Synthesis and characterization of a new class of liquid-crystalline, highly luminescent molecules containing a 2,4,6-triphenyl-1,3,5-triazine unit

Phenanthrothiophene-Triazine Star-Shaped Discotic Liquid Crystals: Synthesis, Self-Assembly, and Stimuli-Responsive Fluorescence Properties

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.

Aromatic Dendrimers Bearing 2,4,6-Triphenyl-1,3,5-triazine Cores and Their Photocatalytic Performance

The synthesis of two novel aromatic dendrimers structurally derived from 1,3,5-tri[1,3-diphenyl(phenyl-5-yl)phenyl-4′-yl]benzene and bearing 2,4,6-triphenyl-1,3,5-triazine cores is reported. The obtained dendrimers were used for the OLEDs construction, as well as in the role of innovative photocatalysts for the very efficient and selective oxidation of various benzylamines to respective N-benzylidene benzylamines under mild conditions.

Trithiazolyl-1,3,5-triazines bearing decyloxybenzene moieties: synthesis, photophysical and electrochemical properties, and self-assembly behavior

We synthesized the first members of trithiazolyl-1,3,5-triazines that combine attractive photophysical and self-assembling properties.

Contrasting effects of heterocycle substitution and branched tails in the arms of star-shaped molecules

Herein, heterocycle based star-shaped liquid crystalline tris(N-salicylideneaniline)s (TSANs) are reported.

Columnar propeller-like 1,3,5-triphenylbenzenes: the missing link of shape-persistent hekates

Triphenylbenzenes with different substitution patterns at the outer phenyl rings have been successfully synthesised. Sixfold n-alkoxy substitution was insufficient for mesomorphism, but already increasing the number of side chains by three methoxy groups led to liquid crystalline behaviour and mesophase formation. Symmetrical triphenylbenzenes with nine n-alkoxy side chains (≥C9) formed broad enantiotropic mesophases. The symmetry of the liquid crystalline phases was unambiguously determined by X-ray diffraction measurements as Colh and Colho for symmetry-reduced methoxy-alkoxy derivatives and symmetrical nona-alkoxy-triphenylbenzenes, respectively. Based on X-ray diffraction data a stacking model was proposed in which the single molecules aggregate to helical columns forming a mesophase.

3,6-Di(pyridin-2-yl)-1,2,4,5-tetrazine capped Pd(0) nanoparticles: a catalyst for copper-free Sonogashira coupling of aryl halides in aqueous medium

3,6-Di(pyridin-2-yl)-1,2,4,5-tetrazine (pytz) capped Pd(0) nanoparticles (TzPdNPs) act as a catalyst in Sonogashira coupling under copper- and ligand-free conditions in aqueous medium.

Electro-functional octupolar π-conjugated columnar liquid crystals

A series of propeller-shaped π-conjugated molecules based on 2,4,6-tris(thiophene-2-yl)-1,3,5-triazines has been designed and synthesized to obtain ambipolar charge-transporting liquid-crystalline materials. The 3-fold electron-donating aromatic units are attached to the electron-accepting triazine core, which forms electro-functional octupolar π-conjugated structures. These octupolar molecules self-organize into one-dimensional columnar nanostructures and exhibit ambipolar carrier transport behavior, which has been revealed by time-of-flight measurements. In this approach, electron-donor and acceptor electro-active segments are assembled individually in each column to give one-dimensional nanostructured materials with precisely tuned electronic properties. Their desirable electronic structures responsible for both hole and electron conductions have also been examined by cyclic voltammetry and theoretical calculations. The present results provide a new guideline and versatile approach to the design of ambipolar conductive nanostructured liquid-crystalline materials.

Star-Shaped Conjugated Systems

The present review deals with the preparation and the properties of star-shaped conjugated compounds. Three, four or six conjugated arms are attached to cross-conjugated cores, which consist of single atoms (B, C⁺, N), benzene or azine rings or polycyclic ring systems, as for example triphenylene or tristriazolotriazine. Many of these shape-persistent [n]star compounds tend to π-stacking and self-organization, and exhibit interesting properties in materials science: Linear and non-linear optics, electrical conductivity, electroluminescence, formation of liquid crystalline phases, etc.

A triazine-based three-directional rigid-rod tecton forms a novel 1D channel structure

A large, symmetrically substituted triazine-based molecule, synthesized by a copper-free Sonogashira coupling procedure self-assembles to form a novel 1D channel structure that hosts chlorobenzene molecules as guests.

Synthesis, Characterization, and Self-Assembly of Nitrogen-Containing Heterocoronenetetracarboxylic Acid Diimide Analogues: Photocyclization of N-Heterocycle-Substituted Perylene Bisimides

Novel dibenzocoronenetetracarboxylic acid diimide analogues and naphthoperylenetetracarboxylic acid diimide analogues containing imidazole, 1,2,4-triazole, and pyrazole rings embedded as functional constituents within the parent hydrocarbon backbone have been synthesized. The pi-rich and pi-poor heterocycles have different influences on the physical properties of the parent benzocoronenetetracarboxylic acid diimide and naphthoperylenetetracarboxylic acid diimide systems. The pi-rich 3 was able to self-assemble into one-dimensional nanostructures through strong pi-pi stacking, whereas the pi-poor 8 lacked the one-dimensional self-assembly capability, thus offering the potential to control the self-assembly capability of the pi-conjugated perylene core by decoration with N-heterocycles.

