogens, acting as the electron‐donating groups (D), laterally connected through short lipophilic spacers to a central perylenediimide (PI), benzoghiperylenediimide (BI), or coronenediimide (CI) molecular unit, respectively, playing the role of the electron acceptor (A). All D–A–D triads self‐organize to form a lamello‐columnar oblique mesophase, with a highly segregated donor–acceptor (D–A) heterojunction organization, consequent to efficient molecular self‐sorting. The structure consists in the regular alternation of two disrupted rows of triphenylene columns and a continuous row of diimine species. High‐resolution STM images demonstrate that PI‐TP2 forms stable 2D self‐assembly nanostructures with some various degrees of regularity, whereas the other triads do not self‐organize into ordered architectures. The electron‐transport mobility of CI‐TP2, measured by time‐of‐flight at 200 °C in the mesophase, is one order of magnitude higher than the hole mobility. By means of this specific molecular designing idea, we realized and demonstrated for the first time the so‐called p–n heterojunction at the molecular level in which the electron‐rich triphenylene columns act as the hole transient pathways, and the coronenediimide stacks form the electron‐transport channels.
D–A discotic‐based triads: A new family of donor–acceptor (D–A) discotic‐based triads, forming mesomorphic semiconductors with long‐range ordered supramolecular architectures and high electronic charge mobility, have been designed and synthesized for their potential use in optoelectronic devices (see figure).
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Alzheimer's disease is one of the neurodegenerative disorders caused by neuronal degeneration and apoptosis in brain. Bacoside A and B isolated from the Bacopa monniera plant are responsible for ...cognitive effects. These compounds repair damaged neurons by promoting activity of kinases, synaptic activity restoration, and improvement of nerve transmission. The present study explored the effect of bacoside‐A3 on β‐amyloid‐induced reduction of U87MG cell viability, generation of oxidative radicals, and activation of nuclear factor‐κB. The U87MG cells were stimulated with β‐amyloid (10 μM) after 24 h of bacoside‐A3 pretreatment or without pretreatment to induce characteristics of Alzheimer disease in vitro. Sulforhodamine B (SRB) assay was used to count viable cells and ELISA kit for analysis of PGE2 secretion. The pretreatment with bacoside‐A3 prevented β‐amyloid‐mediated suppression of U87MG cell proliferation. Pretreatment of U87MG cells with bacoside‐A3 prior to β‐amyloid stimulation suppressed generation of ROS in a concentration‐based manner. The β‐amyloid‐mediated formation of iNOS in U87MG cells was suppressed by bacoside‐A3 in a dose‐based manner. The β‐amyloid‐mediated PGE2 secretion was suppressed by bacoside‐A3 pretreatment in U87MG cells in the dose‐based manner. The overexpression of COX‐2 by β‐amyloid stimulation was suppressed in bacoside‐A pretreated cells in the dose‐based manner. The bacoside‐A3 pretreatment prevented nuclear translocation of NF‐κB in U87MG cells in the dose‐based manner. In summary, bacoside‐A3 prevented β‐amyloid‐mediated suppression of U87MG cell viability, inhibited generation of oxidative radicals, PGE2, and synthesis of iNOS. Therefore, bacoside‐A3 has therapeutic potential for Alzheimer disease and further in vivo studies need to be performed.
Effect of bacoside‐A3 on COX‐2 level.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The synthesis of an exclusive family of liquid-crystalline dimers consisting of two protomesogenic triphenylene moieties connected
via
a rigid, π-conjugated bridge, and the study of their ...mesomorphous, gel self-assembly and optical properties as a function of the nature of the bridge are reported. Various triphenylene bridged dimers were successfully prepared by either palladium-catalyzed Suzuki-Miyaura cross-coupling between pentakis(alkoxy)triphenylene nonaflates and various commercially accessible aryldiboronic acids (as bridges) or by FeCl
3
-promoted Scholl oxidative homo-coupling of thiophene/thienothiophene/furan-containing pentakis(alkoxy)triphenylene derivatives. All linear dimers are mesomorphous, and self-organize into large multi-columnar rectangular superlattices, with columnar pairs arranged according to a chevron-like pattern, as deduced from SWAXS and supported by STM. At high temperature, most compounds also display a nematic columnar mesophase (N
Col
), easily recognized by characteristic optical textures. The transition temperature and mesophase ranges show a high dependency on the bridge nature and, to a lesser extent, on the chain-lengths around the triphenylene moieties. The sole kinked bridged-dimeric homolog of this series exhibits a single, room-temperature hexagonal mesophase (Col
hex
), as do the monofunctionalized triphenylene precursors, whereas the dimeric triphenylene with no bridge is not mesomorphous. UV-visible absorption and fluorescence emission spectra were measured in both solvents and thin films. The π-conjugated bridged-dimers exhibit emission spanning from 400-700 nm, thus covering the full visible-light range, whose emission maxima are obviously influenced by the chemical nature of the bridge. Furthermore, fluorescence quantum yields as high as 64% were measured for some of them. DFT theoretical computing calculations fully support the experimental measurements. Most dimers also form gels in cyclohexane and emit blue-to-orange light when irradiated by UV light; the corresponding xerogels revealed that their gelation ability results from the 3D morphology of entangled ultra-long and thin microfibers. The facile synthesis of these unique, multifunctional rigid discotic dimers, their rich mesomorphism, strong gelation ability and fine-tuned photophysical properties make these materials very attractive for the active field of organic electronics.
