Elektrolumineszierende konjugierte Polymere – Polymere erstrahlen in neuem Licht

Ultrafast Halogen Dance Reactions of Bromoarenes Enabled by Catalytic Potassium Hexamethyldisilazide

Lochmann-Schlosser base, a stoichiometric combination of nBuLi and KOtBu, is commonly used as a superbase for deprotonating a wide range of organic compounds. In the present study, we report that catalytic potassium hexamethyldisilazide (KHMDS) exhibits higher catalytic activity than KOtBu for successive bromine-metal exchanges. Accordingly, 1-10 mol% of KHMDS dramatically enhances halogen dance reactions to introduce various electrophiles to bromopyridine, bromoimidazole, bromothiophene, bromofuran, and bromobenzene derivatives with the bromo group translocated from the original position. A dual catalytic cycle is proposed to explain the ultrafast bromine transfer.

Polarity and strong sensitivity to external electric field in azacrown oligophenylenevinylene

Complex study of quadrupolar azacrown dye (E,E)-5,5́-Bis[2-(4-(4',7',10',13',16'-pentaoxa-1 azacyclooctadecyl)phenyl)ethenyl]-2,2́-bipyridine 1 was performed. Electronic spectra of absorption and fluorescence in different solvents exhibit strong solvatochromism. Electrooptical absorption measurements (EOAM) were performed to determine the electric dipole moments. These measurements gave large values of dipole moments in the ground μ_g and Franck-Condon excited state μ_e^FC equal to 6.8 ± 0.14C m and 39.3 ± 0.3C m, respectively. Furthermore, the results of EOAM suggest the existence two conformers in the ground state with close energies of electronic transitions. Density functional theory (DFT) calculations directly show that the shape of this molecule is not planar in the ground state and also allows the existence of two stable conformers with close energies. They appeared due to different orientations of the left and right pyridine fragments of the solute. The energies, electric dipole moments and dependences of dipole moments on the strength of applied electric field were calculated for found stable conformers of 1. DFT calculations with TD / B3LYP / 3-21G and cc-pVDZ (Time Depend) approach show that external electric field increases dramatically the dipole moments of the solute under study. The higher field intensity the larger the excited electric dipole in the range intensities from zero to ∼ 2.8·× 10 ⁹ V/m.

Solvatochromy and symmetry breaking in two quadrupolar oligophenylenevinylenes

Electrooptical absorption measurements (EOAM), solvatochromic dependences and quantum chemical simulations testify to large dipole moments change of two quadrupolar oligophenylenevinylenes upon transition to Franck-Condon excited state μ_e^FC. The values of the dipole moments μ_g and μ_e^FC are in the range [(4.2 - 4.9)10³⁰] C m and (30.8 - 47.0)10³⁰C m, respectively. The relations of dipole moments in the ground and excited states determined by EOAM correlate well with results obtained via the solvatochromic method. Calculations carried out by density functional theory (DFT) show that optimized configuration of the ground state of these molecules is not planar. The results from all methods applied unequivocally show the structural symmetry breaking in the studied compounds.

Twining Poly(polyoxometalate) Chains into Nanoropes

Organic polymers and inorganic clusters belong to two different disciplines and have completely different properties and structures. When a cluster is attached to the backbone of a polymer as a pendant, the resultant hybrid polymers (polyclusters) exhibit unique behaviours totally different from those of conventional polymers owing to the nanoscale size of the cluster and its particular interactions. Herein, the aggregation of a poly(polyoxometalate)-a polynorbornene backbone with inorganic polyoxometalate cluster pendants-upon addition of a non-solvent to its dilute solution is reported. A three-dimensional network of tangled and snake-like nanothreads was observed. Direct visualisation of individual nanoscale clusters enabled identification of single chains within the nanothreads. These observations suggest that during the process of aggregation, the hybrid polymer forms curved or extended chains as a consequence of an armouring effect in which the collapsed cluster pendants wrap around the backbone. The collapse occurs because they become less soluble in the solvent/non-solvent mixture. The extended chains then become entwined and form nanoropes consisting of multiple chains wound around each other. This study provides a deeper understanding of the nature of polyclusters and should also prove useful for their future development and application.

