Regioselective Synthesis of Pyrrole-Based Poly(arylenevinylene)s via Mn-Catalyzed Hydroarylation Polyaddition.

Mn-catalyzed hydroarylation polyaddition of 1-(2-pyrimidinyl)pyrrole (1a) with aromatic diynes is investigated. The use of commercially available MnBr(CO)5 as a precatalyst under the optimized reaction conditions resulted in a site- and regioselective hydroarylation polyaddition, affording the corresponding poly(arylenevinylene)s (PAVs) with excellent vinylene selectivity. The reaction protocol eliminates the production of stoichiometric amounts of byproducts from the monomers. The nonstoichiometric polyaddition of an excess amount of 1a with aromatic diynes is also demonstrated. The 2-pyrimidinyl substituent promoted the intramolecular transfer of the Mn catalyst walking through the 1a moiety.

Molecular Design of Naphthalene- and Carbazole-Based Monomers for Regiospecific Synthesis of Poly(arylenevinylene)s via Co-Catalyzed Hydroarylation Polyaddition.

This study focuses on the development of regiospecific hydroarylation polyaddition of naphthalene- and carbazole-based monomers with diynes under mild reaction conditions at room temperature. A 1-pyrazole substituent serves as an appropriate directing group for a Co-catalyst to efficiently activate the C-H bonds of generally inactive six-membered aromatic hydrocarbons. The 1-pyrazole groups in 2,6-di(1-pyrazolyl)naphthalene adopt planar conformations and act as directing groups, resulting in a smooth hydroarylation reaction. In contrast, the reaction with 1,5-di(1-pyrazolyl)naphthalene do not proceed. The polyaddition reaction of 2,6-di(1-pyrazolyl)naphthalene selectively proceeds at 3,7-positions under mild reaction conditions at 30 °C, and yields corresponding poly(arylenevinylene) (PAV) with high molecular weight. This molecular design is also applicable to the hydroarylation polyaddition of carbazole; the polyaddition reaction of 9-(2-ethylhexyl)-3,6-di(1-pyrazolyl)carbazole selectively occurred at 2,7-positions. The optical and electronic properties of the synthesized compounds are evaluated. The obtained PAVs serve as an emitting material in organic light-emitting diode (OLED). This study aims to develop a Co-catalyzed hydroarylation polyaddition via C-H activation of generally inactive polyaromatic hydrocarbons (PAHs) under mild conditions.

Nonstoichiometric Direct Arylation Polymerization of Octafluorobiphenyl with 2,7-Diiodofluorene for Regulating CH Terminals of π-Conjugated Polymer.

Nonstoichiometric direct arylation polycondensation of 2,2',3,3',5,5',6,6'-octafluorobiphenyl with excess of 2,7-diiodo-9,9-dioctyl-9H-fluorene is demonstrated. Pd/Ag dual-catalyst system under water/2-methyltetrahydrofuran biphasic conditions enables direct arylation under mild conditions and promotes the intramolecular transfer of a Pd catalyst walking through the fluorene moiety. The nonstoichiometric direct arylation polycondensation under the optimized reaction conditions produces the corresponding π-conjugated polymer with a high molecular weight and terminal octafluorobiphenyl units at both ends.

Facile Synthesis of Bis-pentafluoroarylated Anthracene Derivatives for N-type Organic-Field-Effect Transistor Applications.

Diphenylanthracene (DPA) and its derivatives are promising semiconducting materials for p-type organic-field-effect transistors (OFETs). In this study, to develop n-type semiconducting materials with an anthracene core, pentafluorobenzene was introduced into anthracene by C-H direct arylation, enabling the synthesis of various bis(pentafluorophenyl)anthracene (DPA-F) derivatives. The high reactivity of the pentafluorobenzene C-H bond allows direct arylation for synthesizing DPA-F derivatives in a single step. The introduction of strong electron-withdrawing pentafluorophenyl groups provides the anthracene derivatives with n-type semiconducting properties, in contrast to the p-type properties of the parent DPAs. Among the synthesized compounds, 2,6-bis(pentafluorophenyl)anthracene shows a high electron mobility of 0.12±0.02 cm2 /Vs and an on/off ratio>106 in OFETs. The high crystallinity results in the smooth electron transport. This study provides a facile synthetic method for n-type semiconducting materials and insights into the molecular design of the positional effects of aromatic substituents on anthracene.

One-Pot Synthesis of Triazatriphenylene Using the Povarov Reaction.

