Synthesis and Properties of Molecular Rods. 2. Zig-Zag Rods

Advances in the Chemistry of 2,4,6-Tri(thiophen-2-yl)-1,3,5-triazine

Heterocyclic systems are now considered to be an integral part of material chemistry. Thiophene, selenophene, furan, pyrrole, carbazole, triazine and others are some such examples worth mentioning. 2,4,6-Tri(thiophen-2-yl)-1,3,5-triazine is a C3h -symmetric system with thiophene as the donor unit and s-triazine as the acceptor unit. This review gives an insight into the advances made in the thienyl-triazine chemistry over the past two to three decades. The synthetic pathways for arriving at this system and all its important derivatives are provided. The major focus is on the materials synthesized using the thienyl-triazine system, including star molecules, linear and hyperbranched polymers, porous materials and their diverse applications. This review will play a catalytic role for new dimensions to be explored in thienyl-triazine chemistry.

Design of Collective Motions from Synthetic Molecular Switches, Rotors, and Motors

Precise control over molecular movement is of fundamental and practical importance in physics, biology, and chemistry. At nanoscale, the peculiar functioning principles and the synthesis of individual molecular actuators and machines has been the subject of intense investigations and debates over the past 60 years. In this review, we focus on the design of collective motions that are achieved by integrating, in space and time, several or many of these individual mechanical units together. In particular, we provide an in-depth look at the intermolecular couplings used to physically connect a number of artificial mechanically active molecular units such as photochromic molecular switches, nanomachines based on mechanical bonds, molecular rotors, and light-powered rotary motors. We highlight the various functioning principles that can lead to their collective motion at various length scales. We also emphasize how their synchronized, or desynchronized, mechanical behavior can lead to emerging functional properties and to their implementation into new active devices and materials.

Spectral Properties of Fluorogenic Thiophene-derived Triarylmethane Dyes

Spectral properties and fluorogenic behaviors of five novel thiophene variants of malachite green (MG), termed MGTs, were determined. Appreciable changes as a function of homologation and substitution pattern, including absorption band positions and intensities and fluorescence quantum yields were observed. In particular, the shorter wavelength y-band absorption was found to shift over a nearly 200 nm range based on aryl group variation, allowing fine-tuning of the excitation wavelength for these dyes. In addition, the fluorescence intensity of some MGTs increased significantly (up to 4600-fold) when the dye was bound to a cognate protein partner, which is potentially useful for cell imaging studies.

Multistep Oxidation of Diethynyl Oligophenylamine-Bridged Diruthenium and Diiron Complexes

Homo-dinuclear nonlinear complexes [{M(dppe)Cp*}₂{μ-(-C≡C)₂X}] (dppe = 1,2-bis(diphenylphosphino)ethane; Cp* = η⁵-C₅Me₅; X = triphenylamine (TPA), M = Ru (1a) and Fe (1b); X = N,N,N',N'-tetraphenylphenylene-1,4-diamine (TPPD), M = Ru (2a)) were prepared and characterized by ¹H, ¹³C, and ³¹P NMR spectroscopy and single-crystal X-ray diffraction (1a, 2a). Attempts to prepare the diiron analogue of 2a were not successful. Experimental data obtained from cyclic voltammetry, square wave voltammetry, UV-vis-NIR (NIR = near-infrared) spectro-electrochemistry, and very informative IR spectro-electrochemistry in the C≡C stretching region, combined with density functional theory calculations, afford to make an emphasizing assessment of the close association between the metal-ethynyl termini and the oligophenylamine bridge core as well as their respective involvement in sequential one-electron oxidations of these complexes. The anodic behavior of the homo-bimetallic complexes depends strongly both on the metal center and the length of the oligophenylamine bridge core. The poorly separated first two oxidations of diiron complex 1b are localized on the electronically nearly independent Fe termini. In contrast, diruthenium complex 1a exhibits a significantly delocalized character and a marked electronic communication between the ruthenium centers through the diethynyl-TPA bridge. The ruthenium-ethynyl halves in 2a, separated by the doubly extended and more flexible TPPD bridge core, show a lower degree of electronic coupling, resulting in close-lying first two anodic waves and the NIR electronic absorption of [2a]⁺ with an indistinctive intervalence charge transfer character. Finally, the third anodic waves in the voltammetric responses of the homo-bimetallic complexes are associated with the concurrent exclusive oxidation of the TPA or TPPD bridge cores.

Thiol–ene polymerization of oligospiroketal rods

The nucleophilic thiol–ene (thia-Michael) reaction between molecular rods bearing terminal thiols and bis-maleimides was investigated.