Novel Conjugated Side Chain Fluorinated Polymers Based on Fluorene for Light-Emitting and Ternary Flash Memory Devices

Three novel conjugated polymers based on 9,9'-dioctylfluorene unit and isoindolo[2,1-a]benzimidazol-11-one with different fluorine substituents (0, 2 and 4) were synthesized. PLED and resistive memory devices based on these polymers were prepared consequently. PLED based on four-fluorinated polymer showed the highest maximum brightness of 3192 cd m-2 with almost 5-fold increase of current efficiency 8-fold increase of external quantum efficiency compared to that of the other two, and all the PLEDs exhibited good emission stability with no noticeable change of electroluminescence even under high voltage of 10 V. The memory device of doubly-fluorinated polymer exhibited ternary flash behavior with threshold voltages below -2.5 V, while device of four-fluorinated polymer possessed ON/OFF current ratio above 104. Impact of fluorine substitutions on the performance of devices were briefly investigated. The results revealed that the improvement of device performance might not scale with the increasing number of fluorine substitutions, and the four-fluorine-substituted polymer and doubly-fluorinated polymer could be encouraging materials for applications of PLED and resistive memory device and worth of further design of other new polymer systems.

Columnar Self-Assembly of Electron-Deficient Dendronized Bay-Annulated Perylene Bisimides

Three new heteroatom bay-annulated perylene bisimides (PBIs) have been synthesized by microwave-assisted synthesis in excellent yield. N-annulated and S-annulated perylene bisimides exhibited columnar hexagonal phase, whereas Se-annulated perylene bisimide exhibited low temperature columnar oblique phase in addition to the high temperature columnar hexagonal phase. The cup shaped bay-annulated PBIs pack into columns with enhanced intermolecular interactions. In comparison to PBI, these molecules exhibited lower melting and clearing temperature, with good solubility. A small red shift in the absorption was seen in the case of N-annulated PBI, whereas S- and Se-annulated PBIs exhibited blue-shifted absorption spectra. Bay-annulation increased the HOMO and LUMO levels of the N-annulated perylene bisimide, whereas a slight increase in the LUMO level and a decrease in the HOMO levels were observed in the case of S- and Se-annulated perylene bisimides, in comparison to the simple perylene bisimide. The band gaps of PBI and PBI-N were almost same, whereas an increase in the band gaps were observed in the case of S- and Se-annulated PBIs. The tendency to freeze in the ordered glassy columnar phase for PBI-N and PBI-S will help to overcome the charge traps due to crystallization, which are detrimental to one-dimensional charge carrier mobility. These solution processable electron deficient columnar semiconductors possessing good thermal stability may form an easily accessible promising class of n-type materials.

Controllable Activation of Pd-G3 Palladacycle Precatalyst in the Presence of Thiosugars: Rapid Access to 1-Aminobiphenyl Thioglycoside Atropoisomers at Room Temperature

A controllable method for the functionalization of XantPhos Pd-G3 precatalyst with thiosugars and thiols has been established. Under mild and operationally simple reaction conditions through just mixing of precatalyst and thiosugars (α- or β-mono-, di- and poly-thiosugar derivatives) in water at 25 °C for 20 min, a series of 1-aminobiphenyl thioglycosides that are difficult to synthesize by classical methods has been synthesized in very high yields.