The Povarov reaction combines aromatic amines, aldehydes, and alkynes in a single step and is regarded as an annulative π-extension reaction of aromatic amines. In this study, the Povarov reaction was investigated as an efficient tool for the synthesis of aza-polycyclic aromatic hydrocarbons via multiple π-extensions. The double Povarov reaction of 1,4-diaminobenzene yielded the 4,7-phenanthroline derivative as the major product, regardless of the steric repulsion in the product. The site selectivity mainly depended on the HOMO distribution of the intermediate rather than the steric factor. Based on these insights, a 1,5,9-triazatriphenylene derivative was synthesized via a triple Povarov reaction. The structures of the synthesized compounds were unambiguously determined by single-crystal X-ray diffraction analysis. The triazatriphenylene derivative formed a smooth and stable thin film upon vacuum vapor deposition and served as a hole-blocking material in organic light-emitting diodes.

Step-Economical Synthesis of Conjugated Polymer Materials Composed of Three Components: Donor, Acceptor, and π Units.

Conjugated polymers have immense potential for their use as semiconducting materials in organic optoelectronic devices. The improvement of synthetic methods for conjugated polymers is important for the practical application of conjugated polymers. For mass production, synthetic methods must be developed by considering the concerns regarding cost and environment. Reduction in the number of synthetic steps is an efficient approach to address these concerns. The utilization of direct CH functionalization is a reasonable strategy in monomer and polymer syntheses, because the prefunctionalization steps for CC bond formation can be eliminated. This review summarizes the recent developments in the efficient syntheses of conjugated polymers as well as their monomers via direct arylation (CH/CX coupling) and cross-dehydrogenative coupling (CH/CH coupling) reactions.

Synthesis of Pyrrole-Based Poly(arylenevinylene)s via Co-Catalyzed Hydroarylation of Alkynes.

Polyaddition via the Co-catalyzed hydroarylation of 1-(2-pyrimidinyl)pyrrole with aromatic diynes affords poly(arylenevinylene)s under mild conditions. This reaction avoids production of stoichiometric amounts of by-products. Although structural analysis of the obtained polymers reveals the presence of 1,1-vinylidene unit, switching the counter anion of the Co catalyst and steric hindrance of the diyne monomers improves the regioselectivity of the polymers. When a catalyst with bulky counter anions is used for the reaction of less hindered diyne monomers, 1,2-vinylene linkages are formed dominantly over 1,1-vinylidene linkages (93:7). The effect of the regioselectivity of the polymer on the optical and semiconducting properties is also evaluated.

Synthesis of Polyfluoro Arylene-Based Poly(arylenevinylene)s via Pd-Catalyzed Dehydrogenative Direct Alkenylation.

In this study, π-conjugated poly(arylenevinylene)s are synthesized via the Pd-catalyzed dehydrogenative direct alkenylation of polyfluoroarenes with diethenyl aromatic monomer. The introduction of a fluoro group promotes the cross-coupling reaction, and the formation of the undesired homocoupling byproduct is minimized by optimizing the reaction conditions. The polycondensation reactions lead to the formation of poly(arylenevinylene)s with a well-defined trans-configuration. The obtained polymers are evaluated as emitting materials for organic light-emitting diodes.

Modulation of the Emission Mode of a Pt(II) Complex via Intermolecular Interactions.

Compounds with controllable color emissions are potentially useful as photoluminescent materials in imaging and sensing applications. Multimolecular emission can be used realizing variable-color emitters and has been demonstrated in the solid state. However, achieving multimolecular emission in solution is difficult to control. In this study, we used a combination of intermolecular interactions, namely hydrogen bonding and solvophobic effect, to modulate multimolecular emissions. A designed Pt complex demonstrated three emission colors: blue (monomer emission), yellow (emission form hydrogen-bonded dimer), and orange (aggregate emission). All of the emission modes exhibited high luminescence quantum yields, as a result of their uniform assemblies.

Synthesis of Organic Optoelectronic Materials Using Direct C-H Functionalization.

Small molecules and polymers with conjugated structures can be used as organic optoelectronic materials. These molecules have conventionally been synthesized by cross-coupling reactions; however, in recent years, direct functionalization of C-H bonds has been used to synthesize organic optoelectronic materials. Representative reactions include direct arylation reactions (C-H/C-X couplings, with X being halogen or pseudo-halogen) and cross-dehydrogenative coupling (C-H/C-H cross-coupling) reactions. Although these reactions are convenient for short-step synthesis, they require regioselectivity in the C-H bonds and suppression of undesired homo-coupling side reactions. This review introduces examples of the synthesis of organic optoelectronic materials using two types of direct C-H functionalization reactions. In addition, we summarize our recent activities in the development of direct C-H functionalization reactions using fluorobenzenes as substrates. This review covers the reaction mechanism and material properties of the resulting products.