Rigid Rod-Based FRET Probes for Membrane Sensing Applications

Oligospirothioketal (OSTK) rods are presented as an adjustable scaffold for optical membrane probes. The OSTK rods are readily incorporated into lipid bilayers due to their hydrophobic backbones. Because of their high length-over-diameter aspect ratio, only a minimal disturbance of the lipid bilayer is caused. OSTK rods show outstanding rigidity and allow defined labeling with fluorescent dyes, yielding full control of the orientation between the dye and OSTK skeleton. This allows the construction of novel Förster resonance energy transfer probes with highly defined relative orientations of the transition dipole moments of the donor and acceptor dyes and makes the class of OSTK probes a powerful, flexible toolbox for optical biosensing applications. Data on steady-state and time-resolved fluorescence experiments investigating the incorporation of coumarin- and [1,3]dioxolo[4,5-f][1,3]benzo-dioxole-labeled OSTKs in large unilamellar vesicles are presented as a show case.

Controlling charge separation and recombination by chemical design in donor–acceptor dyads

Conjugated donor–acceptor block co-oligomers that self-organize into D–A mesomorphic arrays have raised increasing interest due to their potential applications in organic solar cells.

Dendrimers with Oligospiroketal (OSK) Building Blocks: Synthesis and Properties

The development of novel dendrimers containing oligospiroketal (OSK) rods as building blocks is described. The linkage between the core unit (CU), branching units (BU), and OSK rods relies on the CuAAC reaction between terminal alkynes and azides. Two different strategies of dendrimer synthesis were investigated and it was found that the convergent approach is clearly superior to the divergent one. SAXS measurements and MD simulations indicate that the obtained dendrimer features a globular structure with very low density. Obviously, the OSK rods stabilize a rather loose mass-fractal structure.

Articulated rods - a novel class of molecular rods based on oligospiroketals (OSK)

We developed a new type of molecular rods consisting of two (or more) rigid units linked by a flexible joint. Consequently we called these constructs articulated rods (ARs). The syntheses of ARs were carried out by a flexible and modular approach providing access to a number of compounds with various functionalizations in terminal positions. First applications were presented with pyrene, cinnamoyl and anthracenyl labelled ARs.

A high triplet-energy polymer: synthesis and photo-physical properties of a π-stacked vinyl polymer having a xanthone moiety in the side chain

Poly(xanthon-3-yl methacrylate) having a π-stacked conformation efficiently harvests photo excitation energy for sky blue phosphorescent emission of iridium bis[(4,6-difluorophenyl)pyridinato-N,C²]picolinate (FIrpic) in solution and in film.

Synthesis of closo- and nido-biscarboranes with rigid unsaturated linkers as precursors to linear metallacarborane-based molecular rods

Several biscarborane-type derivatives of 8-iodo-1,2-dicarba-closo-dodecaborane (1), suitable as the precursors of linear metallacarborane-based molecular rods, were prepared. The synthesized closo-compounds contained two carborane moieties connected through a rigid linear unsaturated linker. The linkers were based on ethynylene and para-phenylene fragments and their combinations. The deboronation of all reported closo-compounds was selective and afforded nido-products with open pentagonal faces on opposite sides of the molecule, parallel to each other and perpendicular to the main molecular axis. All of the closo and nido products were characterized by a variety of physical methods (NMR, HRMS, IR). The structures of closo-carboranes 3, 6, 9, and 14 and nido-carboranes 15 and 17 were established by X-ray diffraction.

Synthesis of Oligo(spiroketal)s from Naturally Occurring myo-Inositol

Dehydrating polycondensation of tetraol-type monomers derived from naturally occurring myo-inositol with 1,4-cyclohexanedione formed a series of oligo(spiroketal)s. One of the spiroketals had reactive allyl pendants, which were useful for side-chain modifications via thiol-ene chemistry.

Novel porous materials based on oligospiroketals (OSK)

New materials with moderately high porosity are accessible by polyacetalization under very mild conditions.

Synthesis of 1,4-bis(phenylethynyl)benzenes and their application as blue phase liquid crystal composition

A number of 1,4-bis(phenylethynyl)benzene derivatives (BPEBs) and their analogues with different numbers of side-substitute fluorine atoms on benzene rings, and alkyl chains, ethoxyl groups, fluorine atoms and trifluoromethyl groups as the end groups have been synthesized. The effects of the different substituents on their properties such as thermal behavior of melting point and clearing point, the temperature of nematic phase, optical anisotropy and dielectric anisotropy have been well investigated, and it has been found that some BPEBs have a wide range of the nematic phase temperature with high optical anisotropy (Δn) and acceptable dielectric anisotropy (Δε), which have been applied as the crucial compositions to constitute a liquid crystal mixture having the properties of Δε=29.0 and Δn=0.283 at 25 °C. With the addition of the chiral dopant to the obtained liquid crystal mixture, blue phase liquid crystal with a blue phase temperature range of 8 °C has been achieved.