NIR-Absorbing Donor-Acceptor Based 1,1,4,4-Tetracyanobuta-1,3-Diene (TCBD)- and Cyclohexa-2,5-Diene-1,4-Ylidene-Expanded TCBD-Substituted Ferrocenyl Phenothiazines

A series of unsymmetrical (D-A-D₁ , D₁ -π-D-A-D₁ , and D₁ -A₁ -D-A₂ -D₁ ; A=acceptor, D=donor) and symmetrical (D₁ -A-D-A-D₁ ) phenothiazines (4 b, 4 c, 4 c', 5 b, 5 c, 5 d, 5 d', 5 e, 5 e', 5 f, and 5 f') were designed and synthesized by a [2+2] cycloaddition-electrocyclic ring-opening reaction of ferrocenyl-substituted phenothiazines with tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). The photophysical, electrochemical, and computational studies show a strong charge-transfer (CT) interaction in the phenothiazine derivatives that can be tuned by varying the number of TCNE/TCNQ acceptors. Phenothiazines 4 b, 4 c, 4 c', 5 b, 5 c, 5 d, 5 d', 5 e, 5 e', 5 f and 5 f' show redshifted absorption in the λ=400 to 900 nm region, as a result of a low HOMO-LUMO gap, which is supported by TD-DFT calculations. The electrochemical study exhibits reduction waves at low potential due to strong 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) and cyclohexa-2,5-diene-1,4-ylidene-expanded TCBD acceptors. The incorporation of cyclohexa-2,5-diene-1,4-ylidene-expanded TCBD stabilized the LUMO energy level to a greater extent than TCBD.

PPV Polymerization through the Gilch Route: Diradical Character of Monomers

Despite various studies on the polymerization of poly(p-phenylene vinylene) (PPV) through different precursor routes, detailed mechanistic knowledge on the individual reaction steps and intermediates is still incomplete. The present study aims to gain more insight into the radical polymerization of PPV through the Gilch route. The initial steps of the polymerization involve the formation of a p-quinodimethane intermediate, which spontaneously self-initiates through a dimerization process leading to the formation of diradical species; chain propagation ensues on both sides of the diradical or chain termination occurs by the formation of side products, such as [2.2]paracyclophanes. Furthermore, different p-quinodimethane systems were assessed with respect to the size of their aromatic core as well as the presence of heteroatoms in/on the conjugated system. The nature of the aromatic core and the specific substituents alter the electronic structure of the p-quinodimethane monomers, affecting the mechanism of polymerization. The diradical character of the monomers has been investigated with several advanced methodologies, such as spin-projected UHF, CASSCF, CASPT2, and DMRG calculations. It was shown that larger aromatic cores led to a higher diradical character in the monomers, which in turn is proposed to cause rapid initiation.

Relayed Regioselective Alkynylation/Olefination of Unsymmetrical Cyclic Diaryliodonium Species Catalyzed by Cu and Pd: Affording Fluorescent Cytotoxic Benzoxazoles

Although cyclic diaryliodonium species have the potential to act as valuable synthons for cascade transformations, they still remain largely unexplored. The regioselectivity associated with unsymmetrical cyclic diaryliodonium species has previously been known to pose a challenge. A regioselective relayed alkynylation and olefination of unsymmetrical cyclic diaryliodonium species has been achieved by installation of a directing amido group. These relayed transformations were delayed until an oxazole ring had formed, delivering a series of unique fluorescent benzoxazoles. Moreover, some of these synthetic benzoxazoles showed apparent inhibitory activity against malignant cancer cells. Further confocal visualization revealed that benzoxazoles targeted cell nuclei. These findings might provide a novel structural scaffold to develop desirable anticancer agents.

X-ray structures of precursors of styrylpyridine-derivatives used to obtain 4-((E)-2-(pyridin-2-yl)vinyl)benzamido-TEMPO: synthesis and characterization