π-Conjugated liquid-crystalline dimers consisting of two triphenylene mesogens connected through a rigid molecular bridge have been synthesized. Mesophases, gels and optical properties have been investigated as a function of the bridge nature.
We report a straightforward and generic synthesis of several new series of annulated π‐extended poly‐(hetero)aromatic hydrocarbons (PAH), with carbazole, fluorene and fluorenone central building ...blocks by the Suzuki‐Miyaura/Scholl tandem reactions. The corresponding series of ditriphenylene discogens with a carbazole or a fluorenone central core, respectively, possess hexagonal columnar mesophases with broad mesophase ranges and high clearing points, as well as demonstrate a strong aggregation tendency in organic solvents as supergelators. The laterally‐substituted ditriphenylene mesogens based on dimethyl‐fluorene core exhibit a rich polymorphism with rectangular and hexagonal columnar mesophases from low temperatures onward, whereas their dioctyl‐fluorene homologues melt directly into the isotropic liquid without showing mesophases. These latter family of compounds are luminescent with very high fluorescent quantum yields, of around 70 % in solution, and show outstanding photocurrent behavior with charge carrier mobility in the 10−2 cm2 V−1 s−1 range, as measured by photocurrent transient time‐of‐flight (TOF) technique. This straightforward molecular design and simple synthetic strategy proved to be both potent and resilient, and could be generally applied to the fabrication of a great variety of other heteroarene molecular systems as organic semiconductors and electroluminescent materials for potentially low‐cost applications.
A generic synthetic method based on the Suzuki‐Scholl reactions was successfully exploited to yield new poly(hetero)aromatic hydrocarbons containing carbazole, fluorene or fluorenone moieties. These butterfly‐like mesogens exhibit columnar mesophases, form fibrous gels in various solvents, emit blue to orange light in films and solutions and show outstanding photocurrent behavior with charge carrier mobility in the ∼0.03 cm2 V−1 s−1 range.
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Controlling the chemo‐ and regioselectivity of transition‐metal‐catalyzed C−C activation remains a great challenge. The transformations of benzocyclobutenones (BCBs) usually involve the cleavage of ...C1−C2 bond. In this work, an unprecedented highly selective cleavage of C1−C8 bond with the insertion of alkynes is achieved by using blocking strategy via Ni catalysis, providing an efficient method for synthesis of 1,8‐disubstituted naphthalenes. Notably, the blocking group could be readily removed after the transformation.
A Ni‐catalyzed highly selective C1−C8 bond cleavage of BCBs with the insertion of alkynes was achieved by the assistance of a removable blocking group. This method provided an atom‐ and step‐economical approach to structurally important 1,8‐naphthalenediols under pH‐neutral conditions.
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Two series of regio-isomeric butterfly-shaped liquid crystalline systems, based on a ditriphenylenothiophene core (α/β-DTPT) equipped with eight peripheral long alkoxy chains, were synthesized in two ...steps by the Suzuki–Miyaura cross-coupling/Scholl cyclo-dehydrogenation reactions tandem from appropriate precursors. The influence of the core topology ( i.e. positional isomerism) on the mesomorphism, gelling self-assembly, absorption and luminescence, and charge-transport properties of both sets of isomers was investigated and compared. The six fused π-conjugated molecules systematically display columnar hexagonal (Col hex ) mesophases with β-fused ditriphenylenothiophene compounds (DTPTBn) showing more extended mesophase ranges and higher phase transition temperatures than their isomeric α-counterparts (DTPTAn). All ditriphenylenothiophenes also show strong aggregation behavior in organic solvents, and, in addition, good organic gelling abilities were found for the β-isomers. Interestingly too, high hole mobility rates greater than 10 −3 cm 2 V −1 s −1 were measured for the β-isomers, which were about 10 times higher than those of the α-counterparts. Modeling of the molecular structures combined with DFT calculations showed that the β-isomers possess flatter and more extended π-conjugated cores than the slightly distorted α-isomers, and consequently were more prone to optimize π–π intermolecular interactions, in agreement with the high-temperature mesophases and high charge carrier mobilities observed for these isomers. Finally, both sets of compounds emit blue-purple light in solution and the emission is substantially red-shifted when organized in films. DFT calculations of the HOMO–LUMO energy levels were also consistent with the optical measurements. This original molecular design and straightforward synthesis combination provides an efficient way to obtain novel π-extended organic, potentially semiconductor materials for further electronic device investigations.
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