Mechanistic study on the reductive elimination of (aryl)(fluoroaryl)palladium complexes: a key step in regiospecific dehydrogenative cross-coupling.

Cross-dehydrogenative coupling (CDC) reactions have attracted attention as short-step synthetic methods for C-C bond formation. Recently, we have developed CDC reactions between naphthalene and fluorobenzene. Rather than exhibiting general regioselectivity, this reaction proceeds selectively at the ß-position of naphthalene. In this study, investigation using model complexes as reaction intermediates revealed that the origin of the unique selectivity is the exclusive occurrence of reductive elimination at the ß-position. Detailed studies on the reductive elimination showed that the steric hindrance of the naphthyl group and the electron-withdrawing properties of fluorobenzene determine the position at which the reductive elimination reaction proceeds. These results show that the selectivity of the C-H functionalisation of polycyclic aromatic hydrocarbons (PAHs) is determined not by the C-H cleavage step, but by the subsequent reductive elimination step. The regioselective CDC reaction was adaptable to various PAHs but was less selective for pyrene with extended π-conjugation. In fluorobenzene substrates, the F atoms at the two ortho positions of the C-H moiety are necessary for high selectivity. The substrate ranges are in good agreement with the proposed mechanism, in which the reductive elimination step determines the regioselectivity.

Near-unity angular anisotropy of circularly polarized luminescence from microspheres of monodispersed chiral conjugated polymers.

A microsphere, assembled from a chiral π-conjugated polymer with narrow polydispersity, features a well-organized twisted-bipolar structure and exhibits highly biased circularly polarized luminescence (CPL). The CPL emitted toward the equatorial direction is 61-fold greater than that emitted along the zenith direction, which is the highest anisotropy among existing microscopic CPL emitters.

Spherical assemblies from π-conjugated alternating copolymers: toward optoelectronic colloidal crystals.

Self-assembly of conducting polymers, which are often used as photoabsorbing, charge-transporting, and photoemission layers of organic photovoltaic and light-emitting devices, were comprehensively studied by means of slow precipitation from polymer solutions upon addition of a vapor of nonsolvents. Polymers such as polyfluorene and polythiophene having a single monomer component hardly formed defined and discrete objects but only gave ill-defined aggregates. In contrast, alternating copolymers typically having both fluorene and thiophene components in their repeating unit self-assembled into well-shaped spheres with diameters ranging from several hundreds of nanometers to several micrometers. Such clear differences in terms of the assembling geometries derive from the rigidity and crystallinity of the polymers, where the copolymers possess large steric hindrance on their backbone that reduces planarity of the polymers and inhibits anisotropic crystal growth, leading to the formation of structurally isotropic spheres. Changing the assembling parameters can systematically control diameter and deviation of the spheres. Furthermore, photocarrier lifetimes of the spheres were markedly enhanced by more than 3 orders of magnitude in comparison with those of cast films from their solutions. This research gives a useful guide for preparation of colloidal crystals from π-conjugated polymers toward their optoelectronic applications.

Detailed optimization of polycondensation reaction via direct C-H arylation of ethylenedioxythiophene.

The polycondensation reaction of 3,4-ethylenedioxythiophene with 2,7-dibromo-9,9-dioctylfluorene via Pd-catalyzed direct arylation gives poly[(3,4-ethylenedioxythiophene-2,5-diyl)-(9,9-dioctylfluorene-2,7-diyl)]. The reaction conditions are optimized in terms of the Pd precatalysts, reaction time, and carboxylic acid additives. The combination of 1 mol% Pd(OAc)(2) and 1-adamantanecarboxylic acid as an additive is the optimized catalytic system, and it yields the corresponding polymer with a molecular weight of 39,400 in 89% yield. The polycondensation reaction, followed by an end-capping reaction, effectively provides a linear polymer without Br terminals.

Synthesis of π-conjugated polymer consisting of pyrrole and fluorene units by Ru-catalyzed site-selective direct arylation polycondensation.