The synthesis and characterization of the precursor isomers trans-4-(2-(pyridin-2-yl)vinylbenzaldehyde (I), trans-4-(2-(pyridin-4-yl)vinylbenzaldehyde (II), trans-4-(2-(pyridin-2-yl)vinylbenzoic acid (III) and (E)-4-(2-(pydridin-4-yl)vinylbenzoic acid (IV) are reported. These compounds were prepared in order to obtain trans-4-((E)-2-(pyridin-2-yl)vinyl)benzamide-TEMPO (V). Compounds I and II were obtained by using a Knoevenagel reaction in the absence of a condensing agent and solvent. Oxidation of the aldehyde group using the Jones reagent afforded the corresponding acid forms III and IV. A condensation reaction with 4-amino-TEMPO using oxalyl chloride/DMF/CH2Cl2 provided the 4-((E)-2-(pyridin-2-yl)vinyl)benzamide-TEMPO. Single crystals of compounds I, II and III were obtained and characterized by X-ray diffraction. Compound I belongs to space group P2(1)/c, a = 12.6674(19) Å, b = 7.2173(11) Å, c = 11.5877(14) Å, b = 97.203(13)° and the asymmetric unit was Z = 4, whereas compound II was in the space group P2(1), with a = 3.85728(9) Å, b = 10.62375(19) Å, c = 12.8625(2) Å, b = 91.722 (2)° and the asymmetric unit was Z = 2. Compound III crystallized as single colorless needle crystals, belonging to the monoclinic system with space group P2(1), with Z = 2, with a = 3.89359(7) Å, b = 17.7014(3) Å, c = 8.04530(12) Å, b = 94.4030 (16)°. All compounds were completely characterized by IR, (1)H-NMR, EI-MS and UV-Vis.

Germacyclobutenes: generation by 1,1-carbalumination or 1,1-carbagallation and their photophysical properties

Aluminium- and gallium-functionalised alkenylalkynylgermanes, R(1) 2 Ge(C≡C-R(2) )[C{E(CMe3 )2 }=C(H)-R(2) ] (E=Al, Ga), exhibit a close contact between the coordinatively unsaturated Al or Ga atoms and the α-C atoms of the intact ethynyl groups. These interactions activate the Ge-C(alkynyl) bonds and favour the thermally induced insertion of these C atoms into the E-C(vinyl) bonds by means of 1,1-carbalumination or 1,1-carbagallation reactions. For the first time the latter method was shown to be a powerful alternative to known metallation processes. Germacyclobutenes with an unsaturated GeC3 heterocycle and endo- and exocyclic C=C bonds resulted from concomitant Ge-C bond formation to the β-C atoms of the alkynyl groups. These heterocyclic compounds show an interesting photoluminescence behaviour with Stokes shifts of >110 nm. The fascinating properties are based on extended π-delocalisation including σ*-orbitals localised at Ge and Al. High-level quantum chemical DFT and TD-DFT calculations for an Al compound were applied to elucidate their absorption and emission properties. They revealed a biradical excited state with the transfer of a π-electron into the empty p-orbital at Al and a pyramidalisation of the metal atom.

Carboxylic acids as traceless directing groups for the rhodium(III)-catalyzed decarboxylative C-H arylation of thiophenes

A rhodium(III)-catalyzed carboxylic acid directed decarboxylative C-H/C-H cross-coupling of carboxylic acids with thiophenes has been developed. With a slight adjustment of the reaction conditions based on the nature of the substrates, aryl carboxylic acids with a variety of substituents could serve as suitable coupling partners, and a broad variety of functional groups were tolerated. This method provides straightforward access to biaryl scaffolds with diverse substitution patterns, many of which have conventionally been synthesized through lengthy synthetic sequences. An illustrative example is the one-step gram-scale synthesis of a biologically active 3,5-substituted 2-arylthiophene by way of the current method.

Synthesis, Crystal Structures and Properties of 1,8-Di(Quinol-2-yl)Octa-1,7-Diyne and 1,8-di(Phenantren-9-yl)Octa-1,7-Diyne

1,8-Di(quinol-2-yl)octa-1,7-diyne and 1,8-di(phenanthren-9-yl)octa-1,7-diyne were synthesised by conventional and microwave-assisted methods in good yields. Microwave irradiation enhances the rate of these reactions. Photophysical properties of these derivatives were also evaluated, and it was found that 1,8-di(phenanthren-9-yl)octa-1,7-diyne displays a higher fluorescence quantum yield than 1,8-di(quinol-2-yl)octa-1,7-diyne. The molecular structures of 1,8-di(quinol-2-yl)octa-1,7-diyne and 1,8-di(phenanthren-9-yl)octa-1,7-diyne were established by single-crystal X-ray diffraction studies.