An Enantiomeric Nanoscale Architecture Obtained from a Pseudoenantiomeric Aggregate: Covalent Fixation of Helical Chirality Formed in Self-Assembled Discotic Triazine Triamides by Chiral Amplification

Covalent fixation of a chiral helical structure which is created in a self-assembling system by a chiral-amplification method based on the sergeants/soldiers principle is reported. Disk-shaped triazine triamides self-assembled to form columnar-type helical aggregates through pi-stacking interactions among the central triphenyltriazine moieties, hydrogen-bonding interactions among the amide groups, and van der Waals interactions among the alkyl groups in nonpolar solvents such as hexane, octane, toluene, and p-xylene. When the achiral triazine triamide soldier component is mixed with a tiny amount of the chiral triazine triamide sergeant component, control of the intrinsic supramolecular helicity of the self-assembled soldier component by the sergeant component leads to chiral amplification and formation of a pseudoenantiomeric aggregate with only one handedness of the helix. The helicity can be preserved by ring-closing olefin metathesis polymerization mediated by Grubbs catalyst when an achiral component with terminal olefinic groups forms the pseudoenantiomeric aggregate in the presence of a tiny amount of the chiral component without olefinic groups. After polymerization and removal of the chiral component, the polymeric architecture obtained from the achiral soldier component is optically active and thus can be regarded as an enantiomeric object in which the chiral information transferred from the chiral sergeant component is preserved. The nanoscale chiral structure is fixed perfectly, as indicated by CD spectroscopic evidence obtained in a polar THF medium at high temperature and low concentration. AFM and TEM observations show a nanoscale fibrous structure with a diameter of 2-4 nm, which corresponds to the molecular size of the triazine triamide monomer.

Highly Blue Luminescent Triazine−Amine Conjugated Oligomers

[Reaction: see text]. The novel synthetic strategy and optical properties of highly fluorescent, triazine-amine conjugated oligomers are described herein. Under basic conditions, aromatic dinitrile compounds, NC-C6H4-X-C6H4-CN (X = NMe, O, CH2), underwent cyclic trimerization of the cyano groups at both ends to give a series of triazine-containing oligomers. The oligomers can be expressed as (2n + 1) mer, where n represents the number of triazine rings in the oligomer. The absorption maximum of an amine-conjugated trimer (X = NMe, n = 1) was outstandingly red-shifted as compared with those of the other trimers (X = CH2, O). In acidic media, the amine-conjugated trimer showed two-step bathochromic shifts caused by protonation. The absorption maxima of the amine-conjugated (2n + 1) mers (X = NMe, n = 1-4) did not depend on n; instead, shoulder peaks appeared in the long-wavelength region when n 2. The oligomers involving alternate conjugation of triazines and NMe groups through phenylene groups showed strong fluorescence in chloroform. In particular, the pentamer was the most efficient blue emitter (PhiF = 0.82). The other triazine-containing oligomers (X = CH2, O) did not show fluorescence at all. Therefore, it is concluded that the emission properties are due to the strong electron-donating and accepting abilities of the NMe and triazine moieties, respectively.

Highly Fluorescent N,N-Dimethylaminophenylethynylarenes: Synthesis, Photophysical Properties, and Electrochemiluminescence

A new family of aryl-pi-donor-aryl molecules has been synthesized and studied with respect to their photophysical properties and electrogenerated chemiluminscence (ECL) for the first time. Anthracene, phenanthrene, naphthalene, biphenyl, and fluorene were coupled with N,N-dimethylanilino moiety via a C-C triple bond (1-7). Introduction of such a strong electron-donating moiety as N,N-dimethylanilino group through a triple bond imparts new properties to the resultant molecules that are not commonly observed for the parent arenes. All molecules show absorption in the near-visible region and emission totally in the visible region with high fluorescence quantum yields. Bright solid-state photoluminescence has also been noticed for all the compounds in the visible region. 9-Anthryl- and 1-naphthyl- derivatives exhibited blue-shifted electrochemiluminescence (ECL) relative to their photoluminescence because of aggregation. 9-Phenanthryl- and 2-naphthyl- derivatives did not show ECL. 2-Biphenyl derivative showed monomeric ECL while 4-biphenyl counterpart exhibited excimer ECL. No ECL was observed for 2-fluorenyl derivative. The observed electronic properties are discussed with regard to the structure of the molecules. The characteristics of the molecules chosen in the present study open up new prospects and promises for novel tunable organic materials, on the basis of simple extension of conjugation to promote intramolecular communication, for ECL, OLED, and other optoelectronic applications.

Gold Liquid Crystals Displaying Luminescence in the Mesophase and Short F⋅⋅⋅F Interactions in the Solid State

Rodlike gold(I) complexes, [Au(C6F4OCmH2m+1)(C(triple bond)NC6H4C6H4OCnH2n+1)] (m=2, n=4, 10; m=6, n=10; m=10, n=6, 10), display interesting features. They are liquid crystals and show photoluminescence in the mesophase, as well as in the solid state and in solution. The single-crystal, X-ray diffraction structure of [Au(C6F4OC2H5)(C(triple bond)NC6H4C6H4OC4H9)] confirms its rodlike structure, with a linear coordination around the gold atom, and reveals the absence of any Au...Au interactions (such interactions are often present in luminescent gold complexes). Well-defined, intermolecular Fortho...Fmeta interactions, with remarkably short intermolecular FF distances (2.66 A), are observed; these interactions seem to be responsible for the crystal packing, which consists of an antiparallel arrangement of molecules. Experiments under different conditions support the explanation that the photoluminescence has an intramolecular origin.