Polycondensation of 1-(2-pyrimidinyl)pyrrole with 2,7-dibromo-9,9-dioctylfluorene via Ru-catalyzed direct arylation gives the corresponding conjugated polymer with a molecular weight of 19 800 in 86% yield. The introduction of directing group, 2-pyrimidinyl substituent, into the pyrrole monomer induces ortho-metalation and provides the site-selective direct arylation polycondensation at the α-position of pyrrole unit without the protection of ß-position. The removal of 2-pyrimidinyl substituent on the pyrrole unit proceeds efficiently and results in the enhancement of coplanarity along the main chain of the polymer.

Hydrogen-bonding linkage of thymidine derivatives with carboxylic acid and pyridyl groups in a crystalline state.

Thymidine derivatives with carboxylic acid and pyridyl groups were synthesized for constructing one-dimensional network structure based on hydrogen bonding in crystalline state. The solid sate structures and hydrogen bonding networks of the thymidine derivatives were characterized by single X-ray diffraction analysis. The thymidine derivatives formed a zwitterion structure with a pyridinium proton and a carboxylate moiety in a crystalline state due to transfer of a proton from the carboxylic acid to the pyridyl moiety. Strong hydrogen bonds between the pyridinium proton and the carboxylate moiety connected the thymidine units, resulting in a one-dimensional polymeric structure with a uniform direction reminiscent of the structure of single-strand polythymidine. The chemical structure of the pyridyl group affects the hydrogen-bonding networks. The well-designed hydrogen-bonding interaction served as connecting parts for polythymidine mimics even in the presence of other hydrogen-bonding motifs such as nucleobases.

Flexible and Red-Emissive Organic Single-Crystal Microresonator for Efficient Active Waveguides.

We fabricated a flexible and red-emissive microcrystal resonator for highly efficient optical waveguiding. The microfiber crystals of diketopyrrolopyrrole (DPP) used in this work possess a high photoluminescence (PL) quantum efficiency (ΦPL = 0.45) and exhibit a micromechanical deformation shape in the curved state. The crystals show optical fringes in their PL spectra, suggesting the existence of a naturally formed Fabry-Pérot crystal resonator owing to its flat crystal surface. The group refractive index (ng) and Rabi splitting energy (ℏΩ) indicating the coupling strength between excitons and resonator photons are large (ng = 3.7-6.0, â„Ω = 1.38 eV), suggesting the strong confinement of waveguiding photons. Spatially resolved PL measurements revealed that the PL in a crystal fiber is efficiently waveguided, even in a curved crystal with a very small curvature radius of 11 µm. Strong photon confinement inside a crystal resonator is a plausible origin of efficient optical waveguiding.

Molecular design of organic superbases, azacalix[3](2,6)pyridines: catalysts for 1,2- and 1,4-additions.

The molecular design, characteristics, and catalytic activity of macrocyclic amino compounds, azacalix[3](2,6)pyridine derivatives, were studied. The introduction of an electron-donating group on the pyridine moiety and bridging amino phenyl group enabled the enhancement of the basicity of azacalix[3](2,6)pyridine up to pK(BH(+)) = 29.5 in CD(3)CN. These derivatives were shown to be efficient catalysts for 1,4-addition reactions of nitroalkanes or primary alcohols to α,ß-unsaturated carbonyl compounds and 1,2-addition reactions of nitroalkanes to aromatic aldehydes.

Unique regioselectivity of the Pd-catalysed cross-dehydrogenative coupling reaction of simple polyaromatic hydrocarbons with polyfluoroarenes.

A Pd-catalysed cross-dehydrogenative coupling reaction introduced two polyfluoroarenes into simple polyaromatic hydrocarbons at sterically favourable positions. An investigation of the reaction mechanism revealed that the unique regioselectivity was determined by the reductive elimination step rather than the C-H bond cleavage step.

Fluorescence Switchable Conjugated Polymer Microdisk Arrays by Cosolvent Vapor Annealing.

Depositing minute light emitters into a regular array is a basic but essential technique in display technology. However, conventional lithographic methodologies involve multistep and energy-consuming processes. Here, we develop a facile method in which organic and polymeric fluorescent dyes spontaneously aggregate to form a patterned microarray. We find that a thin film of fluorescent π-conjugated polymer transforms into micrometer-sized aggregates when exposed to binary organic vapor at ambient temperature. The arrayed microaggregates can be formed over the whole substrate surface when using a quartz substrate that is prepatterned with regular hydrophilic boxes and hydrophobic grids. The resultant microarray is applicable to optical memories and displays when photoswitchable fluorophores are doped into the polymer matrix.