How to specify the structure of substituted blade-like zigzag diamondoids

Abstract The dualist of an [n]diamondoid consists of vertices situated in the centers of each of the n adamantane units, and of edges connecting vertices corresponding to units sharing a chair-shaped hexagon of carbon atoms. Since the polycyclic structure of diamondoids is rather complex, so is their nomenclature. For specifying chemical constitution or isomerism of all diamondoids the Balaban-Schleyer graph-theoretical approach based on dualists has been generally adopted. However, when one needs to indicate the location of C and H atoms or of a substituent in a diamondoid or the stereochemical relationships between substituents, only the IUPAC polycycle nomenclature (von Baeyer nomenclature) provides the unique solution. This is so since each IUPAC name is associated with a unique atom numbering scheme. Diamondoids are classified into catamantanes (which can be regular or irregular), perimantanes, and coronamantanes. Regular catamantanes have molecular formulas C4n+6H4n+12. Among regular catamantanes, the rigid blade-shaped zigzag catamantanes (so called because their dualists consist of a zigzag line with a code of alternating digits 1 and 2) exhibit a simple pattern in their von Baeyer nomenclature. Their carbon atoms form a main ring with 4n + 4 atoms, and the remaining atoms form two 1-carbon bridges. All zigzag [n]catamantanes with n > 2 have quaternary carbon atoms, and the first bridgehead in the main ring is such an atom. Their partitioned formula is Cn−2(CH)2n+4(CH2)n+4. As a function of their parity, IUPAC names based on the von Baeyer approach have been devised for all zigzag catamantanes, allowing the unique location for every C and H atom. The dualist of such a zigzag catamantane defines a plane bisecting the molecule, and the stereochemical features of hydrogens attached to secondary carbon atoms can be specified relatively to that plane. Graphical abstract

Hybrid molecular systems containing tetrathiafulvalene and iron-alkynyl electrophores: five-component functional molecules obtained from C-H bond activation

Treatment of [Cp*(dppe)Fe-C≡C-TTFMe3] (1) with Ag[PF6] (3 equiv) in DMF provides the binuclear complex [Cp*(dppe)Fe=C=C=TTFMe2 =CH-CH=TTFMe2 =C=C=Fe(dppe)Cp*][PF6]2 (2[PF6 ]2) isolated as a deep-blue powder in 69 % yield. EPR monitoring of the reaction and comparison of the experimental and calculated EPR spectra allowed the identification of the radical salt [Cp*(dppe)Fe=C=C=TTFMe2 =CH][PF6]2 ([1-CH][PF6]) an intermediate of the reaction, which results from the activation of the methyl group attached in vicinal position with respect to the alkynyl-iron on the TTF ligand by the triple oxidation of 1 leading to its deprotonation by the solvent. The dimerization of [1-CH][PF6] through carbon-carbon bond formation provides 2[PF6]2. The cyclic voltammetry (CV) experiments show that 2[PF6]2 is subject to two sequential well-reversible one-electron reductions yielding the complexes 2[PF6] and 2. The CV also shows that further oxidation of 2[PF6]2 generates 2[PF6]n (n=3-6) at the electrode. Treatment of 2[PF6]2 with KOtBu provides 2[PF6] and 2 as stable powders. The salts 2[PF6] and 2[PF6]2 were characterized by XRD. The electronic structures of 2(n+) (n=0-2) were computed. The new complexes were also characterized by NMR, IR, Mössbauer, EPR, UV/Vis and NIR spectroscopies. The data show that the three complexes 2[PF6]n are iron(II) derivatives in the ground state. In the solid state, the dication 2(2+) is diamagnetic and has a bis(allenylidene-iron) structure with one positive charge on each iron building block. In solution, as a result of the thermal motion of the metal-carbon backbone, the triplet excited state becomes thermally accessible and equilibrium takes place between singlet and triplet states. In 2[PF6], the charge and the spin are both symmetrically distributed on the carbon bridge and only moderately on the iron and TTFMe2 electroactive centers.

Partitioned-formula periodic tables for diamond hydrocarbons (diamondoids)

Isomeric diamond hydrocarbons (diamondoids or polymantanes) with the same number n of adamantane units share the same molecular formula C(Q)(CH)(T)(CH(2))(S) and can be divided into valence isomers (denoted as Q-T-S) by partitioning the number C = Q + T + S of their carbon atoms according to whether they are quaternary, tertiary, or secondary. Vertices of dualists are the centers of adamantane units, and dualist edges connect vertices of adjacent adamantane units (sharing a chair-shaped hexagon). Dualists of diamondoids are hydrogen-depleted skeletons of staggered alkane or cycloalkane rotamers. Diamondoids with acyclic dualists can be classified as catamantanes, those having dualists with chair-shaped six-membered rings as perimantanes, and those having dualists with higher-membered rings that are not perimeters of hexagon-aggregates as coronamantanes. Diamondoids with n adamantane units may be classified into regular catamantanes when the molecular formula is C(4n+6)H(4n+12), and irregular polymantanes (catamantanes or perimantanes) when the number of carbon atoms is lower than 4n + 6. The derivation is presented of formula-periodic tables of regular and irregular diamondoids that allow a better understanding of the shapes and properties of these hydrocarbons for which many applications are predicted.